Summer’s best and brightest nighttime asterism sails high over our heads as August opens. The Summer Triangle and the magnificent stretch of Milky Way it contains command the southeastern sky at nightfall. Altair in the constellation Aquila the Eagle forms the triangle’s bottom apex. For observers at mid-northern latitudes, it’s at eye level as you face to the south-southeast. Three fists held at arm’s length above Altair lies Vega in Lyra the Harp. At 10:30 p.m. local time, this prominent white star is nearly overhead.
Vega is the sky’s 5th brightest star, right behind Arcturus, which flashes like a ruby in the western sky. The eastern apex of the Summer Triangle belongs to Deneb in the constellation Cygnus, also near the top of the sky about two fists across from Vega. Once you’re familiar with these three summer sparklers, you can use them as familiar landmarks to navigate to other stars and constellations.
We’ll use the Summer Triangle to help us find Comet Garradd, the brightest comet currently visible in the sky. Don’t fret if you don’t have a telescope. You can already see this fuzzball in 7×50 or 10×50 binoculars if you’re observing from a dark site with minimal light pollution. I saw it two nights ago in my 10x50s just above the star Enif near the Great Square of Pegasus. OK, it was only a blob but it gave me a kick just the same.
But wait, there’s more!
The comet will pass very close to the bright globular cluster M15 Monday and Tuesday nights August 1 and 2. That means you’ll see two side by side blobs. Does life get any better? Telescope users will have the best view when the comet and its fat, short tail make a striking contrast with the rich star cluster. I suspect astrophotographers will burn through more than a few gigs of memory recording the event. Try to catch it this week before a bright moon returns to the evening sky.
Comet Garradd is 8th magnitude with a head or coma about 1/4 the size of the full moon (~8 arc minutes). Its tail extends better than half a full-moon-diameter from the head to the south. In a telescope, the bright nuclear or central region looks like a star at low magnification. Binoculars squeeze tail and head together into a small, blurry glow.
The comet keeps getting higher and brighter through the remainder of summer as it slices through the Summer Triangle north of Altair. By September, it will drop lower in the west but remain visible in the evening sky until year’s end for observers at mid-northern latitudes. In early 2012, Garradd moves into the morning sky, brightening all the while. While closest approach to the sun (perihelion) occurs on December 24, closest approach to Earth happens next March 5, when Garradd will be 117.7 million miles away. Then the comet will be ideally positioned in the Little Dipper, shining around 6th magnitude and faintly visible with the naked eye to sky watchers at dark sky sites.
As long as we’re on comets, the most recent observations of Comet Elenin from July 30 put it at magnitude 9.5 – 10. Nice to see it’s still climbing in brightness. If you’re out looking for Comet Garradd, keep an eye on the northern sky tonight and tomorrow night. That’s when space weather forecasters are predicting a stream of particles from a large gash in the sun’s atmosphere called a coronal hole to strike Earth’s protective magnetic bubble. Possible modest auroras might be visible at higher latitudes. Look for a greenish glow or spear-like rays just above the northern horizon. Generally, the closer to midnight – 1 a.m. you’re out, the better chance of seeing northern lights.
Those big sunspot groups are still busy and very obvious. I saw all three with the naked eye using a safe solar filter earlier this morning. Group 1263, which has the largest spots, was the easiest to see. Compare this photo to their appearances just two days ago.