Vega (Alpha Lyrae) is a beautiful bluish-white star located 25 light-years away in the constellation of Lyra. In addition to being the fifth brightest star in the night sky, it has other claims to fame, not least of which is it being the first star other than the Sun to have its picture taken, the very first star to have its spectrum recorded, and among the first stars to have its distance from Earth calculated by parallax. Furthermore, Vega was also once the Pole Star, and it will be again in about the year 13,727, when its declination will be +86°14′.
• Constellation: Lyra
• Coordinates: RA 18h 36m 56.33635s|Dec +38° 47′ 01.2802″
• Distance to Earth: 25.04 light years
• Star Type: Blue/White Main Sequence (A0Va)
• Mass: 2.135 solar masses
• Radius: 1.961 million km (2.362 solar radii)
• Apparent Magnitude: +0.03
• Luminosity: 40.12 solar luminosities
• Surface Temperature: 10,060 K
• Rotational Velocity: 20.48 km/s
• Age: 455 million years
• Other Designations: Wega, Lucida Lyrae, Alpha Lyrae, a Lyrae, 3 Lyr,
In both ancient Egypt and India, the constellation Lyra was represented as either an eagle or a vulture, and it is from these cultures that Vega appeared in the western world under its Arabic name “an-nasr al-waqi” meaning “the swooping eagle”. The first mention of Vega in an official Western star catalogue was in the Alfonsine Tables of 1215, and in medieval England and Western Europe, Vega was known as either Wega or Alvaca.
Vega is a blue-white (A0V) main sequence star, only halfway through its one billion year lifetime, and still in the process of fusing hydrogen into helium. It is about 40 times more luminous than our sun as it is using up its hydrogen fuel about ten times faster. Vega is also about 2.1 times more massive than our sun, but only 0.54% of its total mass consists of elements heavier than helium, making it a weak Lambda Boötis-type star.
Vega is part of an asterism of stars called the Summer Triangle, which consists of Vega in the constellation Lyra, Altair in Aquila, and Deneb in Cygnus. However, Vega can only be seen at latitudes north of +51° N, where the constellation never sets below the horizon, and remains a circumpolar star throughout the year. Look for Vega as the star at the right-angled corner of the Summer Triangle around the first of July when it culminates as it crosses the meridian.
Vegas is rotating at 236.2 km/sec at its equator, making it a very fast rotator indeed. This value translates into one rotation once every 12.5 hours, which represents 87.6% of the velocity it would take for the star to fly apart as the result of excessive centrifugal forces. Such fast rotation means that the star’s equatorial radius is 19% bigger than its polar radius, producing a pronounced equatorial bulge. Current measurements put the star’s equatorial radius at 2.818 solar radii, and its polar radius at only 2.362 solar radii. Interestingly, the unexpected high luminosity of Vegas (40 times solar) is explained by the effects of the high differential rotation on its magnetic field, which produces the higher luminosity of the polar region.
Castor Moving Group Origins
Vega appears to belong to a stellar association known as the Castor Moving Group, along with other major stars like Alpha Librae, Alpha Cephei, Castor, Fomalhaut, and about a dozen or so others. It is assumed that since the members of the group are all moving in roughly the same direction, and at about the same speed, (16.5 km/sec), all the members have a common origin in an open cluster that has become gravitationally unbound. However, there is some doubt about this because Vega is significantly older than the other stars in the group, which are estimated to be only about between 100 million and 300 million years old, making them all very much younger than Vega. Moreover, the scarcity of heavy elements in Vega implies that it was formed from material that was relatively metal-poor, but its origin remains uncertain.