A Guide to Viewing ISON

This blog was written by AccuWeather Astronomy on Facebook content creator Paul Adomshick.

As Comet ISON (designated C2012/S1) continues to get closer to the sun, and is slowly brightening, we at AccuWeather Astronomy have begun to get more questions about when and where to look for ISON. Right now, it is not visible to the naked eye, because it is at roughly magnitude 9 (the lower the number, the brighter the object). In the best dark sky conditions, an experienced observer with outstanding vision would be fortunate to be able to distinguish magnitude 7 objects. Right now, ISON is predicted to brighten roughly 0.1 magnitude each day, so we are still a few weeks from possibly being able to see ISON with the naked eye. For amateur astronomers with telescopes, it can be seen now, less than 5 degrees away from Mars. At arms length, the width of your palm covers roughly 10 degrees of the sky, and would be able to obscure both Mars and ISON, if ISON was visible to the naked eye.

As we continue into November, Mars will be rising early in the morning, but ISON will be moving farther and farther from Mars each day. However, Mars will be a good guide for finding ISON as it continues to brighten. Hopefully, by mid-November, ISON may be visible to the naked eye very low above the Eastern horizon, as it rises a couple hours before sunrise. On November 15 it will be located roughly 30 degrees away (three hand widths away) from the sun. ISON will continue getting closer to the sun each day, so there will only be a very brief and shrinking window of time each morning between when it rises and when the sunrise makes the sky too bright to see ISON, if it becomes visible to the naked eye at all before perihelion, its closest approach to the sun on November 28.

Because ISON is a newly discovered comet, and is believed to be making its first visit to the sun, how quickly it will brighten is very uncertain. Whether ISON will brighten enough to be seen with the naked eye before perihelion is still not known, because we cannot be sure exactly how quickly ISON is going to brighten as it approaches the sun, or what its greatest magnitude will be. There is a slight chance, if it brightens very rapidly, that it could be bright enough to be visible in the daytime in the days closest to perihelion. Because ISON is considered a “sun grazer”, a comet with an orbit that takes it very close to the sun, it may break up during its turn around the sun. That could actually be to the benefit of viewers, because if it breaks up, it could give off a very bright burst of dust and ice.

If ISON does not brighten enough before perihelion to be seen with the naked eye, it is likely that the days after perihelion, probably around the second or third week of December, will be your best opportunity to see ISON. At that time, it will still be a reasonably bright object, but will be far enough away from the sun that it will rise while the sky is still dark in the hours before sunrise each day. Additionally, because ISON does not orbit in the same plane as the planets, after perihelion, it's orbit will take it higher in the sky, allowing it to be seen for a short time, low in the northwest sky just after sunset each day.

On Christmas, ISON will rise early in the morning, and should still be visible to the naked eye, although it may require a little effort to find it. Binoculars, or the zoom lens on a tripod-mounted camera should help you in your effort to see ISON on Christmas morning. Since little ones are likely to be up by 6am with the anticipation of what Santa has brought them, if skies are clear, it might be a nice present to show them the “Christmas Comet” before the sun rises.

As we get to January 2014, ISON will be starting to get very dim, and by mid-January will no longer be visible to the naked eye.

The sources I used for this blog were Stellarium free planetarium software, the Comet ISON Interactive Model solarsystemscope.comand the ephemeris data provided by the Minor Planet Center.

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