Every moonrise is different. Last night’s Full Flower Moon rose squat and orange like you’d expect. But about 2 minutes later it ascended through a pencil-like layer of cloud. To the naked eye it looked exactly as if someone had taken a black magic marker and neatly drew a straight line across the moon’s face. No two snowflakes match, and I’d argue the same for every moonrise. Is anything really identical to anything else except at the molecular level?
Pretty as it is get ready to bid the moon farewell. It’s moving south in the sky toward its low point in Sagittarius. For mid-northern latitudes that means it rises more than an hour later each night. Tonight’s less-than-full moon returns near the end of evening twilight. By Saturday we’ll have an hour of dark skies before the next moonrise. Use that time to get reacquainted with one of the brightest stars of the late spring and summer sky — Vega.
I’ve been watching it “leave the nest” and rise ever higher in the northeastern sky over the past couple weeks. Vega is nicely placed for viewing starting around 9:30 – 10 o’clock local time. Just face to the east-northeast, hold you balled (vertical) fist at arm’s length and measure about two fists up from the horizon. The singular, bright, white star you’ll see is Vega, pronounced as either VAY-guh or VEE-guh. It’s the 5th brightest star in the sky and the head luminary of the faint but distinctive constellation Lyra the harp.
Located just 25 light years from the Earth Vega is also one of the closest bright stars. When you see it tonight the light that excites your retinal cells left the star in 1995 when the world seemed a more innocent place. Vega is similar to the sun in that it fuses hydrogen atoms in its core to create energy, but it’s hotter, more luminous (36 times as bright as our star) and 2.3 times as massive … and only 400 millions years old. 10 times younger the the sun — ah, youth!
Curiously, we view Vega pole-on. That is, it’s pole points almost directly toward the Earth. Vega spins incredibly fast — about 972,000 miles per hour (270 km/sec) or 219 times the speed of the sun at its equator. Because gases flex and flow Vega’s rapid spin has shaped it into an egg.
Four stars below Vega and one to its left form an imaginary harp, the reason why Vega is also known as the Harp Star. Once you spot Vega you can use it to locate two easy asterisms called the Lozenge and the Keystone. Asterisms are bright patterns of stars within a constellation that have a distinctive shape and are easy to find. The Lozenge belongs to Draco the dragon and the Keystone to Hercules. When learning new constellations it’s most helpful to start with a bright star, then an asterism and finally the constellation itself. We’ll explore both Hercules and Draco in the coming weeks.