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What's Up with Comet ISON: September 26 update
What's Up: Brought to you by Jane Houston Jones
Chart showing ISON's path low on the horizon at dawn near Mars.
Look for ISON near Mars at dawn.

Comet ISON was first reaquired by amateur astronomer Bruce Gary in mid-August and has been imaged by more and more eagle-eyed observers with good astrophotography equipment since then.

If you have ever tried to view a faint comet through a telescope, or tried to photograph one, you know it takes some practice. Since comets are diffuse, the brightness is spread out, so a magnitude 10 comet will appear fainter than a magnitude 10 star - which is a point of light. Luckily, you have two months to practice spotting ISON before Perihelion, and Jupiter and Mars provide easy to see "guideposts" to find Comet ISON's location.

Color image of ISON against a background of stars.
Damian Peach's view of ISON on 24 Sept. Used with permission.

The time to view comet ISON is during the hour or so before dawn. The night before your first viewing attempt, be sure you know which direction is East. For your first outing, you may just want to try from your front or back yard. Set your alarm, find East and look for bright Jupiter nearly overhead at dawn. On October 24th-26th, you'll find the moon below Jupiter high in the southern morning sky. Now try to spot Mars, 30 degrees above the horizon (or one third of the way to overhead) at the end of September and beginning of October, rising 4- 5 hours before sunrise.

You'll find the moon above Mars on September 30th and below Mars on Oct. 1. You'll need an unobstructed view to see that low to the horizon, but the good news is Mars will be rising higher in the sky between now and late November.

Here's an excellent Star Chart showing Comet ISON's path near Mars in late September and early October, courtesy of Skyhound's Skytools3 software. Concentrate on locating Mars and the Beehive Cluster first. They are naked eye or binocular objects that make great signposts to spot the comet low in the eastern sky at dawn.

How bright will the comet be in the next few weeks? To see with your unaided eye, it will need to be magnitude 5-6, binoculars, magnitude 7-8, telescopes to about mag 9-10 in the brightening dawn sky. In a darker sky, an experienced comet observer or astrophotographer will see to magnitude 12 or fainter. Right now the comet is about magnitude 11.3. So concentrate on location, location, location right now, and spot Jupiter and Mars, the pointers to comet ISON.


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About: Jane Houston Jones
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Jane is an astronomer, NASA science podcast developer, writer, educational and outreach artisan and social media enthusiast. She and her husband have an asteroid (22338 Janemojo) named after them.
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Last Updated: 27 Sep 2013