In astronomy, luminosity is not quite the same thing as brightness. Luminosity measures the total amount of energy emitted</u/l> by a star or other astronomical object in SI units of joules per second, which are watts. A watt is one unit of power, and just as a light bulb is measured in watts, so is the Sun, which has a total power output of 3.846×10 W. This number is the basic metric used in astronomy: it is known as 1 solar luminosity, the symbol for which is formula_1.
Radiant power, however, is not the only way to conceptualize brightness, so other metrics are also used. The most common is apparent magnitude, which is the perceived brightness of an object from an observer on Earth at visible wavelengths. Other metrics are absolute magnitude, which is an object's intrinsic brightness at visible wavelengths, irrespective of distance. The measure of luminosity is "bolometric magnitude", the total power output across all wavelengths.
Star formation
Star formation means the earliest stages in a star's life. Dense regions of particles exist in molecular clouds known as "stellar nurseries". The clouds collapse under gravitation into spheres of plasma to form stars.
High density regions of the interstellar medium (ISM) form clouds, or "nebulae", where star formation takes place.
In the dense nebulae where stars are produced, much of the hydrogen is in the molecular (H) form, so these nebulae are called molecular clouds. The largest such formations, giant molecular clouds, have densities of 100 particles per cm, diameters of , and masses up to 6 million solar masses, and an average interior temperature of 10 K. About half the total mass of the galactic ISM is found in molecular clouds. In the Milky Way there are about 6,000 molecular clouds, each with more than 100,000 solar masses. The nearest nebula to the Sun where massive stars are being formed is the Orion nebula, away. However, lower mass star formation is occurring about 400–450 light years distant in the ρ Ophiuchi cloud complex.
A more compact site of star formation is the opaque clouds of dense gas and dust known as Bok globules; so named after the astronomer Bart Bok. The Bok globules are typically up to a light year across and contain a few solar masses. They can be seen as dark clouds against bright emission nebulae or background stars. Over half the known Bok globules have been found to contain newly forming stars.
A spiral galaxy like the Milky Way contains stars, the remains of stars (stellar remnants) and a diffuse interstellar medium (ISM) of gas and dust. The interstellar medium consists of 10 to 10 particles per cm usually of about 70% hydrogen by mass, with most of the remaining gas consisting of helium. This medium is chemically enriched by trace amounts of heavier elements that were ejected from stars as they passed beyond the end of their main sequence lifetime.
In contrast to spirals, an elliptical galaxy loses the cold component of its interstellar medium within about a billion years. This hinders the galaxy from forming diffuse nebulae except through mergers with other galaxies.
This is a massive protostar about 300 times brighter than our Sun. Astronomers have caught a key stage in the birth of a very heavy star. They used two radio telescope views of the process 18 years apart. The young star is 4,200 light-years from Earth and is surrounded by a doughnut-shaped cloud of dust.
The first observation was in 1996. By 2015 its stellar wind changed from a compact spherical form to a larger, ionized elliptical shape. This gave information about what happens as a massive star forms. Being able to observe its rapid growth is unique, according to Huib van Langevelde of Leiden University, one of the authors of a study of the object.
Indulkana Range
The Indulkana Range is a range of hills in the northwest of South Australia. It is sometimes called the Mount Chandler Range after its highest peak. It is located to the southwest of Indulkana, on the Aṉangu Pitjantjatjara Yankunytjatjara lands. The mountains of the Indulkana area are part of the traditional country of the Yankunytjatjara and Antakarinya.
The range consists of a series of parallel ridges running east to west. The southern side of the range ends in an escarpment, the most prominent point of which is Chambers Bluff. The rock is made up of quartzite and sandstone rock, resting on slates of kaolinised clay. At the eastern end of the range is Mount Chandler, which overlooks the settlement of Indulkana and the Indulkana Creek. It rises about from its base. It is made up of quartzite, quartz sandstone and sandstone. Slightly north of the escarpment, and following its path from east to west, is a series of gorges that split the hills. The gorges contain several reliable springs.
Hydrazone
A hydrazone is the functional group with structure RRC=NNH. They are like aldehydes or ketones, with an NNH group instead of the oxygen atom.
They are made by reacting hydrazines with ketones or aldehydes:
Hydrazones are very useful molecules to do some reactions. For example, a ketone can be reduced down completely if made into a hydrazine and then treated with sodium ethoxide (Wolff–Kishner reduction). Hydrazones are very important intermediates in many reactions, such as the Fischer indole synthesis. This makes indoles, groups which are found in many drugs.
Protest the Hero
Protest the Hero are a Canadian progressive metal band from Whitby, Ontario.
Protest the Hero was formed in 2001 under the original name, Happy Go Lucky. They changed their name to Protest the Hero the next year and recorded their first EP, "Search for the Truth".
The band released their debut full-length album "Kezia" on August 30, 2005 in Canada and on April 4, 2006 in the United States. They released their second studio album "Fortress" on January 29, 2008. Their third studio album "Scurrilous" was released on March 16, 2011 in Japan and on March 22, 2011 in both Canada and the Unites States. The band announced that they were releasing their fourth studio album in Summer 2013. The band said that the album would be crowdfunded through Indiegogo. The album had a fundraising goal of $125,000 and was reached within 30 hours. The band eventually reached $341,146 in fundraising which nearly tripled their original set goal.
Reaction intermediate
A reaction intermediate or simply intermediate is a molecule that is formed during a chemical reaction. It is not the final product, but it is something that is more like the product than the reactants. After every step in a reaction mechanism, an intermediate is formed.
Intermediates usually stay around for a little time because they are very reactive. However, it is important not to confuse an intermediate with a transition state. The latter is at a point of maximum energy. An intermediate instead is at a point of minimum energy, i.e. it is a stable molecule. Intermediates can be isolated from a reaction if needed.
For example, in the reaction:
A + B → X → C + D
X is the intermediate. In going from A + B to X and from X to C + D, the reaction will go through a transition state.
Gulf of Aqaba
The Gulf of Aqaba (, transliterated: ') or Gulf of Eilat (, transliterated: ') is a wide gulf between the Sinai Peninsula in Egypt and west of the Arabian Peninsula in Saudi Arabia. The gulf is an extension of the Red Sea. It is long and wide. At this northern end of the Gulf are three cities: Taba in Egypt, Eilat in Israel, and Aqaba in Jordan.
Erythema ab igne
Erythema ab igne is a rash of the skin, which is usually caused by the long-term exposure to heat or infrared radiation, and which is not a burn. Usually the name is abbreviated "EAI". Other names include hot water bottle rash fire stains, laptop thigh, granny's tartan and toasted skin syndrome.
Some people may complain of mild itchiness and a burning sensation. When a change in skin pigmentation can not be seen, it is often not noticed at all.
Ayalon River