Vegas (star)

Vega's position inside the Lyra constellation.

Vega (Alpha Lyrae / Allyr) is a star of the first magnitude (in Ptolemy's classification) of the constellation of Lyra and the main one of it. It is the fifth brightest star in the night sky and the third in the northern celestial hemisphere after Arthur, and Sirius the brightest. It is considered a relatively close star, only 25 light years from Earth, being one of the brightest close to the solar system. Vega has been widely studied by astronomers, coming to be ranked as the most important star in the sky after the Sun. Vega was the North Star around 12,000 BC. C. and it will be so again around the year 13720 d. C. when the declination is +86°14'. Vega was the first star, after the Sun, to be photographed and the first to have a spectral record made.

This star is only one tenth the age of the Sun, but being 2.1 times as massive its life cycle is also one tenth that of the Sun; both stars, at present, are very close to reaching the intermediate point in their life cycles. Vega is unusually poor in elements with atomic numbers higher than helium. Vega is a putative variable star that varies slightly in magnitude on a periodic basis. It rotates rapidly with a speed of 274 km/s at the equator. This causes an external bulge at the equator caused by the effects of centrifugal acceleration and, as a result, there is a temperature variation over the star's photosphere, reaching its maximum value at the poles. From Earth, Vega is observed from the direction of one of its poles.

History of your observation

On the night of 16-17 July 1850, Whipple and Bond made the first daguerrotype of a star (Vega).

Astrophotography, the photography of celestial objects, began in 1840 when John William Draper took an image of the Moon using the daguerreotype process. On July 17, 1850, Vega became the first star (after the Sun) to be photographed by William Bond and John Adams Whiple at the Harvard College Observatory, also using a daguerreotype. Henry Draper took the first photograph of the stellar spectrum in August 1872 while photographing Vega, thus becoming the first person to show absorption lines in a star's spectrum. Similar lines have been identified in the spectrum of the Sun. Professional astronomers have used Vega to set absolute standards of photometric brightness, which assumes that Vega's visual magnitude is approximately zero at all wavelengths. The original intention was for the value to be exactly zero, but in practice this was not the case. For example, in Johnson's V filter (the most widely used by astronomers in the visible range), the magnitude of Vega is 0.026 ± 0.008, and in other filters there are also deviations of a few hundredths.

Visibility

The Stival Triangle

Vega can often be seen near the zenith in mid-northern latitudes on summer nights in the northern hemisphere. It can be seen over the northern horizon during winter in mid-latitudes of the southern hemisphere. Since Vega has a declination of +38.78°..., it can only be seen in latitudes north of 51°S. This star is not visible from Antarctica or from the southernmost regions of South America, including Punta Arenas, Chile (53° S). At latitudes of +51° N, Vega remains continuously above the horizon as a circumpolar star.

This star remains as a vertex of the so-called Summer Triangle, also constituted by Altair in the constellation Águila and Deneb in the constellation of Cygnus. The Summer Triangle is very recognizable in the northern skies since few bright stars exist in its vicinity.

The Lyrids are a strong meteor shower that peaks on April 21-22. When a small meteor enters Earth's atmosphere at high speed, it produces a trail of light as the object is vaporized. During a shower, a large number of meteors arrive from the same direction, and from the observer's perspective, the bright trails appear to be radiating from a single point in space. In the case of the lyrids, these meteors are irradiated from the constellation of Lyra. However, these are currently known to be debris emitted by comet C/1861 G1 Thatcher and have nothing to do with the star.

Physical properties

Vega's spectral class is A0V, making it a white main sequence star with bluish hues, which is fusing hydrogen and forming helium at its core. The current age of the star is around 455 million years. Vega will become, in the future of its life cycle, an M-class red giant and will lose much of its mass, eventually becoming a white dwarf. At present, Vega is more than twice the mass of the Sun and its luminosity is about 37 times that of the Sun. However, due to its high rate of rotation, the pole is considerably brighter than the Ecuador. When observed from Earth, its brightness rises to 57 the luminosity of the Sun, since it is observed from one of its poles. Most of the energy produced in the Vega core is produced by the carbon-nitrogen-oxygen cycle (CNO cycle). This is a nuclear fusion process that requires temperatures of around 15 million K, which is much higher than the temperature in the Sun's core, but is much more efficient than the Sun's fusion reaction.

Vega has a disk of dust and gas around it that was discovered by the IRAS satellite in the mid-1980s. This may mean that it either has planets, or that they could form relatively soon. It also has a relatively flat spectrum in the visual region (a range of wavelengths from 350 to 850 nanometers, most of which are visible to the human eye), so the flux densities are approximately equal, 2000-4000 Jy. The Vega flux density decreases rapidly in the infrared and approaches 100 Jy in 5 micrometers.

Rotation

When Vega's radius was measured with great precision with an interferometer, it yielded an unexpected estimate of 2.73 ± 0.01 times the radius of the Sun. This is 60% larger than the radius of the star Sirius, while the stellar models indicated that it should only be 12% larger. However, this discrepancy can be explained if Vega is a rapidly rotating star that is viewed from the direction of its rotational poles. Observations made in 2005-06 confirmed this deduction.

Comparison of size Vega (left) with the Sun (right)

Vega is an example of a rapidly rotating star, such as Altair (α Aquilae) or Regulus (α Leonis), so its equatorial radius is significantly larger than its polar radius. A high rotation speed also generates surface temperature differences between the equator and the poles. The rotation speed at Vega's equator is 275 km/s, making the poles at a surface temperature of 10,150 K and the equator at a temperature of 7,900 K.

Etymology and cultural significance

The name Vega comes from a transliteration of the Arabic word wāqi‘ (واقع) which means “falling” or “landing”. The term “Al Nesr al Waki” (lowing eagle) appeared in the star catalog of Al Achsasi Al Mouakket. The Arabic name later appeared in the Western world in the Tablas Alfonsíes, which were drawn between 1215 and 1270 by order of Alfonso X.

In the present, the North Star is Polaris, but around 12,000 B.C. C. the polar star was Vega (only five degrees from it). Due to precession, Pole Star will be close to Vega around AD 14,000. C. Vega is the brightest of all successive Pole stars. Among the inhabitants of northern Polynesia, Vega was known as whetu or te tau, the star of the year. During a historical period, this star marked the beginning of a new year, when the soil had to be prepared for planting. With the passage of time, this function passed to the Pleiades.

The Assyrians named this pole star Dayan-same, the “Judgment of Heaven”, while by the Akkadians it was named Tir-anna, “Life of the Heavens". In Babylonian astronomy, Vega must have been one of the stars called Dilgan, “Messenger of Light”. For the ancient Greeks, the constellation of Lyra was formed by the harp of Orpheus, with Vega as its handle. In Chinese mythology, there is the love story of Qi Xi (七夕) in which Niu Lang (牛郎, Altair) and her two sons (β Aquilae and γ Aquilae) are separated from their mother Zhi Nü (織女, Vega). who is located on the far side of the river, the Milky Way. However, once a year on the seventh day of the seventh month of the Chinese lunisolar calendar, a bridge is made so that Niu Lang and Zhi Nü can be together again for a short time. The Japanese festival Tanabata, in which Vega is known as orihime (織姫), is based on this legend. In Zoroastrianism, Vega is sometimes associated with Vanant, a minor divinity whose name means “conqueror”.