Appropriate reference?

The star Vega (the Blue Eye for the Basques) of the constellation of Lyra (Flags for the Basques) has long been regarded as standard by astronomers. They have served to calibrate the characteristics of other stars. Vega is the fifth brightest star in the sky and has helped define the temperature and brightness scales of the stars. It is therefore the most important star behind the Sun. However, some astronomers are questioning Vega's suitability.

Apparently it rotates very slowly around its axis (every five days), astronomers have considered that the temperature of its surface is constant. Astronomer Graham Hill of the Dominion Observatory of Canadian British Columbia just confirmed what many others saw: That Vega turns very fast, exactly every eleven hours. However, as we see from the pole side, it seems to us that it rotates more slowly.

The fast turn of the Vega slightly distorts the star and thickens on the equators. Distortion also means that the poles are warmer than the equator. Therefore, it cannot be used as a temperature standard.

The variability of the temperature explains some surprising points of Vega: being higher than expected and having a temperature too low to be so bright. On the other hand, the rapid rotation does not affect the brightness and there are no problems to use the Vega as a standard of brightness.

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