The constellation Corvus, the crow, glows to the lower right of the brilliant star Spica on May evenings. Its brightest stars form a pattern that resembles a sail. Two names are shown for each of the crow's major stars. The top name is its designation by Johann Bayer, who used letters of the Greek alphabet to label the stars in every constellation. "Alpha" usually designates a constellation's brightest star, but in this case it is applied to a relatively faint star. The bottom name is the star's proper name, which generally pre-dates the Bayer name by centuries. [background image: NASA/ESA/Z. Levay (STScI)/A. Fujii]
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You can organize a constellation’s stars in many ways — by brightness, color, position, and so on. But the system that astronomers have been using for centuries can’t quite make up its mind. In most cases, it goes by brightness. In others, it goes by position. And in some, there doesn’t seem to be a guiding principle at all.
An example of the latter is Corvus, the crow. It’s due south at nightfall, to the lower right of bright Spica, the leading light of Virgo.
Four stars form an angled box that looks like a sail. A fainter star is off the lower right point of the sail. Yet it receives top billing.
The naming system was devised more than four centuries ago by German astronomer Johann Bayer. He labeled the bright stars in each constellation with the letters of the Greek alphabet. “Alpha” usually designated the brightest star. In some instances, though, the title went to a star that was the starting point for an easily defined pattern.
In the case of Corvus, though, there doesn’t seem to be any pattern at all to Bayer’s naming system. The stars aren’t named from top to bottom, left to right, or in a circle. They don’t form any logical order within the figure of the crow, either.
And the Alpha star is only the fifth-brightest in the constellation — a faint pinpoint that’s not even visible under light-polluted skies.
So no one is quite sure what Bayer was thinking when he named the stars of this pretty little constellation.