UPDATE: Comet ISON, a "shining green candle in the solar wind," is no longer with us, NASA declared Monday morning December 3 in a tribute to what many hoped would be "the comet of the century."
We continue our coverage from last month’s installment of what’s being heralded as the "Comet of the Century." Here’s what you can hopefully expect to see during this month:
About 30 minutes before sunrise on the morning of December 1st, look above the east-southeastern horizon for Comet ISON. You will likely see a long curving tail sprouting from its head or nucleus (or what’s left of it after grazing the Sun—see last month’s installment). It should be quite obvious to the unaided eye and a splendid sight in binoculars. When the comet was approaching the Sun last month its tail trailed the nucleus, being spawned by radiation pressure from our Daytime Star. But now that the comet has rounded the Sun and is heading away from it back out into space, it’s going tail-first!
Each succeeding morning, the comet rises higher in the sky and the tail grows longer. The nucleus (or what’s left of it!) itself fades back to 2nd or 3rd magnitude from its brief daytime rise to glory. If predictions hold up, the comet should continue to be a striking sight to the unaided eye well into the month and truly wondrous in binoculars. The tail itself is expected to continue to grow in apparent size and may span as much as 10 or 15 degrees by mid-month—that’s 20 to 30 full-Moon diameters! Some forecasters are even saying that it could span a quarter of the way around the sky!
It should be mentioned that telescopes should give fascinating views of the head of the comet (which actually consists of the nucleus itself and a nebulous area around it called the coma) and inner part of the tail. But even at low power, such scopes typically can’t begin to encompass the entire object with their limited fields of view compared with binoculars. An exception is the Edmund Scientifics’ Astroscan-Plus with its amazing 3-degrees of sky coverage (or six fill-Moon diameters!) using its 16 power eyepiece. But even that instrument won’t be able to give an "all-at-once" view if the comet lives up to expectations. Yet what it will show should be spectacular! Sweep along the length of the tail and watch it change in size and appearance from day-to-day. And be sure to examine the head of the comet using the scope’s higher power 30x eyepiece.
Going back to December 1st, there’s more to see in the dawn sky in addition to the comet itself that morning. A very thin, hairline crescent Moon lies to its upper right in the southeast—and between them the planet Mercury and above it Saturn. By the next morning the Moon will have completely disappeared, being at its new phase. Mercury drops lower in the sky each day and becomes harder to see while Saturn slowly climbs higher. All in all, quite a show well worth getting up before dawn on December mornings. Hopefully Comet ISON will indeed live up to its expectations and become the "Comet of the Century"!
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.