If you were to gaze at the night sky for a considerable amount of time during the summer months in the northern hemisphere, you would likely come across a constellation triangle, aptly named the Summer Triangle. At the apex of this triangle, you may identify the twelfth brightest star in the night sky: Altair. While you may be mesmerized by the brilliance of Altair, this white sequence dwarf star, located 16.7 light years away, it is actually a weak and unusual star for its type.
Its name, derived from the Arabic phrase, “the flying eagle,” effectively addresses the star’s remarkable rotational speed, which can reach 210 kilometres per second. Unlike our beloved sun, which spends 25.4 days rotating around its axis, Altair completes one rotation in a mere 10.4 hours.
Altair’s great speed accounts not only for the flattening of its poles, giving the star its distinguishable ellipsoidal shape, but it also affects the star’s brightness — creating as many as nine rates of luminosity with sequential waxing and waning. What’s more, unlike our sun, whose rotational speed only characterizes it as an oblate spheroid, Altair’s rapid rotation decreases both its temperature and its surface gravity at the equator, making the poles more luminous than its equator. This abnormality is called the von Zeipel effect, or gravity darkening.
Altair’s abnormality can also be attributed to its unusual brightness for its spectral type and size. While the star is only a few hundred million years old, its large diameter and high temperature account for its quick exhaustion of hydrogen. Scientists estimate that its outer layers will exhaust in a mere one billion years, to reveal a white dwarf.
As with every observable star, much research has been performed to locate planetary bodies in the star’s vicinity. Scientists have hypothesized that Earth-like planets may reside in its distant orbit. Due to Altair’s higher radiation production, the orbit of a terrestrial planet would be about four times that of our beloved blue planet. Similar to Earth’s development during the sun’s early years, a terrestrial planet orbiting young Altair would consist of life in its primitive anaerobic cell stage. Their hypothesised anaerobic development is due to the presumed lack of free-roaming oxygen in the atmosphere, which would also contribute to a lack of a properly established ozone layer. This would not only lead to the planet’s constant bombardment by comets, asteroids, and meteorites, but also to experiencing greater amounts of ultraviolet radiation on its surface.
Since Altair has always been readily visible in the night sky, and is part of a commonly recognized constellation, it is difficult for academics to agree on the specific date and event of its discovery. However, it is known that the star was under regular observation prior to 1918, when Capitan Piper observed seven meteors shooting below Altair.
In addition to being one of the closest stars to our own, Altair is also know for being the first small, hydrogen-burning star that astronomers have been able to photograph. While recent developments have created a few red giant images, tiny stars usually appear as points of light even on the largest telescopes. The pictures were taken in June of 2007, using four telescopes that are able to modify Earth’s atmospheric distortions.
Although Altair is visible with the naked eye, next week we will assay one of NASA’s airborne observatories, which marked its 35th anniversary earlier this year. Until then, marvelous space stories await your discovery.
