Prediction on detection and characterization of Galactic disk microlensing events by LSST
Upcoming LSST survey gives an unprecedented opportunity for studying populations of intrinsically faint objects using microlensing technique. Large field of view and aperture allow effective time-series observations of many stars in Galactic disk and bulge. Here, we combine Galactic models (for ) and simulations of LSST observations to study how different observing strategies affect the number and properties of microlensing events detected by LSST. We predict that LSST will mostly observe long duration microlensing events due to the source stars with the averaged magnitude around in band, rather than high-magnification events due to fainter source stars. In Galactic bulge fields, LSST should detect on the order of microlensing events per square degree as compared to in disk fields. Improving the cadence increases the number of detectable microlensing events, e.g., improving the cadence from to days approximately doubles the number of microlensing events throughout the Galaxy. According to the current LSST strategy, it will observe some fields times during a year survey with the average cadence of (I) and other fields (mostly toward the Galactic disk) around times during a year survey only with the average cadence (II). We anticipate that the number of events corresponding to these strategies are and , respectively. Toward similar lines of sight, LSST with the first observing strategy (I) will detect more and on average longer microlensing events than those observable with the second strategy. If LSST spends enough time observing near Galactic plane, then the large number of microlensing events will allow studying Galactic distribution of planets and finding isolated black holes among wealth of other science cases.
The Large Synoptic Survey Telescope (LSST) is an optical and wide-field telescope whose primary mirror has diameter and is now under construction in Chile (Ivezic et al., 2009). LSST is supposed to observe the most of the visible sky every days. Its field of view (FoV) and lifetime will be and years, respectively. The exposure time for each field will be . During a night, LSST will observe each field twice with visits separated by minutes (LSST Science Collaboration et al., 2017). Hence, LSST will take about images for most fields in the visible sky during its lifetime, i.e., the total number of visits in years is anticipated to be about million. Also percent of its time will be allocated to uniform observations with a constant cadence and during the rest of time, LSST will observe with other strategies.
LSST will (i) measure weak gravitational lensing to probe for any signals of dark energy and dark matter, (ii) map our galaxy and its objects, (iii) make an inventory of solar system components, and (iv) detect transient phenomena in optical band such as supernovae (Ivezic et al., 2009). However, other astrophysical events will be detected during the LSST lifetime. For instance, if Galactic disk is observed uniformly, then many microlensing events toward the Galactic bulge and disk will be detected. In this regard, Gould (2013) studied the possibility of probing the planet distribution in the Galactic plane by microlensing detection in addition to the transit technique.
When the light of a background source star passes through the gravitational field of a foreground massive object, it is bent toward the center of gravity, the so-called gravitational lensing event. In the Galactic scales, the light from a distant star can be lensed and as a result magnified by a collinear massive object which is called a gravitational microlensing event (Einstein, 1936). In these events the light from the background source star is magnified and produces two deformed images with unresolvable angular separation.
Detecting microlensing events toward the Galactic disk by a survey telescope helps constraining the mass, spatial and velocity stellar distributions in the Galactic thin and thick disks and the Galactic bar. Probing microlensing events during seasons toward directions in the Galactic plane was done by EROS-II (Rahal et al., 2009). As a result of this project, microlensing candidates have been found. By performing a Monte Carlo simulation according to the EROS-II observing strategy and comparing the results from simulation with the real observation, Moniez et al. (2017) could test the Galactic models, different mass functions, etc. The problems with microlensing events toward the Galactic plane are: (i) we do not know source distances, whereas toward the Galactic bulge almost all of the source stars belong to the Galactic bulge and are located at the distance of approximately far from us and (ii) the interstellar extinction is high and variable in both quantity and quality toward the Galactic disk. We lack detailed knowledge about extinction in the disk because there is no group of stars for which we apriority know colors and can be easily selected (red clump stars serve in the bulge). The poorly known extinction hampers optimizing observations and makes determination of event properties harder, (i.e., the source angular size, the size of the Einstein ring). These issues increase the number of degenerate physical parameters. However, the overall distributions of the observable parameters from observations can be used to examine the different models in the Galaxy.
LSST is suppose to uniformly observe the galactic plane. As a result, it will detect large number of microlensing events toward the Galactic disk and bulge and its results will help to probe different Galactic models of mass, velocity, special distribution, etc. In this work, we aim to simulate LSST observations toward the the Galactic bulge and disk with its observing strategies to predict detections of the Galactic disk microlensing events. We aim to specify the characteristics and statistics of the disk microlensing events which will be detected during its era. However, we do not consider the case of LSST providing supporting observations for the WFIRST microlensing survey to measure free-floating planet masses.
We perform a Monte Carlo simulation of detectable microlensing
events during the LSST lifetime according to its observing strategy
in details explained in section (2). In the following
section, we discuss the optical depth, the rate of events and the
number of observable events toward different directions resulted
from the simulation. Also we discuss the impact of observing cadence
on the results. In the section (4), we simulate observing
microlensing events by considering two strategies for observation
(I) epochs during years observation with the
cadence and (II) epochs during the first year
with the cadence, to predict statistics and
properties of detectable microlensing events with these strategies.
We summarize the results and conclude in the section
2. Modeling of LSST microlensing observations
In order to simulate the microlensing events detectable by LSST, we (i) simulate an ensemble of model microlensing events toward different directions in the Galactic plane, (ii) generate synthetic data points for each of them by assuming that these events are being observed by LSST, and finally (iii) exert some criteria as detectability threshold to simulated microlensing events to determine (a) the LSST ability of detecting bulge and disk microlensing events and (b) the characteristics of these events. These three steps are discussed in the following subsections, respectively.
2.1. Simulating disk microlensing events
In the following, we illustrate how to generate the parameters of the source and the lens stars to make microlensing model light curves. For the source stars, their locations are specified according to the overall mass density throughout the Galaxy versus distance in a given direction , where is total mass density due to all stellar structures in our galaxy, i.e., the thin and thick disks, Galactic bulge (and bar), and the stellar halo, is the source distance from the observer, and and represent the Galactic longitude and latitude respectively. We model these mass densities using the Besançon model (Robin et al., 2003, 2012). One can find all details of these mass density profiles in the Appendix B of Moniez et al. (2017). The map of total mass in the unit of per line of sight in the Galaxy is shown in Figure 1. In the simulation, the area corresponding to each line of sight is .
We indicate the intrinsic photometric properties of the source stars in the same way as Penny et al. (2017) and use the old public version of the Besançon model111 We used the version available at http://model.obs-besancon.fr/. There is a newer version from 2016: http://modele2016.obs-besancon.fr/. For each structure, we simulate a sample of stars in CFHTLS-Megacam photometry system222 http://www.cfht.hawaii.edu/Instruments/Imaging/Megacam/ without considering extinction. Then, the magnitudes in these filters, , are converted to the magnitudes in the Sloan Digital Sky Survey (SDSS) filters as (Gwyn, 2008):
LSST filters are the same as the SDSS photometry system (Ivezic et al., 2009; Fukugita et al., 1996). These magnitudes can also be transformed to the standard Johnson-Cousins photometry system333 http://www.sdss3.org/dr8/algorithms/sdssUBVRITransform.php. We do not simulate the magnitude of source stars in the band filter. The Besançon model does not give the magnitude of stars in this band. However, the LSST photometric uncertainty in this band is high, i.e., the 5 depth for point sources in band, , is whereas that for band is .
In order to determine the apparent magnitude of the source stars, we add the distance modulus and the extinction due to the interstellar gas and dust to the absolute magnitudes. We use the 3D extinction map presented by Marshal et al. (2006). They measured 3D extinction map for the Galactic latitude in the range of and the Galactic longitude in the range of with the step and the distance step . Then, we convert it to the extinction in band using (Marshall et al., 2006). The band extinction is converted to the extinction in other bands using Cardelli et al.(1989)’s relations. We assume of for Galactic bulge and for thin disk, thick disk, and the stellar halo (Nataf et al., 2013; Cardelli et al., 1989). We also add a Gaussian fluctuation to each extinction value with the width in the range depending on the wavelength (Cardelli et al., 1989). The source radius is estimated using the Stefan-Boltezman relation: , where is the source luminosity, is the effective surface temperature and is the Stefan-Boltzmann constant.
The blending effect in the LSST observations is significant, because this telescope is anticipated to detect stars as faint as those with in band. The number of such faint stars in the Galaxy is very high, which makes high blending effects for these faint stars. Therefore, it is crucial to consider and accurately calculate the blending amount for each source star. In order to calculate the contribution of background stars in the each LSST Point Spread Function (PSF), we calculate the averaged number of collinear stars toward the source line of sight whose light enters the PSF area which is given by:
where in square arcsec is the LSST PSF area for a typical source star. is the Full Width at the Half Maximum of the brightness profile due to a typical source star which is in arcsec unit corresponding to the filters , respectively. The is the total number density of stars in a given direction and at the distance from the observer, which is given by:
where is the mass density for the th structure of our galaxy, is the averaged mass amount for the th structure and the summation is done over different structures. The equation (2) gives the average number of blending stars and the true number in each measurement has a gaussian fluctuation around this value with the width . Figure 1 represents the map of in the Galaxy averaged over of observable microlensing events. For each of these blending stars, we calculate their apparent magnitudes as explained in the previous paragraph and as a result the overall flux due to all of blending stars, i.e., . One of these blending stars is the source star itself. The blending parameter is given by , where is the flux of the source star. In the real observation, if the overall magnitude due to all blending stars into a PSF reaches to the detection threshold, in that PSF one star is discerned, whereas in the simulation all of these blending stars pass the detectability criterion. In order to accordingly correct the simulation, we weight each simulated source star with its blending factor .
For the lens population, we first indicate the lens distance from the observer using the lensing probability function . According to the contribution of different structures in the total mass density at the location of the lens , we determine to which structure the lens belongs to. Then, the lens mass is chosen from the corresponding mass density function to the lens structure. The Besançon model provides separate mass functions for different structures. We assume both source and lens stars have global and dispersion velocities (Kayser et al., 1986; Binney & Tremaine, 2008). In order to determine the lens-source relative velocity, we (i) obtain the velocity components in the observer coordinate system which axes are parallel with and normal to the line of sight direction and (ii) after projecting the source velocity in the lens plane subtract each component of the lens and source velocities. In the Besançon model, the values of different components of dispersion velocities depend on the stellar age and structure. In the simulation, we discard the events with the Einstein crossing time shorter than or longer than days. The longer microlensing events are hard distinguish in real observations (see, e.g., Mróz et al., 2017; Wyrzykowski et al., 2015). The lens impact parameter is chosen uniformly from the range .
2.2. Generating synthetic data points
After generating the model microlensing events, the observability of their source stars by LSST is checked. From simulated model microlensing events, we ignore the microlensing events (i) which source stars are too faint to be detected at least in one of the LSST filters even when they are at the peak of their light curves and (ii) which source stars are fainter than the saturation limit of LSST in all filters. These events certainly are not observable. We had the detection threshold (i.e., limiting magnitude) for different LSST filters as given by Ivezic et al. (2009) (Table 2).
In order to test the observability of microlensing signatures of the remaining microlensing events, we generate the hypothetically data points taken by LSST and then verify if they can be discerned as microlensing events by exerting some criteria. The data points are simulated in the range , where is the Einstein crossing time, is the time of the closest approach that was uniformly chosen in the range of , where is the LSST lifetime. If the start time is less than zero (i.e., ) we start simulating data points from and if the end time is greater than we interrupt simulating data points on . The exposure time is fixed on . For timing the data points we also consider the seasonal gaps, i.e., the LSST observations happen only during about seven continuous months of each year. We assume that the weather is not suitable for the LSST observation with the probability of for each night. However, during each night, the uniform observation by LSST will take place with the probability of which is considered in the simulation.
For calculating the magnification factor, we consider the finite size effect of the source star and use the adaptive contouring algorithm (Dominik, 2007) to calculate the magnification while the lens distance from the source center is in the order of the source radius projected on the lens plane. The synthetic data points which are between saturation and detection limits of the LSST are considered. We ignore the microlensing parallax effect during magnification calculations.
We assume that the observed magnitude of each data point has a gaussian fluctuation with respect to model value with the width equal to expected photometric error filter (): . The contains the random and systematic photometric errors. We take into account these two uncertainties from Ivezic et al. (2009). For calculation we assumed sky brightness as given by Table 2 of the mentioned paper, i.e., ignoring impact of other stars and actual zenith distance. The photometric errors depend on wavelength and significantly decrease for the bright stars. In order to determine the epoch, airmass and filter used for taking each data point, we make a big ensemble of these parameters from Operations Simulator (OpSim) with the approved reference run minion444 https://www.lsst.org/scientists/simulations/opsim. Each data point is reported in one filter.
2.3. Detectability criteria
After generating synthetic data points of each model microlensing event, we probe if that event can be discerned. Our criteria for detectability are (i) there are at least consecutive data points (in any filter) with the observed magnification deviating from constant flux more than , (ii) the difference of from fitting the constant flux model and the microlensing model to the synthetic data points is larger than , and finally (iii) the peak of the light curve should be between and . As a result from the third criterion, we ignore the microlensing events for which the time of the closest approach is out of the LSST lifetime.
Six example simulated microlensing events with the synthetic data points are represented in Figures (2) and (3). The parameters used to make each of them are mentioned at the top of each light curve. is the baseline band brightness due to cumulative fluxes entered in the source PSF. The and are expressed in the days. The amounts of the background and intrinsic source flux depend on the filter used. We assume that these fluxes for each source star in all filters are measurable during the LSST observation. As a result, we can convert the measured magnitude in each filter to the corresponding magnitude in band and easily model all data points with one light curve, as shown in the figures.
The first microlensing event shown in Figure 2 is not detectable by LSST, because of high blending. The source star is magnified enough, but the blending causes the enhancement in the stellar brightness due to the lensing effect to shrink and become on the order of the photometric noise. The microlensing event shown in Figure 2 is not recognizable although it is a high-magnification event. Indeed, its time scale is too short in comparison with the LSST cadence so that only a single data point is taken during the magnification. The next event represented in Figure 2 is not detectable also, although there is no blending effect and the event’s time scale is long enough. Because of the seasonal gap, the peak of the light curve is not covered by the LSST data points.
The microlensing events shown in Figure (3) are observable by LSST. The first event has the large impact parameter, i.e., small lensing effect. Most microlensing events with small blending effect and the bright source stars can be detected. The next one (represented in Figure 3) is detected. In contrast to the high-magnification microlensing event 2 which was not detectable, this high-magnification event is detected. The duration of this event is long enough to take several data points while the source star is magnified. The last microlensing event shown in Figure 3 is also recognizable. The long-duration microlensing events have higher chance to be detected during the LSST lifetime in comparison to the short duration events.
Figures (2) and (3) show that the microlensing events of very faint source stars (specially those fainter than the LSST detection threshold) can not mostly be detected. These events need to be highly magnified to be detected, whereas the durations of high-magnification microlensing events are proportional to , mostly too short in comparison with the LSST cadence. Whereas, the microlensing events of bright source stars even with low magnification or long-duration ones are more likely to be detected. For these events the time scale of the magnification is of order of the Einstein crossing time, most likely long enough for taking several data points by LSST. In the next section we study the characteristics and statistical properties of the detectable microlensing events.
3. Observable Microlensing events with LSST
For each direction specified with the Galactic longitude and latitude with the steps , we perform a Monte Carlo simulation of microlensing events and probe their detectability, so that for every direction we have an ensemble of the detected events. In the following subsection we plot the map of characterizations and statistics of these events to study them. The numbers behind these maps are listed in Table (6) and (5) of the online version.
3.1. Characterizations and statistics
In Figure (4), we plot the maps of the averaged physical parameters of the lens and source stars for the observable microlensing events. These parameters are the source and the lens distances from the observer, the relative lens-source velocity, and the Einstein crossing time from top to bottom. Toward the small latitudes (), the interstellar extinction is very high which causes mostly the microlensing events with closer source and lens stars to be detectable, see Figure 4 and 4. According to Figure 4, toward the Galactic bulge excluding the points with most of the lens stars belong to the Galactic bulge and are located at the average distances around .
The Einstein crossing times of microlensing events far from the Galactic bulge are intrinsically much longer than those toward the Galactic bulge because the averaged relative lens-source velocity of the events far from the Galactic bulge is much smaller than that of the events toward the Galactic bulge, see Figures 4 and 4. For events that are far from the Galactic bulge on the sky, the relative lens-source velocity is smaller because the lens and source are close to each other and close to the Sun. Generally, the detectable microlensing events with LSST (due to long cadence) are a little longer than the detectable events with OGLE or MOA surveys toward similar lines of sight.
Figure (5) represents two maps: the top one, shows the blending parameter per line of sight averaged over the detectable microlensing events in -band. The blending parameter is a function of the stellar number density and decreases while increasing the stellar number density (plotted in Figure 1). In the bottom map, we plot the probability of discerning microlensing events which their source stars are visible at least at one filter toward a given direction, . For each line of sight, this probability is the fraction of the simulated microlensing events with detectable source stars (at least at one filter) which pass the detectability criteria (mentioned in the subsection 2.3). Generally, LSST detects the microlensing events with longer durations than typical values. Far from the Galactic bulge, the averaged Einstein timescale of microlensing events is longer than that of the events toward the Galactic bulge. On the other hand, the blending effect is ignorable toward the Galactic disk. These two effects make the probability function toward the Galactic plane be more than that toward the Galactic bulge.
For the statistics properties, we first calculate the overall optical depth due to all structures for the simulated microlensing events which are recognizable with LSST. The optical depth in given direction and distance can be calculated as (e.g., Moniez et al. (2017)):
where . Toward the Galactic disk, the distance of the detectable sources has a wide distribution. In that case the optical depth results from averaging over optical depths due to different source distances (Rahal et al., 2009). We consider the source stars are visible at peak (but not at baseline), the so-called DIA optical depth (Kerins et al., 2009), . The maps of the DIA optical depth is shown in Figures 6. The DIA optical depth is reduced in region due to the high extinction and blending, which prevent detection of events with sources at large distances.
Using the DIA optical depths, we estimate the observed event rate per line of sight as:
where is the LSST efficiency for detecting microlensing events with the duration toward a given direction. Indeed, this function is the mentioned probability function for special group of simulated microlensing events which have the timescale about . The efficiency function toward the Galactic bulge and the Galactic disk with is much smaller than those toward the other directions, because of their high blending effect and interstellar extinction, see Figure 5. In Figure (7), the LSST efficiency averaged over different directions versus the Einstein crossing time is plotted. This efficiency is calculated via a Monte-Carlo simulation over the whole Galactic plane. The efficiency function increases with increasing the Einstein crossing time. The event rate per line of sight through the Galaxy are represented in Figure 6. The event rate is high wherever the stellar number density is high, except the directions with , i.e., toward the Galactic disk with very high interstellar extinction.
Note. – For each direction, the averaged value of each parameter and its standard deviation from the mean value are mentioned in the first and second rows, respectively. and are calculated over the area .
In order to estimate the number of observable microlensing events, we evaluate the number of background and visible stars. Our criterion for visibility is that blended stellar brightness should be between LSST detection and saturation limits at least at one filter. The total number of these stars toward a given direction and per square degree is given by:
where is the efficiency for specifying stars located at a given distance toward a given direction at least at one LSST filter. We multiply by a factor of because around one third of stars are in binary systems and can not be discerned separately. Figure 6 shows the map of per square degree throughout the Galactic plane, which is very high toward the Galactic bulge in comparison with other directions. Because of the high extinction toward the Galactic disk () the number of visible stars reduces for these directions.
Finally, we can estimate the number of observable microlensing events per square degree during the observing time , using:
Figure 6 represents the map of per square degree per year in the logarithmic scale. The number of microlensing events toward the Galactic bulge and disk are in the order of and per square degree, respectively. Therefore, on the average the LSST fields toward the Galactic bulge and disk the number of events will be and , respectively during years observation with the cadence. Accordingly, LSST will detect very large number of microlensing events in comparison with the nowadays surveys because of (i) large FoV and (ii) its deep observations. Certainly, the probability of observing special events, e.g., the events with stellar black holes as microlenses, is high in large population of detected microlensing events.
In order to quantitatively compare the detectable microlensing events toward different directions in the Galaxy, in Table (1), we report the characteristics and statistics of these events for four different directions. The first column of this table specifies the Galactic latitude and longitude of these directions. The first direction is toward Baade’s window, the second one is toward the Sct ( which is one of four directions observed by EROS-II, the end of the Galactic bar is visible from this line of sight), other directions are toward the Galactic plane. In each row, the values of the physical parameters (first rows) and their standard deviations (second rows) calculated over the detectable microlensing events are reported. Two last columns are calculated over the area of the given line of sight, i.e., and . The number of visible stars per line of sight and the blending effect toward the Galactic bulge is higher than those toward the Galactic disk. As one can expect, the optical depth toward the Galactic bulge is higher than that toward the Galactic disk which causes the high number of detectable microlensing events toward the Galactic bulge. In the next subsection, we check the validity of our simulation by comparing with other microlensing observations.
3.2. Comparison of the LSST simulation with other observations
The EROS-II team has searched the microlensing events toward the Galactic spiral arms, away from the Galactic bulge (Rahal et al., 2009). Moniez et al. (2017) simulated the EROS-II observations and from comparing the real observations with the simulation constrained the kinematics of the disk, the stellar mass function and the maximum contribution of a thick disk in the form of the compact objects. In order to test our code by replicating the results of EROS-II, we repeat the simulation toward the four directions of EROS-II observations with the same conditions. Also, we use the function of the EROS-II efficiency for detecting microlensing events versus the Einstein crossing time (plotted in their Figure (6)) as the detectability function. Toward Sct with the coordinates we get the average value of the Einstein crossing time of days, which is in the agreement with the observed value of days. The quoted uncertainty is the standard deviation from the mean value. Toward Sct, , we get days, while the observed value was days. Toward Nor with , from simulation days, again in the same order of the observation amount, i.e. days. Finally, toward Mus with from simulation and observations are and days. The small differences between the results from our simulations and real observation are due to difference photometry systems for the source stars, their observing strategies, etc.
We also compare the optical depth map from this simulation with one resulted from Manchester-Besançon Microlensing Simulator (MaBlS)555http://www.mabuls.net/ which was developed by Awiphan et al. (2016). This simulation was based on the MOA-II observations of microlensing events. The map of the optical depth for DIA sources brighter than mag in -band (the faintest limit in their simulation) from MaBlS is shown in Figure 8 and our optical depth map in the same range of the Galactic latitude and longitude is plotted in Figure 8. These two maps are similar, but the optical depth from LSST simulation is larger than that from MaBLS. One reason is that LSST is deeper than mag in -band, even by considering the difference in their exposure times (the exposure time of MOA-II observations is seconds twice the LSST exposure which results the difference in their limiting magnitude diminishes by mag).
3.3. The impact of the LSST cadence on the Microlensing observation
In order to study the effect of improving the cadences on the microlensing detections with LSST, we perform the simulation with several cadences equal to days. In table (2), we report the physical parameters that depend on the cadence. These simulations are done for two directions toward (i) the Baade’s window with and (ii) the Galactic disk with . According to the table, improving the cadence makes the shorter-duration microlensing events due to somewhat fainter source stars be more observed. Since, the number of these events are intrinsically high, so by improving the cadence the number of detectable microlensing events raises. According to Table (2), changing the cadence from days to days doubles the number of observable microlensing events throughout the Galaxy.
4. LSST observing strategies
LSST is supposed to observe fields of the Galactic plane, i.e., with the coordinates and . Each field is almost circle-shape with the diameter and the area which corresponds to lines of sight in our simulations. of these fields will be observed by LSST with the cadence during years (I) and of these fields LSST will be observed only during the first year and with a cadence (II). These fields are shown in Figure (9). The fields will be observed with the cadence are represented with yellow circles and the others are shown with green ones.
Note. – Averaging is done over the detectable microlensing events toward different fields. The last column is the summation number of detectable events over all related fields.
Note. – A complete electronic version of this table is available at: ….
We used LSST OpSim simulations to extract epoch of observation, airmass, seeing FWHM, and filter for each visit in each field separately. These parameters have impact on the results of the simulation. We perform the Monte Carlo simulation for all of these fields to estimate the number of microlensing events that are detected by LSST by considering the corresponding their realistic strategies (I) and (II) and use the sequence of time, airmass, FWHM, filter for simulating syntectic data points for each simulated light curve. The table (3) contains the results of these simulations. The first row represents the characteristics of detectable microlensing events toward the fields shown with yellow circle in Figure (9) during years observations with the cadence and the second row, (II), shows the properties of the detectable microlensing events toward the other fields (green circle in Figure 9).
According to this table, LSST with the second strategy (II) will detect shorter-duration events than those are detectable with the first strategy (I). According to Figure (9), most of fields with small Galactic latitude (toward the Galactic bulge and disk) will be detected with the second strategy, whereas toward these directions the optical depth is higher. Consequently, the number of detectable microlensing events with the strategy (II) during one year with the cadence is more than those detected by the first strategy. Also, the stellar extinction for these directions is high which makes the averaged impact parameter of the detectable events be a little smaller. However, the microlensing events potentially detectable the strategy (II) will be of low value. The reasons are (i) the number of baseline data points is rare so that the source fluxes can not be estimated accurately. (ii) Lack of baseline data intensifies the degeneracy between the source flux and the Einstein crossing time which in turn causes weak estimations of the events’ timescale. During one year observation, (iii) measuring the parallax effect for long-duration microlensing events and (iv) discerning the variable stars from microlensing events are difficult. All of these issues can be solved by increasing the observational time to longer than one year.
Here, we compare these strategies in the regard of detecting microlensing events toward similar fields, by simulating detectable microlensing events. Table (4) contains some characteristic and statistic parameters of detectable microlensing events toward different fields by considering the LSST observing strategies (I) and (II) (the first and second values of each parameter are due to strategies I and II, respectively). This table can be used to optimize LSST observing strategy for disk microlensing events. As an example, when some of the fields currently scheduled for strategy (II) could be observed with strategy (I), one can select the bins of Galactic longitude and in each bin select a field for which the change of strategy would give the highest increase in . We note that the ratio of values for any given field in the two strategies is less dependent on simulation details than the raw values themselves. According to this table:
Generally, during years observation with epochs (I) LSST will detect more and on average longer microlensing events than those detectable during one year observation with epochs (II). Detecting longer microlensing events somewhat justifies the negative effect of long cadence in the observing strategy (I) on detection of short signals in microlenssing events, e.g., planetary ones. Usually, the longer microlensing events have longer planetary signals, because the time of caustic crossing is proportional to the Einstein crossing time. Hence, with the first observing strategy (I) although the time interval between data points is long and around days, but detectable events are on average longer and as a result have longer planetary signals.
With the second strategy (II) the probability of detecting microlensing events is higher than that with the other, because the number of short-duration microlensing events is intrinsically higher than long-duration ones. This cause that increasing the observing time from one year to years does not enhance the number of detectable events by a factor of .
Mostly, the source stars of detectable events with the strategy (I) are somewhat fainter with higher blending effect than those with the second strategy.
Accordingly, LSST can have significant sensitivity to exoplanets throughout the Galaxy, if either if cadence better than day is executed, or follow-up observations are conducted. By detecting planets toward different directions in the Galaxy, we can study their Galactic distribution (Gould, 2013).
5. Summary and conclusions
We studied the detection of microlensing events toward the Galactic disk and bulge with LSST. In this regard, we performed a Monte Carlo simulation according to its strategy toward the Galactic longitude and latitude in the ranges of and . We assumed that the cadence of the LSST observations is equal to days and its exposure time is seconds. The results of the simulation were
(i) LSST mostly detects the microlensing events of source stars with the average magnitude around in band. Although fainter stars (up to mag in this filter) are visible by LSST, but microlensing events due to these faint stars have small chance to be realized. Because of large blending effect they have to be highly magnified to generate high enough signal to noise ratios. But on the other hand, the high-magnification microlensing events’ durations are scaled by the lens impact parameters, i.e., their durations are mostly short in comparison to the LSST cadence.
(ii) Generally, the detectable microlensing events are (little) longer than common events observable with nowadays surveys. Thus, LSST partly helps to study microlensing events with more massive microlenses or closer events, etc.
(iii) We predicted that LSST on average detects around and microlensing events per square degree (or and per LSST’s FoV) during its lifetime toward the Galactic bulge and disk, respectively. This large number of visible microlensing events are due to its large FoV and its observing depth.
We performed some simulations with different cadences to study the effect of cadence on the statistics and properties of observable microlensing events. Our simulations show that improving the cadence increases the detection efficiency for short-timescale events. The number of these events is intrinsically high. Therefore improving the cadence raises the number of detectable microlensing events, e.g. improving the cadence from days to days approximately doubles the number of detectable microlensing events throughout the Galaxy.
The current strategy for LSST is that it observes (I) some parts of the sky with the average cadence during years and (II) some other parts of the sky with epochs during the first year of its lifetime. We performed the simulation by considering the corresponding strategies for these fields (shown in Figure 9) and concluded that the number of events corresponding to these strategies are and , respectively. Most of fields with small Galactic latitude (toward the Galactic bulge and disk) are supposed to be detected with the second strategy. Toward these directions, the stellar number density and as a results the optical depth and the event rate are higher which results the larger number of detectable microlensing events.
We have also presented expected number of events for each field under both observing strategies (Table 4) which could be used to optimize the LSST observing strategy. Toward alike field, LSST with first observing strategy (I) will detect more and on average longer microlensing events than those observable with the strategy (II). Although the cadence in the first strategy is long, but on the other hand long observing time ( years) helps carefully measuring the baseline source fluxes and the parallax effect for long events, discerning the variable stars from microlensing events, etc., whereas they are difficult to measure if only one year of observations is available. In addition, because of longer observing time the statistic of detectable events is higher with the first strategy than that with the second strategy.
Lastly, LSST can have significant role on detecting planets throughout the Galaxy and studying their Galactic distribution; either with the first strategy as well as follow-up observations or with the second strategy, i.e. day cadence or shorter, but with somewhat longer observing time. In addition, LSST Observation of the Galactic disk during several years with day cadence, first strategy (I), will allow finding isolated black holes. Long observing time helps to measure their parallax effects and baseline magnitudes, etc.
- Awiphan et al. (2016) Awiphan, S., Kerins, E., & Robin, A. C. 2016, MNRAS, 456, 1666
- Binney & Tremaine (2008) Binney, J., & Tremaine, S. 2008, Galactic Dynamics: Second Edition (Princeton University Press)
- Cardelli et al. (1989) Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245
- Dominik (2007) Dominik, M. 2007, MNRAS, 377, 1679
- Einstein (1936) Einstein, A. 1936, Science, 84, 506
- Fukugita et al. (1996) Fukugita, M., Ichikawa, T., Gunn, J. E., Doi, M., Shimasaku, K., & Schneider, D. P. 1996, AJ, 111, 1748
- Gould (2013) Gould, A. 2013, arXiv[astro-ph.GA]: 1304.3455
- Gwyn (2008) Gwyn, S. D. J. 2008, PASP, 120, 212
- Ivezic et al. (2009) Ivezic, Z., et al. 2009, in Bulletin of the American Astronomical Society, Vol. 41, American Astronomical Society Meeting Abstracts #213, 366
- Kayser et al. (1986) Kayser, R., Refsdal, S., & Stabell, R. 1986, A&A, 166, 36
- Kerins et al. (2009) Kerins, E., Robin, A. C., & Marshall, D. J. 2009, MNRAS, 396, 1202
- LSST Science Collaboration et al. (2017) LSST Science Collaboration et al. 2017, arXiv[astro-ph.IM]: 1708.04058
- Marshall et al. (2006) Marshall, D. J., Robin, A. C., Reylé, C., Schultheis, M., & Picaud, S. 2006, A&A, 453, 635
- Moniez et al. (2017) Moniez, M., Sajadian, S., Karami, M., Rahvar, S., & Ansari, R. 2017, A&A, 604, A124
- Mróz et al. (2017) Mróz, P., et al. 2017, Nature, 548, 183
- Nataf et al. (2013) Nataf, D. M., et al. 2013, ApJ, 769, 88
- Penny et al. (2017) Penny, M. T., Rattenbury, N. J., Gaudi, B. S., & Kerins, E. 2017, AJ, 153, 161
- Rahal et al. (2009) Rahal, Y. R., et al. 2009, A&A, 500, 1027
- Robin et al. (2012) Robin, A. C., Marshall, D. J., Schultheis, M., & Reylé, C. 2012, A&A, 538, A106
- Robin et al. (2003) Robin, A. C., Reylé, C., Derrière, S., & Picaud, S. 2003, A&A, 409, 523
- Wyrzykowski et al. (2015) Wyrzykowski, Ł., et al. 2015, ApJS, 216, 12
Note. – A complete electronic version of this table is available at: ….
Note. – A complete electronic version of this table is available at: ….


Scientists who use high-altitude scientific balloons have high hopes for their instruments in the future. Although the floating behemoths that carry their instruments far into the stratosphere can stay aloft for days on end, data collection typically happens during the night when starlight can be detected. The instruments that operate during the day are limited in their field of view due to overbearing sunlight.
An engineer at NASA's Wallops Flight Facility (WFF), located on Virginia's Eastern Shore, is working on a low-cost, off-the-shelf solution to overcome the challenges of collecting data in daylight.
Under WFF's Balloon Program, engineer Scott Heatwole and his team are developing a precision attitude sensor or star tracker that would be able to locate points of reference, or in other words, stars, during daylight hours. These points of reference serve as landmarks that help orient the instrument so that it can find the target of interest.
The star tracker is being developed specifically for the Wallops Arc Second Pointer (WASP), which would use the star tracker's data to point a balloon-borne scientific payload with incredible accuracy and stability. Currently, WASP usually employs the commonly used ST5000 star tracker. However, this device cannot image in the daytime even at 120,000 feet where scientific balloons operate. Though relatively dark at those altitudes, the scattering of sunlight off the atmosphere can overwhelm the starlight in most star cameras.
"A precision attitude sensor capable of working in the daylight would extend science operations through the day which would significantly increase the amount of science collected," Heatwole said. "Currently, the only precision attitude sensor available in daytime is a sun sensor, and this isn't ideal because it provides only two axes of attitude and is not precise over a range of targets across the sky."
Although others have developed custom star trackers that enable around-the-clock science gathering, no one has pulled together an inexpensive, ready-to-go package that includes cameras, computers, and the algorithms necessary to process data and eliminate excess visible light in real time. "That's what we're trying to do," Heatwole said, adding that his daytime star tracker consists of a commercial firewire camera attached to a lens and baffle that help filter out visible light, allowing it to sense points of reference in the near-infrared wavelength bands.
In 2014, a prototype of the device flew on two WASP missions. The first, the flight of the HyperSpectral Imager for Climate Science (HySICS) collected radiance data as WASP pointed the instrument toward the Earth, the sun, and the Moon. The goal was to see what the star tracker saw at 120,000 feet.
The second WASP mission, launched a couple months later in October, carried the Observatory for Planetary Investigations from the Stratosphere (OPIS). Its mission was to gather time measurements of Jupiter's atmospheric structure -- a challenge for the new star tracker because the gas giant is a bright object.
"Our algorithm didn't work as we had hoped," Heatwole said, adding that it did not filter out the excess light as expected.
Heatwole, however, is unfazed. Over the coming months, he plans to fine-tune the algorithms to eliminate the extra light experienced during the OPIS mission and then retest the technology during a sounding rocket flight this summer and additional WASP missions in 2016 and 2017.
"We're trying to increase the capabilities of WASP," Heatwole explained. "No company is going to go out and build this. No one is going to develop an off-the-shelf, low-cost daytime star tracker and put all the components in one package. WASP requires an attitude sensor that is capable in the daytime. That's what we hope to create."
For more Goddard technology news, visit:
Lori Keesey | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Earth Sciences
19.07.2018 | Power and Electrical Engineering
19.07.2018 | Materials Sciences


Calibration of the Hubble Space Telescope polarimetric modesStellar and galactic polarimetry from space is an unexplored observational regime and one which holds exciting promise for answering many fundamental astrophysical questions. The Hubble Space Telescope will be the first space observatory to provide a variety of polarimetric modes to astronomers including spectral, imaging, and single-aperture UV polarimetry. As part of the calibration program for these modes, the Space Telescope Science Institute has initiated a ground-based program to define faint standard fields and solicited community support to establish a temporal baseline for these potential standard targets. In this paper, the polarimetric capabilities of the Hubble Space Telescope, the philosophy and complications of in-flight calibration, and the status and direction of the standard targets program are discussed.
Lupie, O. L. (Space Telescope Science Inst. Baltimore, MD, United States)
Stockman, H. S. (Space Telescope Science Institute Baltimore, MD, United States)


Unlocking the Secrets of the Universe 3-11
Throughout history humans have gazed in awe at the starry vault overhead. But for millenniums the enormity and significance of what they saw were veiled to them, veiled by the limitations of their eyesight, their superstitions, and their presumptuousness. Now, by means of optical telescopes and radio telescopes and other devices, many secrets of the universe are being unlocked. On the cover of this magazine is a photo of the Trifid Nebula. Inside it, new stars have been born.
Economic Anxieties—When Will They End? 13
The bad news is: As long as greedy commerce holds its grip on the masses, economic anxieties will continue. The good news is: Its grip will soon be broken.
What Is This Thing Called Intuition? 16
What is its source? Is it the sole province of women, or do men also possess it?
[Picture Credit Line on page 2]
Cover photo: D. F. Malin, courtesy of Anglo-Australian Telescope Board


New Manual 5-Position Filter Wheel
8 November 2012 | Steve
Some consider a filter wheel to be an astro-imaging accessory but filter wheels are used by visual observers too. Consider, you could load a number of visual filters into the wheel then simply dial them into the field of view. It beats manually moving a filter from eyepiece to eyepiece when changing magnification, so less chance of it dropping onto the patio! You could fit a Moon filter (or two with different densitys) a light-pollution-reduction filter, a UHC, fringe-killer or whatever other visual filter you find most useful. One compartment can be left empty for unfiltered viewing.
This simple manual filter wheel will hold up to five 1.25" filters in threaded, numbered, compartments. The filter wheel can be attached to your focuser either by the supplied 1.25” nosepiece adaptor or via a T-thread.
The robustly constructed wheel is supplied with a 1.25” eyepiece adaptor, 1.25” focuser nosepiece, T-2 camera adaptor and locking ring.
Please note: your focuser will require 20mm of inward focusing distance from the normal focus position to compensate for the thickness of the filter wheel.


Re: Mars Curiosity Rover... to land 10:31 pm 8/5/2012
^ Stay up. You don't need to go to work tomorrow.
Rimmer, on what period of history to live in-
“Well, It’d be the 19th century for me, one of Napoleon’s marshals.
The chance to march across Europe with the greatest general of all time and kill Belgians” - (White Hole).


Please use this identifier to cite or link to this item:
|Title:||Thermal evolution of the Kramer radiating star||Authors:||Govender, Megandhren
Maharaj, S. D.
Lorton, L. B.
|Keywords:||Schwarzschild solution;Gravitational collapse;Heat ﬂow||Issue Date:||Jan-2016||Publisher:||Springer Link||Source:||Govender, M. et al. 2016. Thermal evolution of the Kramer radiating star. PRAMANA - Journal of Physics. 86(1): 49-58.||Abstract:||The Kramer radiating star uses the interior Schwarzschild solution as a seed solution to generate a model of dissipative collapse. We investigate the thermal behaviour of the radiating star by employing a causal heat transport equation. The causal temperature is explicitly determined for the ﬁrst time by integrating the transport equation. We further show that the dissipation of energy to the exterior space-time renders the core more unstable than the cooler surface layers.||URI:||http://hdl.handle.net/10321/2950||ISSN:||0304-4289 (print)
|Appears in Collections:||Research Publications (Applied Sciences)|
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The John Glenn Astronomy Park (JGAP) is dedicated to sparking an interest in science, learning, and exploration by sharing with visitors the wonders of the sky, both day and night. If you have an interest in the night sky and the beauty of the stars, certainly check out the JGAP while you’re in the hills.
About The John Glenn Astronomy Park
The building of an astronomy park in the Hocking Hills State Park was inspired by our ever-vanishing view of the night sky in modern urban settings. The Hocking Hills, in rural southeastern Ohio, is one of the few areas left in the state of Ohio where the night sky can be seen clearly without being obscured by light pollution from the cities. The observatory provides a venue for visitors to the Hocking Hills State Park to experience the night sky through a large telescope and with their eyes.
The observatory also draws on the countless generations of humans who marked the important changes of the seasons through the motion of the sun and who built great structures, like Stonehenge in England, the Chaco Canyon Kiva in New Mexico or many Hopewell and Fort Ancient Earthworks in Ohio, that commemorated these days. The plaza has been designed to allow the rays of the sun to fall upon a special central point on the first day of each of the four seasons.
“The greatest thing we can do is inspire young minds…”
– JOHN GLENN
The JGAP is named for John Glenn, an inspiring man who was a military pilot, US Senator for Ohio, and famously the first American astronaut to orbit the Earth.
Visiting the John Glenn Astronomy Park
The JGAP is open all hours of the day all year long, and is completely free to the public. Visiting the John Glenn Astronomy Park is a beautiful experience at any time of the day. When you visit the park at night, you will have access to their 28-inch telescope in the roll-off roof observatory or the option to set up your own telescope and gear. If the moon, planets, stars, and galaxies are within view, you are sure to see them! Night programs begin at sunset.
If you visit the park during the day, you’ll get to look out at the Earth’s closest star: the sun. JGAP’s telescopes are outfitted with special filters so you can view the sun during the day for a whole new view of our solar powerhouse. Plus, you can learn all about the solar system at the exhibits and activities found around the park.
For more information about the John Glenn Astronomy Park,
including information on donating to the non-profit that operates the park, visit jgap.info.


Star Cluster Westerlund 2 and Starforming Nebula Gum 29
This image from the Hubble Space Telescope shows a giant cluster of about 3,000 stars called Westerlund 2. The cluster resides inside a vibrant stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina. The comparatively young, 2-million-year-old star cluster contains some of our galaxy's hottest, brightest, and most massive stars. The largest stars are unleashing a torrent of ultraviolet light and hurricane-force winds that etch away the enveloping hydrogen gas cloud. This creates a fantasy celestial landscape of pillars, ridges, and valleys.
The Hubble Space Telescope just passed the 25th anniversary of its launch on April 24, 1990 and continues to operate at the peak of its capabilities.
Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota
(ESA/STScI), and the Westerlund 2 Science Team


Can the universe really be as weird as quantum theory suggests? Ingenious experiments are coming close to settling the issue
WHEN Rupert Ursin stood in the darkness at the highest point of La Palma in the Canary Islands he found it scary. “Really scary,” he says. It was less the blackness stretching out towards the Atlantic Ocean some 15 kilometres away. It was more the sheer technical challenge ahead- and perhaps just a little because of the ghosts he was attempting to lay to rest.
Ursin and his colleagues from the Institute for Quantum Optics and Quantum Information in Vienna, Austria, were there that night to see if they could beam single photons of light to the 1-metre aperture of a telescope on the island of Tenerife, 144 kilometres away. Even on a fine day, when Teide, Tenerife’s volcanic peak, is clearly visible from La Palma, that would be a


This THEMIS image captures a portion of several lava flows in Daedalia Planum southwest of the Arsia Mons shield volcano. Textures characteristic of the variable surface roughness associated with different lava flows in this region are easily seen. The lobate edges of the flows are distinctive, and permit the discrimination of many overlapping individual flows. The surfaces of some flows look wrinkly and ropy, probably indicating a relatively fluid type of lava flow referred to as pahoehoe. The surface textures of lava flows can thus sometimes be used for comparative purposes to infer lava viscosity and effusion rates. Numerous parallel curved ridges are visible on the upper surfaces of some of the lava flows. These ridges make the flow surface look somewhat ropy, and at smaller scales this flow might be referred to as pahoehoe, however, these features are probably better referred to as pressure ridges. Pressure ridges form on the surface of a lava flow when the upper part of the flow is exposed to air, cooling it, but the insulated much warmer interior of the flow continues to move down slope (and more material is pushed forward from behind), causing the surface to compress and pile up like a rug.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.


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For several years, I have been conducting what has become the most comprehensive forensic investigation into the validity of the Apollo lunar landing program and the National Aeronautics and Space Administration ever carried out before - and I am now ready to begin showing the world what they have been missing.
Originally posted by Electro38
Why did the USSR not protest or reveal the hoax.
Originally posted by QBSneak000
Well my friend, a great find indeed!! star and flag!!
There has got to be a way to somehow photograph from earth, the structures and other secrets on the moon that NASA has kept from the public for years.


BAIKONUR /Kazakhstan/, September 21. /TASS/. The cooperation on the ISS project will depend on the International Space Station’s technical condition, and will highly likely continue until 2028, Roscosmos CEO Yuri Borisov said Wednesday.
"We plan [to work at the station] through 2024, and then we will continue depending on the ISS’ condition. Highly likely, until 2028," Borisov said during a press conference after the Soyuz MS-22 spacecraft’s docking.
According to the Roscosmos CEO, Russia always strictly fulfills its international obligations. On Wednesday, negotiations with NASA representatives took place at the Baikonur Cosmodrome.
On July 28, Borisov said during the meeting with Russian President Vladimir Putin that the decision on Russia’s withdrawal from the ISS project after 2024 has been made, adding that all obligations before the partners will be fulfilled. On July 29, Borisov explained on Russian TV that the exact date of Russia’s withdrawal from the ISS program will depend on the station’s condition.


“Geminids over Gates Pass”
What an incredible show we had here in Tucson, Arizona! This was definitely the best show of the year. I was able to see about 50 per hour! We were fortunate enough to have clear skies on the first Peak night on 12-12-12 through the morning of 12-13-12 but the desert had other, rainy plans for the best peak night.
Everlasting Productions hired me to shoot some time-lapses of this incredible event for their documentary…and I am sure glad they did! I mean…I would’ve shot it anyway, but, they loaned me their Canon 5DMKIII to shoot with! I’ve been wanting to try this beast out and I absolutely loved it. And to top that…they let me use their Carl Zeiss glass! I got some pretty sharp images with it. Time to start saving.
I may put together a short 1 minute video so you can see what the Geminids had to show, so stay tuned!
Anyways, here are some composites of about 30 frames from a time-lapse I shot of the Geminid Meteor shower at Gates Pass in Tucson, Arizona on the morning of 12-13-12. You can see M31 (Andromeda Galaxy 2.5million light years away) at the left next to the Milky way.
These imagse took a lot of work as I had to scroll through about 400 frames and find which frames had shooting stars in them, then cut out every meteor and blend.
Space.com used my photo on their Geminid Meteor shower write-up!
Earthsky.org also used my image in their daily news!
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Sharing is Appreciated!
Carl Zeiss 21mm F/2.8 Distagon
ISO 3200, 20 seconds.
If you’d like to purchase or use this photo please email Sean@Sean-Parker.com


Sculpted by stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed the shape of a horse. Fittingly named the Horsehead Nebula, light from it takes about 1,500 light-years to reach us.
It is embedded in the vast Orion cloud complex within the Orion constellation. Although the constellation is easily visible in the evening sky towards the south, it is very difficult to see the Horsehead Nebula through the telescope, as a large telescope and dark skies are required.
About five light-years “tall”, the dark cloud is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434 in the background.
The gigantic gas clouds making up the Horsehead Nebula have been captured excellently by Leonard Ellul-Mercer in this colour image shot by the skilful use of astronomical cameras through his telescope.
Also known as Barnard 33, the unusual shape was first…
View original post 166 more words


Although, yes, you should just keep them until the eclipse in the US in 2024 (or the one in the Andes in 2019, which I haven’t completely ruled out just yet, because I’ve become a crazy person), there’s another good reason to keep a pair or two handy:
More specifically: GIANT sunspots!
Right now, there are two fairly-large sunspot areas on the face of the sun. They’re so big, in fact, that they can be seen without magnification. Just put on your eclipse glasses and take a gander. Both of them are pretty close to the center of the solar disk, as seen by the picture above (which is from late yesterday). These will continue to rotate left-to-right across the face of the sun over the next several days.
Take a look; this is pretty cool (bonus points if you work in an office and go out and stand in the parking lot looking up at the sun for no apparent reason).
My favorite site to keep up on this sort of thing is spaceweather.com. Our “space weather” is almost-entirely affected by the sun, so most things on the site lean that way. If civilization as we know it is about to be ended by another Carrington Event, this will be one of the early places to hear about it.
Quick note about eclipse glasses. Although I heard a few mixed reports about whether or not eclipse glasses would degrade over time and therefore only be safe to use for the next few years, this appears to not be the case:
Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 standard adopted in 2015.
So, keep track of those things, as long as you’ve got good ones.


- Create your own projector with this amazing astronomy kit that includes a 4.5-inch diameter lamp, star charts, and more.
- Four cardboard panels fold and mold around the small light device. Switch it on and projections of both northern and southern hemispheres shine brightly on the walls for hours of observation and study.
- Now you can invite your friends to enjoy the star show in the comfort and convenience of your own living room.
- Give the gift of science with toys and gadgets that foster curiosity and encourage scientific learning.
- Recommended for ages 3 and up.
- Challenge your child's imagination with 4M toys and kits.
- 4M educational toys cover a wide range of educational subjects and include science kits, arts and crafts kits, robotics kits, and more.
4M Create A Night Sky Projection Kit


The incredible sparking soil on the MOON: NASA reveals solar storms can cause 'miniature lightning strikes'
- Study found sparks occur in frigid, permanently shadowed regions near poles
- May possibly produce 'sparks' that could vaporize and melt the soil
- Could have as much effect on the surface as a meteoroid impact
Powerful solar storms can produce sparks on the moon's surface, NASA has revealed.
A new study has found the sparks occur in the frigid, permanently shadowed regions near the lunar poles, and may possibly produce 'sparks' that could vaporize and melt the soil.
NASA said it could have as much effect on the surface as a meteoroid impact.
Scroll down for video
A new study has found the frigid, permanently shadowed regions near the lunar poles, and may possibly produce 'sparks' that could vaporize and melt the soil. . Nasa said it could have as much effect on the surface as a meteoroid impact, affecting up to 10% of the soil. This is a map showing the permanently shadowed regions (blue) that cover about three percent of the moon's south pole.
THE CHANGING MOON
The moon has almost no atmosphere, so its surface is exposed to the harsh space environment.
Impacts from small meteoroids constantly churn or 'garden' the top layer of the dust and rock, called regolith, on the moon.
'About 10 percent of this gardened layer has been melted or vaporized by meteoroid impacts,' said Andrew Jordan of the University of New Hampshire, Durham.
'We found that in the moon's permanently shadowed regions, sparks from solar storms could melt or vaporize a similar percentage.'
Jordan is lead author of a paper on this research published online in Icarus August 31, 2016.
Explosive solar activity, like flares and coronal mass ejections, blasts highly energetic, electrically charged particles into space.
Earth's atmosphere shields us from most of this radiation, but on the moon, these particles - ions and electrons - slam directly into the surface.
They accumulate in two layers beneath the surface; the bulky ions can't penetrate deeply because they are more likely to hit atoms in the regolith, so they form a layer closer to the surface while the tiny electrons slip through and form a deeper layer.
The ions have positive charge while the electrons carry negative charge. Since opposite charges attract, normally these charges flow towards each other and balance out.
In August 2014, however, Jordan's team published simulation results predicting that strong solar storms would cause the regolith in the moon's permanently shadowed regions (PSRs) to accumulate charge in these two layers until explosively released, like a miniature lightning strike.
The PSRs are so frigid that regolith becomes an extremely poor conductor of electricity.
Therefore, during intense solar storms, the regolith is expected to dissipate the build-up of charge too slowly to avoid the destructive effects of a sudden electric discharge, called dielectric breakdown.
The research estimates the extent that this process can alter the regolith.
'This process isn't completely new to space science -- electrostatic discharges can occur in any poorly conducting (dielectric) material exposed to intense space radiation, and is actually the leading cause of spacecraft anomalies,' said Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Maryland, a co-author of the paper.
The team estimated the energy that would be deposited over a million years by both meteoroid impacts and dielectric breakdown driven by solar storms, and found that each process releases enough energy to alter the regolith by a similar amount.
What's happening: Frigid, permanently shadowed regions near the lunar poles, and may possibly produce 'sparks' that could vaporize and melt the soil.
'Lab experiments show that dielectric breakdown is an explosive process on a tiny scale,' said Jordan.
'During breakdown, channels could be melted and vaporized through the grains of soil.
'Some of the grains may even be blown apart by the tiny explosion.'
The next step is to search for evidence of dielectric breakdown in PSRs and determine if it could happen in other areas on the moon.
There may even be 'sparked' material in the Apollo samples, but the difficulty would be determining if this material was altered by breakdown or a meteoroid impact.
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Can gas escape from a very large gravity grasp? Black Hole Are you forming a “tsunami” in space?
In a new NASA-funded study, astrophysicists used computer simulations to model the environment around a supermassive black hole in deep space. They discovered that a huge tsunami-like structure could have formed near these black holes.They even think of it Supermassive black hole You can host the largest tsunami-like structure in the universe.
“It’s the laws of physics that can explain things here in space and even far outside black holes,” said Daniel Proga, an astrophysicist at the University of Nevada, Las Vegas (UNLV). It was. Said in a NASA statement..
In this study, researchers explored the strange environment around a supermassive black hole and how gas and radiation interact there.
Supermassive black holes have large disks of gas and matter that swirl around them and over time. Active galactic nucleus.. These systems often emit a jet of matter, emitting bright, glowing x-rays onto a disc that is out of the reach of gravity in a black hole. This X-ray radiation pushes the wind flowing from the center of the system. This is called a “spill”.
this X-ray radiation Researchers also believe that it may help explain the denser gaseous regions in the environment around supermassive black holes called “clouds.”
“These clouds are ten times hotter than the surface of the sun and move at the speed of the solar wind, so they are exotic objects that you don’t want to fly,” said lead author Dr. Tim Waters. UNLV, a guest scientist at the Los Alamos National Laboratory in New Mexico, said in the same statement.
In computer simulations, the team showed how the atmosphere of a disk rotating around a black hole begins to form waves of gas and material when it is far enough away from the black hole and out of reach. With the addition of outflows pushed out by X-ray radiation, these waves can grow into huge tsunamis.These swirling gas waves can extend up to 10 Light year On the disc, the researchers found it. Once these tsunami-like structures are formed, they are no longer affected by black holes. gravity, According to the statement.
In these simulations, researchers showed how bright X-ray radiation near a black hole penetrates into a pocket of hot gas outside the disk. These hot plasma bubbles expand to nearby cooler gases at the edge of the disc, helping to spur tsunami-like structures. Bubbles also block outflowing wind and swirl into separate structures up to light-year size. These lateral structures are known as the Karman vortex streets. This is a weather pattern that also occurs in the following locations: Earth (On Earth, this pattern of swirling vortices Looks quite different.. )
The Kalman Vortex Street is named after the Hungarian-American physicist Theodore von Kalman. Earth’s atmosphere And space.
According to the statement, this study goes against previous theories suggesting that clouds of hot gas near active galactic nuclei form spontaneously due to fluid instability. This study also contradicts the previous notion that a magnetic field is needed to move colder gas from the disc around a supermassive black hole.
Currently operating satellites cannot confirm their work, but the team hopes to enhance their findings with future research and hopefully telescope observations.Furthermore, observation of plasma near the active galactic nucleus of NASA Chandra X-ray Observatory And of the European Space Agency XMM-Newton According to a NASA statement, the space telescope is in line with the team’s findings.
This work Released on June 15 It is published in the Astrophysical Journal.
Send an email to Chelsea Gohd to email@example.com or follow her on Twitter @ chelsea_gohd. Follow us on Twitter @ Spacedotcom and Facebook.
Supermassive black holes can host huge swirling gas “tsunamis”
Source link Supermassive black holes can host huge swirling gas “tsunamis”


The astronomy picture of the day is Laniakea, the newly discovered/defined super-structure that includes our Milky Way Galaxy. There’s already a Wikipedia entry. The massive Virgo Supercluster is now just an “appendage” in the bigger scheme of things.
It’s hard to discern shape when you’re sitting within. The thing I’ve never heard referenced is how astronomers map structure taking into account the tens and hundreds of millions of years between one end and another. Not just big space, but long stretches of time.
We’re on one side of Laniakea, but we view the other side not as it is today, but as it was almost five hundred million years ago. All galaxies are in movement relative to each other. Most are flying apart. Only close associations share a gravitational attraction. Astronomers admit the boundaries of superclusters are vague. We know, for example, the Triangulum Galaxy, imaged here by Alexander Meleg …
… is gravitationally bound to our Local Group. It’s a probable satellite of the Andromeda Galaxy. We might be colliding with that whole array in a few billion years. But will our star stuff be mixing it up with aliens on the other side of Laniakea in the endless eons to come? Who can be sure?


The spacecraft lasted more than 50 times longer than originally planned, delivering groundbreaking science and inspiring a generation
Published By @EMPIREGENIUS
After more than 14 years driving across the surface of Mars, the NASA rover Opportunity has fallen silent—marking the end of a defining mission to another world.
At a press conference at the Jet Propulsion Laboratory in Pasadena, California, NASA bid farewell to the rover it placed on Mars on January 25, 2004: before Facebook, before the iPhone, and even before some of the scientists now in charge of it graduated high school. In its record-breaking time on Mars, the rover drove more than 28 miles, finding some of the first definitive signs of past liquid water on the red planet’s surface.
“With this mission, more than other robotic missions, we have made that human bond, so saying goodbye is a lot harder. But at the same time, we have to remember this phenomenal accomplishment—this historic exploration we’ve done,” says John Callas, the project manager for the Mars Exploration Rovers mission. “I think it’ll be a long time before any mission surpasses what we were able to do.”
NASA had not heard from the rover since June 2018, when one of the most severe dust storms ever observed on Mars blotted out much of the red planet’s sky and overtook the solar-powered rover. Initially, the storm didn’t give the team pause. From about November to January, the red planet saw seasonal winds strong enough to wipe accumulated dust from Opportunity’s solar panels, which is one of the major reasons the rover lasted so long in the first place. But when “rover cleaning” season came and went without signals from Opportunity, hopes that it had survived began to dim
On January 25, the team sent Opportunity a set of last-ditch commands, hoping that the rover had fallen silent because of malfunctioning antennae and an internal clock on the fritz. But the commands meant to fix this admittedly unlikely scenario didn’t wake the rover.
Now, as Martian fall and winter overtake it, NASA says that the rover will remain forever paused halfway down a windswept gully, named Perseverance Valley for the rover’s dogged effort.
The announcement marks the end of the record-smashing Mars Exploration Rovers mission, which built and operated Opportunity and its sibling rover, Spirit. The two rovers were each designed to go less than a mile and last 90 to a hundred Martian days, or sols. But the pair surpassed every conceivable expectation. After landing on January 4, 2004, Spirit drove hard through rugged terrain until it got stuck in 2009 and went silent in 2010. Meanwhile, Opportunity went farther for longer than any other vehicle on another world—and all other Mars rovers combined.
“It was one heck of a mission, wasn’t it?” Mike Seibert, a former driver of Opportunity, says in an email. “I am looking forward to the future when Opportunity’s records fall, because that will mean that we continue to explore our solar system. And I look forward to congratulating the team that puts Opportunity into second place.” (See amazing pictures from 20 years of nonstop rovers on Mars.)
“I always felt that were really two honorable ways for a mission like this to end,” adds Cornell planetary scientist Steve Squyres, the mission’s longtime principal investigator. “One is simply that we wear the vehicles out. The other is Mars just finally reaches out and kills them. To have Opportunity go for 14-and-a-half years and then get taken out by one of the most ferocious Mars dust storms in decades—if that’s the way it plays out, we can walk away with our heads held high.”
Published By @EMPIREGENIUS


See the amazing photos from the Expedition 61 crew on the International Space Station in our full gallery here!
SpaceX successfully conducted an in-flight abort test of its Crew Dragon crew capsule on Jan. 19 to test the emergency escape system for astronauts. See photos of the test here!
If you haven't signed up for the Space.com forums yet, now is a great time, as there's a ton of things to get involved in.
The astronauts of Expedition 61 have tackled some historic spacewalks at the International Space Station, including the first all-woman spacewalk and four of the most challenging spacewalks ever.
The 237th meeting of the American Astronomical Society will unveil the latest discoveries in space and the future of astronomy.
It's shopping season, space fans, so here's a round-up of the best deals online for out-of-this-world telescopes, toys and more.
We've scoured the web for Lego sets that are space or science-themed, as well as many science-fiction-themed sets.
Pete Conrad and Alan Bean make a jolly, blind, pinpoint lunar landing and grab rock samples revealing the Moon's strange birth.
With the return of the Space.com forums, we're hosting an AMA with NASA JPL's Charles White, aka the "Space Pope."
Space.com is relaunching our space community forums as we celebrate our 20th anniversary. Welcome back and let's talk some space!
Elon Musk founded SpaceX primarily to help humanity settle Mars, and here's a look at how he plans to do it — a giant rocket called Super Heavy and a 100-passenger vehicle called Starship.
Private rocket company SpaceX is a leader among the new space push to send humans to orbit on commercial craft.
NASA's Apollo program put the first humans on the moon. See how the missions flew in this photo tour.


Context. The thermal conductivity of highly porous dust aggregates is a key parameter for many subjects in planetary science; it is not yet fully understood, however. Aims. We investigate the thermal conductivity of fluffy dust aggregates with filling factors lower than 10-1. Methods. We determined the temperature structure and heat flux of the porous dust aggregates calculated through N-body simulations of static compression in the periodic boundary condition. Results. We derive an empirical formula for the thermal conductivity through the solid network ksol as a function of the filling factor of dust aggregates φ. The results reveal that ksol is approximately proportional to φ2, and the thermal conductivity through the solid network is significantly lower than previously assumed. In light of these findings, we must reconsider the thermal histories of small planetary bodies.
- Comets: general
- Radiative transfer


Multiple codes are available to derive atmospheric parameters and individual chemical abundances from high-resolution spectra of AFGKM stars. Almost every spectroscopist has its own preferences regarding which code and method to use. But intrinsic differences between codes and methods lead to complex systematics that depend on multiple variables such as the selected spectral regions and the radiative transfer code used. I expanded iSpec, the popular open source spectroscopic tool, to support the most known radiative transfer codes and I assessed their similarities and biases when using multiple setups based on the equivalent width method and the synthetic spectral fitting technique (interpolating from a pre-computed grid of spectra or synthesizing with interpolated model atmospheres). This work shows that systematics on atmospheric parameter and abundances between most of the codes can be reduced when using the same method and a careful spectral feature selection is executed, but it may not be possible to ignore the remaining differences depending on what is the scientific case and the required precision. Regarding methods, equivalent width-based and spectrum fitting-analyses exhibit large differences that emerge due to their intrinsic differences, which is relevant given the popularity of these two methods. The results help us identify the key caveats of modern spectroscopy that any scientist should be aware of before trusting its own results or being tempted to combine atmospheric parameters and abundances from the literature.


Volume 378, Number 3, November II 2001
|Page(s)||1067 - 1077|
|Section||Planets and planetary systems|
|Published online||15 November 2001|
Coordinated observations of the quiet Sun transition region using SUMER spectra, TRACE images and MDI magnetograms
Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
Accepted: 20 August 2001
The relationship between the transition region ultraviolet emission and the underlying magnetic field is explored through a detailed analysis of SUMER Siiv line profiles, TRACE Civ, continuum and 171 Å intensities, and MDI high resolution magnetic field measurements. The observations track a narrow area of quiet Sun near disk center over a period of 3 hours. Highly variable emission is found throughout. The most dramatic line Doppler shift and brightness variations come from a region of complex field evolution. The brightenings sometimes have faint elongated extensions in the TRACE Civ images. In most events with high Doppler shifts, the Siiv line wing reveals plasma flow 1-2 min before the line core brightens which suggests that plasma acceleration precedes plasma compression and/or heating. Simultaneous measurement of transition region densities using Oiv line ratios imply large density fluctuations in the transition region plasma. There is an indication of waves of compression and rarefaction crossing the spectrometer's field-of-view. The waves' speed across the solar surface is between 20-40 km s-1, and the compression may be as high as 10. In space-time images density fluctuations are much more prevalent and conspicuous than brightenings. In several cases the waves seem to start at the position of Siiv brightenings.
Key words: Sun: magnetic fields / Sun: transition region / Sun: UV radiation
© ESO, 2001
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