Vega

Vega is Alpha Lyrae, apparent magnitude 0.03, at 25 light years, spectral type A0Va. It is the fifth-brightest star in the sky and the second-brightest in the northern celestial hemisphere.

Its importance to astronomy is largely technical. Vega was for a long time the zero point of the magnitude scale, the star against which brightnesses were defined, so that its magnitude was zero by convention. It served the same role for colour indices. Modern systems have moved on, but Vega-relative magnitudes are still in use and the star remains one of the most heavily observed calibration objects in the sky. It was also the first star other than the Sun to be photographed, at Harvard in 1850.

Two physical facts complicate the calibration. Vega rotates extremely rapidly and is seen nearly pole-on, which means it is substantially oblate and its apparent surface is hotter and brighter than its equator, the star we measure is not the star an equatorial observer would measure. And it has an infrared excess, discovered by the IRAS satellite in 1983, indicating a surrounding disc of dust. Vega was the first star found to have such a debris disc, and the discovery opened the study of planetary system formation around other stars. It is the archetype of what are still called Vega-like stars.

The name is from Arabic, from a phrase meaning the swooping or falling eagle or vulture.

Vega forms one corner of the Summer Triangle with Deneb and Altair. The three are strikingly unequal: Vega is nearby and modest, Altair nearer still, and Deneb lies at something like 2,600 light years and is one of the most luminous stars known, appearing comparable only because it is so far away. The triangle demonstrates neatly that apparent brightness says nothing about a star until its distance is known.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy

Vega is the best illustration in the sky of the scale of precession, because it has held and will hold the position that Polaris holds now.

The earth's rotational axis traces a circle on the sky with a period of about 25,800 years. Vega lies close to that circle. It was the pole star around 12,000 BC, roughly fourteen thousand years ago, and it will be again around the year 13,700. Between those dates the pole moves through Thuban in Draco, which was the pole star of the Egyptian pyramid builders around 2700 BC, and then to Polaris.

This should be set against the astrological reading of the star, and the point is that it does not belong to it at all. Vega's traditional nature is Venus and Mercury, giving refinement, artistic and musical gifts, idealism and a certain loftiness. Nothing in that reading references the pole, because at no point in the history of Western astrology has Vega been near it. The precessional fact is real and is simply irrelevant to the tradition, which is worth saying plainly, because modern writing about fixed stars has a tendency to import any impressive astronomical fact it can find and attach significance to it retrospectively.

Ptolemy gives Vega a Venus and Mercury nature, and the constellation reinforces it: Lyra is the lyre of Orpheus, and a star in a musical instrument acquires a musical character. The lyre association is at least as old as the Greek constellation figure and probably older.

Agrippa pairs Vega with chrysolite and winter savory in the Behenian list. Chrysolite is an unstable name that has meant peridot and chrysoberyl at different periods, so the intended stone is not certain.