If you were out meteor-watching the past week and happened to be flat on your back looking straight up you probably saw a brilliant, white star. That was Vega, the brightest luminary in the constellation Lyra the Harp and the fifth-brightest sun in the night sky. Vega shines almost directly overhead around 10 p.m. local daylight time in mid-August.
If you live on the 39th parallel north Vega passes directly through the overhead point called the zenith. Cities at or close to that latitude include Washington D.C., Cincinnati, St. Louis, Topeka, Colorado Springs and Sacramento. North of that line Vega slides somewhat south of the zenith. And if you live south of 39° latitude it inches into the northern sky.
But no matter where you live in North America, if it's 10 o'clock you'll need to twist your neck a little to see Vega. Or lie down in the grass with your hands tucked behind your head. Much better.
Astronomers use the magnitude scale to assign a celestial object's brightness. Counterintuitively, the brightest objects have negative magnitudes. The sun scores a -27; the full moon -13; Venus -4.9; Jupiter -2.9; Sirius -1.5; Betelgeuse 0.6 and the North Star glows at 2.0. The faintest star typically visible from a rural sky is magnitude 6.0,, and the Hubble Space Telescope can dig down to 31.5. The new James Webb Space Telescope, targeted for launch on October 31, will see stars as faint as magnitude 34.
Vega gleams at a nifty 0.0, just a few tenths of a magnitude behind Arcturus, making it the summer sky's second brightest star. Two things factor into its radiance. First, Vega is close to us, just 25 light-years away. Second, the star is 2.3 times as massive as the sun and 36 times more luminous. Based on its temperature and composition, astronomers estimate Vega's age at around 400 million years, more than 10 times younger than the sun. When the star first winked into existence, the first insects and four-legged animals were evolving on Earth.
Oddly enough, we look straight down at Vega's pole from our vantage point on Earth rather than across its equator. Young stars often spin rapidly, and Vega is no exception. Its rotation rate of 972,000 miles an hour is 219 times faster than our sun. Where our star takes about 27 days to go around once, Vega whips around in just 16 hours. Because gaseous objects like stars flex as they spin, Vega's speedy rotation has stretched it into a shape resembling an egg.
During photography's early days in the mid-19th century, astronomers were eager to record the first images of celestial objects using the daguerreotype process, a messy business involving metal plates, light-sensitive chemicals and processing the images with mercury vapor fumes. The first astronomical photograph was of the moon in 1840, but the first star other than the sun to pose for the camera was Vega on July 17, 1850. Astronomer William Bond and photographer John Adams Whipple made a daguerreotype of Vega at the Harvard College Observatory using a 15-inch (38-cm) refractor.
Vega may host a Neptune-sized planet that closely orbits the star every 2.4 days. Seared by Vegan heat, the object's surface broils at around 4,500° F. While that discovery is still tentative, we do know that Vega sits at the center of a dusty disk that extends at least 330 times Earth's distance from the sun around the star. Denser blobs of dust within the disk could indicate the presence of additional planets still enveloped in cloudy debris from their formation.
You're familiar with Earth's rotation on its axis and revolution around the sun, but our planet also wobbles a bit. Gravitational forces exerted by the sun and moon on Earth's equatorial bulge (the planet's a bit bigger around at the equator compared to the poles), causes the axis to slowly gyrate with a period of around 26,000 years. Right now the north end of the axis points at Polaris in the Little Dipper, our current North Star. But in about 12,000 years it will instead point toward Lyra, and Vega will become the North Star.
On that late date you'll have to travel to the vicinity of the North Pole to see Vega overhead. Yet another reason to go out and see it tonight in A.D. 2021. Clear skies!
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.