By Bruce McClure
If you have binoculars, start searching for Comet Garradd in November 2011. This post tells you how to find the comet in front of the constellation Hercules.
Comet Garradd and the Coathanger in early September 2011
Feel like chasing a comet? Grab your binoculars and head for a clear dark sky to see Comet C/2009 P1 Garradd. It’s the sky’s most conspicuous comet now, approaching sixth-magnitude in brightness. It’s visible through binoculars, even though the comet is quite faint. The last time I looked, Comet Garradd looked like a ghost of a fuzzball in my 10×50 binoculars, with no hint of a tail. All the same, it’s a great thrill to catch this creature of the wild roaming in the wilderness of the solar system.
This comet is predicted to remain at about the same brightness until March 2012. The magnitude isn’t expected to change greatly over the next several months, though Comet Garradd will probably peak in brightness in February 2012.
And there’s more good news. Until now, Comet Garradd has been traveling relatively rapidly across our sky, passing many constellations along the way, making it a hard target to track for casual viewers. Now, though, the comet has settled into a region of the sky near a noticeable star pattern, or asterism – the famous Keystone asterism of the constellation Hercules. Comet Garradd will be in front of Hercules from now until February 2012. So finding Hercules – and its Keystone star pattern – is your ticket to seeing Comet Garradd.
Ready? Let’s chase a comet!
How to find the Keystone in Hercules
At mid-northern latitudes throughout November, the constellation Hercules and its Keystone asterism appear in the western sky at nightfall. Hercules falls downward throughout the evening hours and sinks behind the northwestern horizon by around mid-evening. So find an unobstructed western horizon, and do your comet-hunting at nightfall and early evening.
Vega is your guide star to the constellation Hercules.
To locate Hercules and the Keystone, you need to know two reference stars. One is noticeable for being part of a large triangular pattern in the sky – The Summer Triangle – which is much bigger than the Keystone! The other star is noticeable because … well, it’s just in a noticeable spot now, low in the west at nightfall. The two guide stars shine on opposite sides of the Keystone, so look for the Keystone between these stars. They are Vega and Gemma (otherwise known as Alphecca).
The bright star Vega pops out quite high in the western sky at dusk and nightfall. Many are familiar with Vega because it’s the brightest star of the Summer Triangle asterism. The first-magnitude star Vega serves as your premier signpost to Comet Garradd.
Vega is your guide star to the constellation Hercules.
The second-magnitude star Gemma (Alphecca), the brightest in the C-shaped constellation Corona Borealis, lurks low in the west to northwest sky at nightfall and early evening. If it’s dark enough, you’ll easily recognize Gemma (Alphecca) as the brightest star in the graceful semi-circle of stars known as Corona Borealis.
The Keystone of Hercules is found by using the two guide stars, Vega and Gemma (Alphecca). On a dark night, the Keystone sticks out like a sore thumb roughly midway between Vega and Gemma. It’s a squarish pattern, with four modestly bright stars marking the corners of the square. Remember, the Keystone is famous! You can see it, if you let your eyes look for patterns among the stars. As evening deepens into late night, Gemma sets first at early evening, the Keystone sets an hour or two thereafter, and Vega sets last around midnight.
Look left of the Keystone asterism in the constellation Hercules for the guide stars Rasalhague and Rasalgethi and Comet Garradd.
Once you know the Keystone, try to branch out from there to fill out the stick figure of Hercules. A good familiarity with Hercules will enable you to star-hop to Comet Garradd.
Rasalhague, second-magnitude reference star
As shown on the above sky chart, look about 20 degrees to the left of the Keystone to find the second-magnitude star Rasalhague. Your fist at arm’s length spans about 10 degrees of sky, so look for this star about two fist-widths to the left of the Keystone. It’s the brightest star in this realm of sky, not far from the somewhat fainter star Rasalgethi in Hercules.
Omicron Herculis, the fourth-magnitude star to the upper left of the Keystone and the lower left of Vega, is rather faint but easily visible to the unaided eye on a dark night. You can find Omicron Herculis pretty much in line with Vega and Rasalhague. If you can see this star with the naked eye, that’s a good sign, as it’s more likely that you’ll also catch Comet Garradd with binoculars.
Throughout November 2011, Comet Garradd is found between the star Omicron Herculis on one side and Rasalhague and Rasalgethi on the other. Search for this comet about one-third of the way from Rasalhague (or Rasalgethi) to Omicron Herculis. Click on the image to the lower right for a more detailed sky chart showing the path of Comet Garradd in front of Hercules.
Star-hopping with binoculars to find the comet
Before looking for any comet, it’s best to practice star-hopping to deep-sky objects with binoculars. Since you’ll probably be using the Keystone to star-hop to Comet Garradd, how about star-hopping to the Hercules globular star cluster (Messier 13) right off the bat? Through binoculars, the Hercules cluster looks like a dim and possibly fuzzy star. With a good telescope, you can begin to appreciate the Hercules cluster for what it really is – a globe-shaped stellar city teeming with hundreds of thousands of stars.
To see an enlarged PDF version of this chart, click here.
The Hercules cluster (Messier 13) is only somewhat brighter than sixth magnitude, which means it’s just barely bright enough to perceive with the unaided eye. You need a clear, dark night and eagle-eyed vision to see this sixth-magnitude object as a faint speck of light. More than likely, you’ll need binoculars to spot the Hercules cluster.
It’ll be good practice to observe this cluster with binoculars time and time again before searching for a comet that may or may not reach sixth magnitude in brightness. Once you’ve become accustomed to finding the Hercules cluster (Messier 13), try finding Hercules’ fainter globular star cluster, Messier 92. At 6.5 magnitude (the higher the magnitude, the dimmer the object) Messier 92 is somewhere around 1.5 to 2 times dimmer than Messier 13.
Comet Garradd will pair up with Messier 92 on February 3, 2012. So think photo opportunity! If you’re able to locate Messier 92, you can then use this star cluster to find Comet Garradd.
Sky chart of the constellation Hercules, including M13 and M92
Use the bright star Vega to find the Keystone of Hercules, and then use the Keystone to locate M13, the great Hercules cluster.
Sky chart: Wikimedia Commons
Tracking down and spotting Comet Garradd with binoculars won’t come easily. I first saw it as a small, faint fuzzball in my 10×50 binoculars on the evening of October 23.
You’ll need a good familiarity with the constellation Hercules and a detailed sky chart to find this comet. (Click here for another sky chart.) Plus, you’ll need a dark, moonless night and perhaps 10 to 20 minutes in the dark to give your eyes time to adapt. EarthSky reader Willow Lepanto sums it up most eloquently: “love chasing something untouchable … and uncatchable.”
But if you’re up for the challenge, Comet Garradd may be yours to behold on dark, moonless nights in the autumn of 2011 and winter of 2012!
via How to see Comet Garradd in November 2011 | Astronomy Essentials | EarthSky.