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Altair is a main sequence star.

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This Hubble Space Telescope image shows Sirius A, the brightest star in our nighttime sky, along with its faint, tiny stellar companion, Sirius B. Astronomers overexposed the image of Sirius A so that the dim Sirius B (tiny dot at lower left) could be seen. The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system. The two stars revolve around each other every 50 years. Sirius A, only 8.6 light-years from Earth, is the fifth closest star system known.

Credit: NASA, H.E. Bond and E. Nelan (Space Telescope Science Institute, Baltimore, Md.); M. Barstow and M. Burleigh (University of Leicester, U.K.); and J.B. Holberg (University of Arizona)

Main sequence stars fuse hydrogen atoms to form helium atoms in their cores. About 90 percent of the stars in the universe, including the sun, are main sequence stars. These stars can range from about a tenth of the mass of the sun to up to 200 times as massive.

Stars start their lives as clouds of dust and gas. Gravity draws these clouds together. A small protostar forms, powered by the collapsing material. Protostars often form in densely packed clouds of gas and can be challenging to detect.

"Nature doesn't form stars in isolation," Mark Morris, of the University of California at Los Angeles (UCLS), said in a statement. "It forms them in clusters, out of natal clouds that collapse under their own gravity."

Smaller bodies - with less than 0.08 the sun's mass - cannot reach the stage of nuclear fusion at their core. Instead, they become brown dwarfs, stars that never twinkle. But if the body has sufficient mass, the collapsing gas and dust burns hotter, eventually reaching temperatures sufficient to fuse hydrogen into helium. The star turns on and becomes a main sequence star, powered by hydrogen fusion. Fusion produces an outward pressure that balances with the inward pressure caused by gravity, stabilizing the star.

How long a main sequence star lives depends on how massive it is. A higher-mass star may have more material, but it burns through it faster due to higher core temperatures caused by greater gravitational forces. While the sun will spend about 10 billion years on the main sequence, a star 10 times as massive will stick around for only 20 million years. A red dwarf, which is half as massive as the sun, can last 80 to 100 billion years, which is far longer than the age of the universe. (This long lifetime is one reason red dwarfs are considered to be good sources for planets hosting life, because they are stable for such a long time.)

Bright shining star

In the early 20th century, astronomers realized that the mass of a star is related to its luminosity, or how much light it produces. These are both related to the stellar temperature. Stars 10 times as massive as the sun shine more than a thousand times as much.

The mass and luminosity of a star also relate to its color. More massive stars are hotter and bluer, while less massive stars are cooler and have a reddish appearance. The sun falls in between the spectrum, given it a more yellowish appearance.

This understanding lead to the creation of a plot known as the Hertzsprung-Russell (H-R) diagram, a graph of stars based on their brightness and color (which in turn shows their temperature). Most stars lie on a line known as the "main sequence," which runs from the top left (where hot stars are brighter) to the bottom right (where cool stars tend to be dimmer). [Video: Constructing the Hertzsprung-Russell Diagram (Hubble site)]

When the stars go out

Eventually, a main sequence star burns through the hydrogen in its core, reaching the end of its life cycle. At this point, it leaves the main sequence.

Stars smaller than a quarter the mass of the sun collapse directly into white dwarfs. White dwarfs no longer burn fusion at their center, but they still radiate heat. Eventually, white dwarfs should cool into black dwarfs, but black dwarfs are only theoretical; the universe is not old enough for the first white dwarfs to sufficiently cool and make the transition.

Larger stars find their outer layers collapsing inward until temperatures are hot enough to fuse helium into carbon. Then the pressure of fusion provides an outward thrust that expands the star several times larger than its original size, forming a red giant. The new star is far dimmer than it was as a main sequence star. Eventually, the sun will form a red giant, but don't worry - it won't happen for a while yet.

"Some five billion years from now, after the sun has become a red giant and burned the Earth to a cinder, it will eject its own beautiful nebula and then fade away as a white dwarf star," Howard Bond, of Space Telescope Science Institute in Maryland, said in a statement.

If the original star had up to 10 times the mass of the sun, it burns through its material within 100 million years and collapses into a super-dense white dwarf. More massive stars explode in a violent supernova death, spewing the heavier elements formed in their core across the galaxy. The remaining core can form a neutron star, a compact object that can come in a variety of forms.

The long lifetime of red dwarfs means that even those formed shortly after the Big Bang still exist today. Eventually, however, these low-mass bodies will burn through their hydrogen. They will grow dimmer and cooler, and eventually the lights will go out.

Additional resources

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Main Sequence Stars: Definition & Life Cycle

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Main sequence stars fuse hydrogen atoms to form helium atoms in their cores. About 90 percent of the stars in the universe, including the sun, are main sequence stars. These stars can range from about a tenth of the mass of the sun to up to 200 times as massive.

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It is about 1.7 times bigger than the sun.

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Altair is 16.7 light years from the earth.

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A light year is the distance that light travels in one year. The year used by the International Astronomical Union is 365.25 days. Therefore a light year is exactly 9,460,730,472,580.8 kilometers.

A mile is a unit of distance equal to 5,280 feet or exactly 1.609344 kilometers. It is commonly used to measure the distance between places in the United States and United Kingdom.

Light Years to Miles Conversion Table

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A light year is the distance that light travels in one year. The year used by the International Astronomical Union is 365.25 days. Therefore a light year is exactly 9,460,730,472,580.8 kilometers. A mile is a unit of distance equal to 5,280 feet or exactly 1.609344 kilometers.

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Helium Hydrogen and Dust

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Norm Klekoda
(Dark Skies Michigan;
used with permission)

Altair is the bright star at
left of the dark nebula.
(See a2MASS Survey
image of Altair from the
NASA Star and Exoplanet
Database.)

System Summary

The name Altair is derived from the Arabic for "The Flying Eagle." The star is located about 16.7 light-years (ly) away from our Sun, Sol, in the north central part (19:50:47.00+08:52:05.96, ICRS 2000.0) of Constellation Aquila, the Eagle. Also called Alpha Aquilae, Altair is the brightest star in Aquila. It is also the lower left member of the " Summer Triangle" of first magnitude stars viewed from the northern hemisphere, formed with Vega (Alpha Lyrae) at the lower right, and Deneb (Alpha Cygni) at upper right. Altair is readily visible to the naked eye. With a telescope, an optical companion may be visible. (See Akira Fujii's color photo of Altair -- brightest bluish star at the top center of photo.)

NASA Observatorium

See a discussion of
the "main sequence"
as part ofstellar
evolution and death.

The Star

Altair is a white main sequence dwarf star of spectral and luminosity type A7 V-IVn. According to various estimates, the star has about 1.7 times Sol's mass ( RECONS), 1.8 times its equatorial diameter ( JPL press release, 2001; T. Moon, 1985; Morossi and Malagnini, 1985, page 369; and Johnson and Wright, 1983, page 695), and about 10.7 times its visual luminosity and 9.845 its bolometric luminosity ( NASA Star and Exoplanet Database, derived from of Kenneth R. Lang, 1980). Like Sirius, however, Altair radiates much more in ultraviolet wavelengths than Sol, and, not surprisingly, the European Space Agency has used ultraviolet spectral flux distribution data to determine stellar effective temperatures and surface gravities, including those of Altair.

Steve Golden/NASA/JPL/Caltech/Mount Wilson Observatory

Altair is14 percent wider than it is tall (seevideo).

Based on Altair's abundance of iron, the star appears to be twice as enriched as Sol with elements heavier than hydrogen ("metallicity"), ( Cayrel de Strobel et al, 1991, page 306). Not surprisingly, dust has been detected around this young star ( Kuchner et al, 1998 -- in pdf). According to Holweger et al (1999), this dust disk may have developed after most of the surrounding nebulae of gas has been absorbed or expelled as a shell of gas from the developing star before it reached the main sequence.

Altair has the New Suspected Variable designation NSV 24910 and is unusually bright for its spectral type and so may be becoming a subgiant star that is beginning to evolve off the main sequence, as it begins to fuse the increasing amounts of helium "ash" mixed with hydrogen at its core. Although the star should be only a few hundred million years old, it is so much bigger and hotter than Sol that it will exhaust its core hydrogen around only a billion years and turn into a red giant or Cepheid variable before puffing away its outer layers to reveal a remnant core as a white dwarf.

Ming Zhao;Monnier et al, 2007;
U. of Michigan

Larger composite image (more).

Altair's flattened ellipsoid shape
has been directly imaged (more).

Altair has one of the fastest known rotational speeds -- 210 kilometers per second (131 miles per second)-- and so completes at least one rotation in about 10.4 hours. By comparison, the rotational speed of Sol is only 25.4 days at its equator. As a result of the rapid spinning, the star probably has the shape of a flattened ellipsoid, where the equatorial diameter was estimated to be 14 percent greater than the polar diameter in 2001. Useful star catalogue numbers for Altair include: Alp or Alf Aql, 53 Aql, HR 7557, Gl 768, Hip 97649, HD 187642, BD+08 4236, SAO 125122, FK5 745, LHS 3490, LTT 15795, LFT 1499, and ADS 13009 A.

Habitable Zone

According to one type of model calculations performed for the NASA Star and Exoplanet Database, the inner edge of Altair's habitable zone is located relatively far from the star at around 2.177 AUs from the star, while the outer edge lies even farther out at around 4.475 AUs. The distance from Altair where an Earth-type planet would be "comfortable" with liquid water is centered around 3.3 AUs -- at the outer reaches of the Main Asteroid Belt's orbital distance in the Solar System. At that distance from the star, such a planet would have an orbital period of around 4.7 Earth years. If there is life on any Earth-type planet orbiting youthful Altair, it is likely to be primitive single-cell, anaerobic (non-oxygen producing) bacteria under constant bombardment by meteorites and comets as Earth was for the first billion years. Since there is unlikely to be free oxygen in the atmosphere of such a planet, it probably would not have an ozone layer (O3) although Altair puts out a lot more hard radiation (especially ultraviolet) than Sol.

Hunt for Substellar Companions
A search for faint companions using the Hubble Space Telescope from 1995 to 199 found no supporting evidence for a large Jupiter or brown dwarf sized object (Schroeder et al, 2000). On the other hand, the failure to find large substellar objects like brown dwarfs or a Jupiter- or Saturn-class planet in a "torch" orbit (closer than the Mercury to Sun distance) around Altair -- with even the highly effective radial-velocity methods of Geoff Marcy and Paul Butler -- bodes well for the possibility of Earth-type terrestrial planets around this star.

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Norm Klekoda (Dark Skies Michigan; used with permission) Altair is the bright star at left of the dark nebula. (See a2MASS Survey image of Altair from the NASA Star and Exoplanet Database.) System Summary The name Altair is derived from the Arabic for "The Flying Eagle."

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It is very hot about 13,130 F that's hotter than the earth core.

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Altair is only 16.8 light-years away from Earth, making it one of our nearest stellar neighbors. At least two features of the star Altair make it distinctive.

First, Altair rotates rapidly. This star requires only about 10 hours to spin once on its axis, in contrast to 24 hours for our Earth to spin or roughly a month for our sun. In other words, this mighty star spins on its axis more rapidly than Earth! This rapid rotation tends to flatten the star a bit, much as a pizza crust flattens as it spins. Rough estimates are that Altair's flattening is about 14 percent. The sun also is an oblate spheroid, although its flattening is difficult to measure due to the low rotation rate.

In 2007, University of Michigan astronomers combined light from four widely separated telescopes to produce the first picture (above) showing surface details on Altair. The researchers, led by John Monnier of U-M, used optical interferometry to get this image. Read more about the study here.

Second, Altair stands out because it is a weak and unusual variable star with as many as nine different rates of brightness waxings and wanings. The brightness variations are too small to measure without sensitive instruments, but likely are related to the star's high rotation rate.

By the way, if Altair were substituted for our sun, at the distance the sun is now, life on Earth would be doomed, as Altair shines with 11 times the sun's visible light. However, with a surface temperature of about 7,550 K degrees (13,130 Fahrenheit or 7,277 Celsius), Altair isn't much hotter than the sun at 5,800 K (9,980 F or 5,527 C). Higher temperatures usually reveal greater mass, at least for Main Sequence stars, and Altair is thought to be in excess of 1.7 times the mass of our sun.
How to see it
Altair is the 12th brightest star, and so it is respectably bright (apparent magnitude 0.76 or 0.77), a fact that increases your likelihood of spotting it in summer or autumn skies. What's more, Altair is flanked by two other stars, Tarazed and Alshain. When you see them, you might think of these stars as walking three abreast and arm-in-arm across the heavenly sphere.

Altair is also known as Alpha Aquilae, and it is the brightest star in the constellation Aquila the Eagle.

What's more, stargazers know Altair as part of an entirely different and much-larger - but very recognizable - pattern. Altair is the southern apex of the Summer Triangle, which is also composed of the stars Vega and Deneb.

On the first of June, Altair rises about 90 minutes after sunset, as viewed from mid-northern latitudes. By the end of September it approaches the meridian as night falls. By the end of the year, late-night observers will miss it altogether as it sets less than three hours after the sun.

Many depictions place Altair as the head or neck of an eagle with outstretched wings. The tips of the wings are formed by the Theta and Zeta stars of the constellation Aquila the Eagle, with the tail being Lambda. Once visualized, Aquila the Eagle can be seen flying eastward through the Milky Way, apparently about to devour the tiny constellation Delphinus, the Dolphin.
History and myth
The name Altair is Arabic in origin and has the same meaning as the name of the constellation Aquila in Latin; that is, they both mean simply "eagle."

In classical mythology Aquila, and by extension Altair as well, was an eagle favored by Zeus. He played a part in numerous myths, including the abduction of Ganymede in which a young boy (Ganymede) is carried off to Mount Olympus on Zeus' command to become the cupbearer to the gods. In another myth Aquila is the eagle that torments Prometheus, and is shot with a poisoned arrow by Hercules.

In India, Altair with its two flanking stars, Beta and Gamma (Tarazed and Alshain), are sometimes thought to be the celestial footprints of the god Vishnu.

Altair is separated from the similar-looking (but brighter) star Vega in the constellation Lyra by the great starlit band of the Milky Way. In Asia, this hazy band across our sky is known as the Celestial River. One story common in China, Japan and Korea is of a young herdsman (Altair) who falls in love with a celestial princess (Vega), who weaves the fabric of heaven. The princess became so enamored of the herdsman that she neglects her weaving duties. This acts enrages the princess's father, the Celestial Emperor, who decrees that the herdsman must stay away from his daughter, on the opposite side of the River. The Emperor finally listened to the princess's pleas, however, and allowed the herdsman to cross the Celestial River once per year, on the seventh day of the seventh month.

In Japan, Altair is Hikoboshi, and Vega is Orihime (or Tanabata). If it rains on the day of the festival of Tanabata, it is said to be Orihime's tears because Hikoboshi could not navigate the treacherous waters of the Celestial River.

The position of Altair is RA: 19h 50m 47.0s, dec: +08° 52′ 06″

Bottom line: Altair is the brightest star in the constellation Aquila, and one of the closest stars to our solar system.

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Altair: Bright star of the Eagle | EarthSky.org

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Altair is only 16.8 light-years from Earth, making it one of our closest stellar neighbors. At least 2 features of the star make it distinctive. For one thing, Altair needs only 10 hours to spin once on its axis, in contrast to roughly a month for our sun.

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Altair has an absolute magnitude of 2.21 making it the 12th brightest star in the sky

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Altair is the brightest star in the northern constellation and is the 12th brightest star in the sky

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Altair is about 10.6 times brighter than our sun

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It is 1.63 times bigger than our sun.

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Altair is only 1.2 billion years old.

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Altair still has about 9 billion years of life.

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The Altair star, which is 12th brightest star we can see from Earth will one day be a black dwarf. When the star runs out of there material and gases there fuel will slowly fade away. An average size star like our Sun will bloat in size after a life cycle of 10 billion years and turn into a red giant. Once it is a red giant it will blow off it's gases and collapse. The collapsed star will eventually fade and turn into a white dwarf which is the inner core of the star. After the white dwarf will cool down into a black dwarf which has no light or heat. It takes so long for a star to cool off into a black dwarf it is believed that no star has yet reached this stage. Wit the Altair star being 1.7 times the mass of the sun the process will probably take a longer time then 10 billion years. The Altair star has an apparent magnitude of 0.77, it has an absolute magnitude of 2.3, and has a b-v of 0.22.

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The Altair star, which is 12th brightest star we can see from Earth will one day be a black dwarf. When the star runs out of there material and gases there fuel will slowly fade away. An average size star like our Sun will bloat in size after a life cycle of 10 billion years and turn into a red giant.