Slipping Toward Vega

By Bob Berman|Saturday, July 01, 1995
RELATED TAGS: STARS

Away from city lights, a moonless July sky displays about 2,500 naked-eye stars. With so many luminaries, how hard is it to select one standout to feature on this page? It’s a piece of cake. Most stars are dim, and most are cursed with monikers like HDE224334 or Zubeneschamali. Only a handful are brilliant and have popular names. Of those, just one floats overhead during the summer. So it’s automatic: Vega selects itself.

From most of the Northern Hemisphere, it appears as the third brightest star in the sky, and it boasts the shortest and one of the most familiar names. (Nonetheless, its name is mispronounced routinely. That’s because few know this phonetics tip: star names should be pronounced as they’re spelled.

Rigel is really RYE-gel and Vega is really VEE-guh. No need to add a Latin twist with VAY-guh and make it into a cigar.)

Look straight up at midnight and there it is, its blue white contrasting perfectly with that other near-zenith denizen, orange Arcturus. But the latter never sits straight up. For most Americans, those living between latitudes 36 and 44, Vega is unique: it’s the only bright star that ascends to within a few degrees of the exact zenith.

Shining at a steady magnitude zero, Vega serves as the standard candle used by the worldwide astronomical community to calibrate the brightness of everything else in the universe. In astronomical jargon, magnitudes greater than zero are progressively dimmer; negative magnitudes are increasingly brighter. The sun, for example, is magnitude -26.8. Like the French bar of platinum that defines the meter, Vega is the sky’s reference point for the magnitude system. It’s an ideal choice because it displays not the slightest flickering or unsteadiness. Its brilliance, equal to 58 suns, emanates from a dazzling 2.7-million-mile-wide ball whose surface is nearly pure hydrogen. Vega floats relatively close to Earth-- it’s just 26.5 light-years away.

But it’s still not quite a monument to normality. A year ago a team of Canadian astronomers announced that Vega, like a bigamous bank teller, has unsuspected peculiarities. It spins much faster than anyone imagined, one rotation in a giddy 11 hours (compared with 25 days for our sun), and its pole of rotation is pointed straight toward us, give or take five degrees. This means that any Vegans looking skyward would see our sun as their north star!

Twelve thousand years from now, we’ll return the favor. Vega periodically becomes our polestar as Earth’s axis wobbles through its 26- millennium precession. Brightest of all north stars, it nonetheless misses the celestial pole by nearly five degrees, making it ten times less precise than the current one, Polaris.

As if there weren’t enough to keep us interested, Vega marks the approximate direction toward which we travel in space. As our entire starry neighborhood participates in the galaxy’s grand rotation, we do a little 12-mile-per-second sideslip in Vega’s direction. Those who think that the whole universe races away from us are mistaken. In a cosmos where the redshift is as common as ham and Swiss, this diamond at the zenith displays the much rarer blueshift.

So enjoy the pastel tournament above as the two brightest summer stars branch off in different directions. While Arcturus will vanish from sight in a half-million years, Vega will only grow brighter as it heads our way, keeping our descendants company through the eons.

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