Comet ISON Finder Chart 2013-11-20 6am EST

The sky is forecast to be clear tomorrow morning affording a last chance to see comet C/2012 S1 (ISON) before it disappears behind the sun. It will return a couple of weeks later, also in the pre-dawn sky.

On Nov 20th (2013) comet ISON will be low in the per-dawn sky and possibly visible about an hour or so before sunrise (7:09 EST). It’s reported to be magnitude 5, which is just bright enough to see unaided under dark skies. At 5:20 EST the sun will be 18° below the horizon which is the end of “night” and the start of astronomical twilight. At this time ISON will only be about 6° above the horizon bearing 114° (a little east of SE). So a magnitude 5 object won’t likely be visible through the thick dusty air near the horizon – even with a telescope.

Over the next 40 minutes, ISON will climb to an altitude of 12° (bearing 122°). 6:00am is the start of nautical twilight so the sky will be fairly light at that time. Only the brighter stars – those used for navigation – are usually visible to the naked eye during nautical twilight. But with binoculars or a small telescope, it might be possible to see the magnitude 5 comet.

After that, it will probably be too light out to see the comet. By sunrise at 7:09 the comet will be at altitude 21° and lost in the glare of the sun.

Time Sun ISON Mag 5
EST Alt Alt Az
5:20 -18.8° 5.6° 114°
5:30 -17.1° 7.1° 116°
5:40 -15.4° 8.7° 118°
5:50 -13.7° 10.2° 120°
6:00 -12.0° 11.7° 122°