omnianasa/nasa-apod-metadata huggingface dataset:
A Leonid Meteor Explodes (1998-11-23)
Click on the above image and watch a Leonid meteor explode.  The tremendous heat generated by the collision of a small sand-bit moving at 70 kilometers/second with the Earth's upper atmosphere causes the rock-fragment to heat up, glow brightly, and disintegrate.  In some cases, the meteor literally explodes leaving a visible cloud that dissipates slowly.  The above image shows just such an explosion for a bright meteor from the recent Leonid Meteor Shower.  Clicking on the above image will start a (4.2 Megabtye) movie of thirty 1-minute exposures showing the explosion cloud dissipate.  Each movie frame, taken with the ROTSE telescope early 17 November, is 8 degrees across - 16 times the diameter of the full moon.  Near the middle of the sequence, a less bright meteor moves through the field.
Seven Leonids Over Wise Observatory (1998-11-24)
More Leonids were visible at some places than others.  In Israel, early in the morning of 17 November, it rained meteors though a clear sky.  Observers there reported a peak rate for the 1998 Leonid Meteor Shower of about 600 meteors per hour.  Visible in the above picture are no fewer than seven Leonid meteors occurring over just a few minutes.  (Can you find them all?)  The dome of the Wise Observatory is visible on the right.  The Earth's rotation causes stars to appear as arcs. The 1998 Leonids might be remembered not for their numbers, however, but for the unusually high fraction of bright fireballs.  Another eventful Leonid Meteor Shower is forecast for the same time next year.
A Leonid Bolide Over Kansas (1998-11-25)
Tomorrow's picture: Meteor Sky  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC &: Michigan Tech. U.
Meteor Milky Way (1998-11-26)
The bold, bright star patterns of Orion (right) are a familiar sight to even casual skygazers. But this gorgeous color photo also features a subtler spectacle - the faint stars of the Milky Way. A broad region of the Milky Way runs vertically through the picture with the striking red Rosette Nebula in bloom left of center. Cutting across this dim, diffuse band of stars which lie along the plane of our Galaxy is a meteor streak. It seems to pass just under the red-orange giant star Betelgeuse at Orion's shoulder. Astrophotographer Jeff Medkeff recorded this and other beautiful time exposures from a dark sky countryside southeast of Sierra Vista, Arizona USA, during November's Leonid meteor shower.
Twisting Meteor Train (1998-11-27)
Blazing through the sky at 70 kilometers per second, 100 kilometers or so above planet Earth, many bright Leonid meteors left behind a persistent, smoke-like trail of glowing, hot, ionized gas. Twisting in high altitude winds, these trails or trains typically were visible for many minutes. As Iowa astrophotographer Tom Bailey captured the eerie, wispy remains of this persistent train from a fireball arcing overhead, yet another fainter Leonid meteor flashed across the sky.
A Lonely Neutron Star (1998-11-28)
How massive can a star get without imploding into a black hole?  These limits are being tested by the discovery of a lone neutron star in space. Observations by the Hubble Space Telescope have been combined with previous observations by the X-ray ROSAT observatory and ultraviolet EUVE observatory for the isolated star at the location of the arrow.  Astronomers are able to directly infer the star's size from measurements of its unblended brightness, temperature, and an upper limit on the distance. Assuming that the object is a neutron star of typical mass, some previous theories of neutron star structure would have predicted an implosion that would have created a black hole. That this neutron star even exists therefore allows a window to the extreme conditions that exist in the interiors of neutron stars.
Arecibo: The Largest Telescope (1998-11-29)
The Arecibo radio telescope is currently the largest single-dish telescope in the world.  First opening in 1963, this 305 meter (1000 foot) radio telescope resides in a natural valley of Puerto Rico. The Arecibo telescope has been used for many astronomical research projects, including searches and studies of pulsars, and mapping atomic and molecular gas in the Galaxy and the universe. As the Arecibo dish can also be used to send radio waves, it has bounced and recorded radiation off of planets in our Solar System, and has even broadcast messages to areas of the Galaxy that might contain intelligent extra-terrestrial life. Any person in the world may use the telescope, providing their proposal is selected by a review committee.
An Annotated Leonid (1998-11-30)
The 1998 Leonids Meteor Shower was perhaps the most photographed meteor event in history.  Patient observers saw bright meteors streak across dark skies every few minutes, frequently leaving fading trails stretching across the sky.  High above the Anza-Borrego Desert, a meteor was photographed streaking up from the radiant constellation of the Leonids: Leo.  This meteor train covered over 40 degrees, and changed colors from green to red.
Cepheus 1: Nearby Galaxy Hiding (1998-12-01)
Some galaxies are hard to find.  Besides being hidden behind the dust and bright foreground stars of our Milky Way Galaxy, recently discovered Cepheus 1 was missed previously because it is so uniformly dim.  In fact, the first indication that any galaxy was there at all came in the radio band from the Dwingeloo radio telescope in the Netherlands.  Close inspections of optical photographs like the one above then revealed Cepheus 1 as the low-surface brightness galaxy in the center.  Cepheus 1 turns out to be only about 20 million light years distant, and so is one of the few spiral galaxies that live close by.  Low-surface brightness (LSB) galaxies like Cepheus 1 are still being studied, but are known to have relatively large separations between bright stars, and to be more commonly found away from other galaxies.
A Deep Field In The Southern Sky (1998-12-02)
This new deep view of the cosmos is the sequel to the 1995 hit Hubble Space Telescope Deep Field. Billed as the Hubble Deep Field South, it was produced by pointing the space telescope toward a patch of sky in the southern constellation Tucana. Over a period of 10 days, many separate exposures were accumulated and combined to reveal progressively fainter galaxies. The original deep field was constructed by observing a piece of sky in the northern constellation Ursa Major. Both stare down 12 billion light-year long tunnels to far-off and still mysterious times when young galaxies inhabited an infant universe. Hubble Deep Field South observations were released to an enthusiastic audience on November 23, 1998.
Deep Space 1 (1998-12-03)
Going gently into the night, Deep Space 1's ion drive has been running smoothly since it was restarted on November 24. How powerful is this high-tech spacecraft's ion propulsion system? At full throttle the engine will consume about 2,100 watts of electrical power generated by solar panels and produce about 1/50th of a pound of thrust. This is roughly equivalent to the force you exert when holding up a single sheet of paper! While clearly not suitable for vehicles which need rapid acceleration, ion propulsion is advantageous to use for missions involving asteroid and comet rendezvous. For these long space voyages which ultimately require a lot of energy, the continuous, gentle nudge of an ion engine easily wins out over brief, powerful, but less efficient blasts from chemical rockets. Pictured here during ground tests, the Deep Space 1 craft is now about three million miles from planet Earth.
Centaurus A: The Galaxy Deep Inside (1998-12-04)
Deep inside Centaurus A, the closest active galaxy to Earth, lies ... another galaxy! Cen A is a giant elliptical galaxy a mere 10 million light-years distant with a central jumble of stars, dust, and gas that probably hides a massive black hole. This composite combines an optical picture of Cen A with dark lines tracing lobes of radio emission and an infrared image from the ISO satellite (in red). The ISO data maps out the dust in what appears to be a barred spiral galaxy about the size of the prominent nearby spiral M33. The discoverers believe that the giant elliptical's gravity helps this barred spiral galaxy maintain its shape. In turn, material funneled along the spiral's bar fuels the central black hole which powers the elliptical's radio lobes. This apparently intimate association between two distinct and dissimilar galaxies suggests a truly cosmic symbiotic relationship.
Surveyor Hops (1998-12-05)
This panorama of the cratered lunar surface was constructed from images returned by the US Surveyor 6 lander. Surveyor 6 was not the first spacecraft to accomplish a soft landing on the Moon ... but it was the first to land and then lift off again! After touching down near the center of the Moon's nearside in November of 1967, NASA controllers commanded the spacecraft to hop. Briefly firing its rocket engine and lifting itself some 4 meters above the surface, the Surveyor moved about 2.5 meters to one side before setting down again. The hopping success of Surveyor 6 essentially marked the completion of the Surveyor series main mission - to determine if the lunar terrain was safe for the planned Apollo landings.
CG4: A Ruptured Cometary Globule (1998-12-06)
The odd looking "creature" to the right of center in the above photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails.  These features cause cometary globules to have visual similarities to comets, but in reality they are very much different.  Cometary globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not completely known. The galaxy to the left of center is very far in the distance and is only placed near CG4 by chance superposition.
Star-Forming Region RCW38 (1998-12-07)
Star cluster RCW38 was hiding. This open cluster of stars is located about 5000 light years away towards the constellation of Vela.  Looking there will not normally reveal most of the stars in this cluster, though. The reason is that the open cluster is so young that it is still shrouded in thick dust that absorbs visible light.  This dust typically accompanies the gas that condenses to form young stars.  When viewed in infrared light, however, the star cluster in RCW38 is revealed, because dust is less effective at absorbing infrared light.  The above photograph was one of the first ever taken with the new Infrared Spectrometer and Array Camera (ISAAC) affixed to the 8.2-meter Very Large Telescope.
Leonids from Leo (1998-12-08)
Is Leo leaking? Leo, the famous sky constellation visible on the left of the above all-sky photograph, appears to be the source of all the meteors seen in this year's Leonids Meteor Shower.  That Leonids point back to Leo is not a surprise - it is the reason this November meteor shower is called the Leonids.  Sand-sized debris expelled from Comet Tempel-Tuttle follows a well-defined orbit about our Sun, and the part of the orbit that approaches Earth is superposed in front of the constellation Leo.  Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Leo.  Over 150 meteors can be seen in the above four-hour exposure.  The Geminid Meteor Shower, which appears to eminate from the constellation of Gemini, peaks this coming weekend.
NGC 253: The Sculptor Galaxy (1998-12-09)
NGC 253 is not only one of the brightest spiral galaxies visible, it is also one of the dustiest.  Discovered in 1783 by Caroline Herschel in the constellation of Sculptor, NGC 253 lies only about ten million light-years distant.  NGC 253 is the largest member of the Sculptor Group of Galaxies, the nearest group to our own Local Group of Galaxies.  The dense dark dust accompanies a high star formation rate, giving NGC 253 the designation of starburst galaxy.  Visible in the above photograph from the Hubble Space Telescope is the active central nucleus, also known to be a bright source of X-rays and gamma rays.
Assembling The International Space Station (1998-12-10)
Batteries and solar panels were included with this version of the International Space Station (ISS) but some assembly is still required. On Saturday, December 5th, the STS-88 crew of the Space Shuttle Endeavor achieved the in orbit docking of the Zarya and Unity (foreground) ISS modules. On Monday, astronauts James Newman (left) and Jerry Ross continued the assembly procedures connecting power and data cables during the first of three planned spacewalks. Ground controllers were then able to successfully activate the ISS. Now orbiting planet Earth at an altitude of about 248 miles, Endeavour and the ISS are reported to be in excellent shape and crew members plan to enter the new space station today. Five Americans, one Russian, and the Unity module itself were lifted into orbit by the shuttle on Friday, December 4, while the Zarya (sunrise) module was launched on a Proton rocket from the Baikonur Cosmodrome in Kazakstan on November 20.
High Redshift Quasars (1998-12-11)
ch red speck indicated above is a powerful quasar estimated to be over 100 times brighter than a galaxy. Yet in these Sloan Digital Sky Survey discovery images the quasars appear faint because they are extremely distant. Their distances have been indirectly gauged by noting how much the light they emit has been stretched to longer wavelengths by the expansion of the Universe. Because red light has the longest wavelengths in the visible spectrum, this stretch has come to be called "redshift" - the greater the distance, the greater the redshift. Astronomers use a number known as "Z" to quantify this cosmological redshift and the quasar at the left, with a Z of 5, was just proclaimed the new quasar redshift champion (from left to right the measured Zs are 5.00, 4.90, 4.75). What's the actual distance to quasars with Zs of 5 or so? ... about 15 billion light-years, give or take a few billion light-years depending on your favorite cosmology!
Driving To The Sun (1998-12-12)
How long would it take to drive to the Sun? Brittany, age 7, and D.J., age 12, ponder this question over dinner one evening. James, also age 7, suggests taking a really fast racing car while Christopher, age 4, eagerly agrees. Jerry, a really old guy who is used to estimating driving time on family trips based on distance divided by speed, offers to do the numbers. "Let's see ... the Sun is 93 million miles away. So, if we drove 93 miles per hour the trip would only take us 1 million hours." How long is 1 million hours? One year is 365 days times 24 hours per day, or 8,760 hours. One hundred years would be 876,000 hours, still a little short of the 1 million hour drive time -- so the Sun is really quite far away. Christopher is not impressed, but as he grows older he will be. You've got to be impressed by something that's 93 million miles away and still hurts your eyes when you look at it!
Blasting Off from the Moon (1998-12-13)
How did the astronauts get back from the Moon? The Lunar Module that landed two astronauts on the Moon actually came apart. The top part containing the astronauts carried additional rocket fuel which allowed it to blast away, leaving the bottom part on the Moon forever. The top part would later meet up with the Command Module and its astronaut pilot, which were continually orbiting the Moon. All would then return to Earth together. The above picture was taken by a robot TV camera left on the Moon by the crew of Apollo 16.  The frame above captures the top part of the Lunar Module just at it was blasting off.
The Hubble Deep Field South (1998-12-14)
Among the faintest objects are some of the most unusual objects. The Hubble Deep Field South was released after much anticipation earlier this month, delivering a unique view of some of the most distant parts of our universe. Part of this field is shown above.  Numerous astronomers are currently poring over this field, trying to find clues about young galaxies, cosmological curvature, and dark matter.  Clearly, visible among galaxies as dim as magnitude 30 in this long-duration exposure (and in the original Hubble Deep Field North) are many peculiar looking galaxies. One interesting artifact is the blue arc just to the upper right of the large galaxy near the image center.  This arc may be light from a more distant galaxy focused by the gravitational lens effect of the nearer galaxy.
Plains and Ridges on Europa (1998-12-15)
The ridges on Europa may be caused by cold water volcanoes.  Europa, one of the largest moons of Jupiter, has been the source of intense scrutiny since speculation increased of there being oceans beneath its icy surface.  Currently the Galileo spacecraft orbiting Jupiter is on an extended mission designed, in part, to study Europa's surface in greater detail.  The above image highlights features common to Europa's surface: pure blue water ice beneath lighter ridges that run for many kilometers.  These ridges may result from volcanic cracks in the ice where emerging liquid water froze upon exposure to the cold of deep space.  The reasons for the colors of the ridges remain uncertain.
3-D Mars' North Pole (1998-12-16)
This dramatic premier three-dimensional visualization of Mars' north pole is based on elevation measurements made by an orbiting laser. During the Spring and Summer of 1998 the Mars Orbiter Laser Altimeter (MOLA) flashed laser pulses toward the Martian surface from the Global Surveyor spacecraft and recorded the time it took to detect the reflection. This timing data has now been translated to a detailed topographic map of Mars' north polar terrain. The map indicates that the ice cap is is about 1,200 kilometers across, a maximum of 3 kilometers thick, and cut by canyons and troughs up to 1 kilometer deep. The measurements also indicate that the cap is composed primarily of water ice with a total volume of only about four percent of planet Earth's Antarctic ice sheet. In all it represents at most a tenth of the amount of water some scientists believe once existed on ancient Mars. Where did all the water go?
The Night Shift (1998-12-17)
For the orbiting International Space Station (ISS), the sun sets every 90 minutes. But working through the night, spacewalking astronauts can rely on artificial lighting. Here, the eerie glow of work-lights illuminate Space Shuttle Endeavor astronaut Jerry Ross during a night on his second spacewalk as he continues the in orbit assembly of the ISS. Endeavor landed at Kennedy Space Center Tuesday night bringing an end to the successful ISS assembly mission and the final shuttle mission of 1998.
TT Cygni: Carbon Star (1998-12-18)
TT Cygni is a cool red giant star with a wind. This false-color picture of TT Cyg was made using a coordinated array of millimeter wavelength radio telescopes and shows radio emission from carbon monoxide (CO) molecules in the surrounding gas. The central emission is from material blown off the red giant over a few hundred years while the thin ring, with a radius of about 1/4 light-year, actually represents a shell of gas expanding outward for 6,000 years. Carbon stars like TT Cyg are so named for their apparent abundance of carbon containing molecules. The carbon is likely the dredged-up ashes of nuclear helium burning in the stellar interior. Carbon stars loose a significant fraction of their total mass in the form of a stellar wind which ultimately enriches the interstellar gas - the source of material for future generations of stars. TT Cyg is about 1,500 light-years away in the constellation Cygnus.
Cartwheel Of Fortune (1998-12-19)
By chance, a collision of two galaxies has created a surprisingly recognizable shape on a cosmic scale - "The Cartwheel Galaxy". The Cartwheel is part of a group of galaxies about 500 million light years away in the constellation Sculptor (two smaller galaxies in the group are visible on the right). Its rim is an immense ring-like structure 100,000 light years in diameter composed of newly formed, extremely bright, massive stars. When galaxies collide they pass through each other, their individual stars rarely coming into contact. However, the galaxies' gravitational fields are seriously distorted by the collision. In fact, the ring-like shape is the result of the gravitational disruption caused by a small intruder galaxy passing through a large one, compressing the interstellar gas and dust and causing a a star formation wave to move out from the impact point like a ripple across the surface of a pond. In this case the large galaxy may have originally been a spiral, not unlike our own Milky Way, transformed into the wheel shape by the collision. But ... what happened to the small intruder galaxy?
Edge-On Spiral Galaxy NGC 891 (1998-12-20)
Is our Galaxy this thin? We believe so. The Milky Way, like NGC 891 pictured above, has the width of a typical spiral galaxy. Spirals have most of their bright stars, gas, and obscuring dust in a thin disk.  This disk can be so thin the spiral galaxy appears edge-on like a compact disk seen sideways. The dark band across the middle is a lane of dust which absorbs light.  Some of the billions of stars that orbit the center of NGC 891, however, appear to be moving too fast to just be traveling in circles.  What causes this peculiar motion?  One hypothesis is that NGC 891 has a large bar across its center -- a bar that would be obvious were we to see this galaxy face-on instead of edge-on. This false color picture was constructed from 3 near infrared images.
Solstice Sun In Soft X-rays (1998-12-21)
The solstice occurs today at 8:56 PM Eastern Standard Time. At the solstice the sun reaches its most southerly position in the sky and winter begins for the Northern Hemisphere while summer starts South of the Equator. This false-color image of the sun was made about 48 hours before the solstice in the light of soft (lower energy) X-rays by a telescope on board the space-based Yohkho solar observatory. The normally bright, visible solar surface or photosphere appears dark in X-ray light while active regions in the solar corona which lie above the photosphere are particularly X-ray bright. Solar photospheric temperatures are about 6,000 degrees C. but the X-ray bright coronal regions have temperatures of millions of degrees. Why is the sun's corona so hot?
Dawn of the Leonids (1998-12-22)
Many of the 1998 Leonid shower meteors were so bright they could be seen even during sunrise.  The above photograph was taken near the dawn of November 16 close to Hong Kong, China.  However, most meteors are fainter and are not associated with any particular meteor shower.  On any given night from a dark location it would not be unusual to see up to 10 meteors per hour,  while the predictable Meteor showers might feature 100 meteors per hour.  A true meteor storm will occur only a few times per century.  The actual intensity of meteor storms is notoriously hard to predict, but may feature rates upwards of 10 meteors per second.
Ring Around the Galaxy (1998-12-23)
It is difficult to hide one galaxy far behind another.  The closer galaxy's gravity will act like a huge lens, pulling images of the background galaxy around both sides.  This is just the case observed in the above recently released image from the VLT: the red galaxy in the middle is in the foreground, lensing the image of the background green galaxy into surrounding contorted arcs.  These images are more than sideshows, since the distance between background images increases with the mass of the lens.  This lens mass turns out to be much greater than the sum of all its stars - indicating the presence of dark matter.  The distorted galaxy is said to appear as an Einstein ring, named after Albert Einstein who accurately predicted many attributes of the gravitational lens effect -- although he also guessed that such an effect was unlikely to be seen in practice.