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Friday, October 8, 2010

Comet Hartley 2

My first observation though binoculars was a few nights ago. The comet is difficult but will be easier to see as the month progresses.

Comet Hartley 2 is said to be large and diffuse, meaning its light is spread out over a wide area. You will definitely need a dark, country sky - free of city lights - (well, Harare has very few street lights and constant power-cuts, so your chances are good!) to see it. Also, when searching for the comet, remember to use averted vision. That's the technique of looking to one side of the faint object you seek on the sky's dome, instead of directly at it. This comet might become faintly visible to the unaided eye in October 2010. Only time will tell if this will happen.

To find the comet, first find the constellation Cassiopeia the Queen. This constellation is easy to spot in the northeast in the evening now. Cassiopeia is shaped like the letter M or W. This comet will sweep next to Cassiopeia in late September and early October 2010.

Just remember . Cassiopeia always appears in the northeastern sky at nightfall on October evenings. It swings low in the northern sky - above Polaris, the North Star - in the wee hours after midnight in October. Then, as night progresses toward dawn, you'll find Cassiopeia in the northwestern sky before dawn. Just look in the locations mentioned above for a W or M-shaped star pattern.

What will the comet look like?

Comets are surprising objects in many ways. They are mysterious visitors - loosely bound balls of ices - from the outer solar system. Sometimes, comets appear without warning. Comet Hartley 2 has been expected for many years, however. Officially designated 103P/Hartley, it is a periodic comet, which returns again and again near our sun and Earth. Its orbital period is thought to be 6.46 years.

Even so, the brightness and appearance of this comet - or any comet - never follows an ironclad forecast. Don't be surprised if Comet Hartley 2 exceeds or falls shy of expectation. Through your binoculars in October, it should look like a smudge of light against the dark sky background. Comet Hartley 2 may look like a faint, fuzzy star. Or it might exhibit a discernible tail. We'll have to wait and see.

The element of suspense always accompanies the return of a comet to Earth's sky. That's one reason they are fun to see!

How to find Comet Hartley 2 with binoculars

A typical binocular field covers about 5 degrees of sky. Sometimes the field of view (F.O.V.) is listed right on your binoculars. For handy reference, the distance between the Cassiopeia stars Caph and Schedar measures about 5 degrees. Remember this, as it will serve you well on your hunt for Comet Hartley 2.

After October 10, finding the comet gets tricky, because the moon will be returning to the evening sky. The moon's glare will make the comet harder to see. It will probably be best to observe Comet Hartley 2 after moonset from October 11 to October 20.

By the way, the Deep Impact spacecraft - which was launched by NASA in 2005 and successfully sent a collider into Comet 9P/Tempel - had its orbit around the sun tweaked in May of 2010 with the goal of sending it close to Comet Hartley 2. This mission has now been re-designated EPOXI. The craft will pass most closely to the comet in early November, 2010. Mission overseers are provided status updates for EPOXI's impending sweep past Hartley 2.

All in all, it will be an interesting autumn season for comets, thanks to Comet Hartley 2. Be sure to make friends with Cassiopeia, your tour guide to the comet. The trick to comet hunting is to know right where to look for its place in the starry sky, and Cassiopeia will help. Comet Hartley 2 has now been spotted under dark skies by people using binoculars, and it might reach naked-eye visibility in October.
Mike Begbie


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