By mid-November, the much-anticipated Comet ISON (C/2012 S1) really began to put on a show. Lagging slightly behind the predicted magnitudes, it experienced an outburst and brightened by a factor of 10 in one day. The comet is now a naked-eye object, visible in twilight in the early morning sky, but with the Moon also hampering the view.
ISON will swoop quite close to the Sun on November 28, some 1.8 million kilometers from our star's surface, which will enable it to light up dramatically.
This gorgeous photo shows the way the appearance of the comet on November 15:
Credit: Damian Peach
To see it this week, you'll need to venture out in the early morning, between 4 a.m. local time and dawn, and look to the southeast, toward the constellation Virgo. Because moonlight makes seeing sky objects harder, you may need a pair of binoculars to pick it up, although the comet now glows at around 4th magnitude, well within the range of being visible with the eye alone.
At midweek, the comet rises 1 hour 50 minutes before the Sun and is positioned south of the bright star Spica, the brightest luminary in Virgo. Nearby lie both the planets Saturn and Mercury, and the comet's motion is of course carrying it rapidly toward the Sun.
This map will show you exactly where to look:
Credit: Astronomy: Richard Talcott and Roen Kelly
In late November, Comet ISON moves its fastest as it flies from Virgo, through Libra and Scorpius, and then heads north into Ophiuchus.
Other comets are visible in the morning sky, too, including the relatively bright Comet Lovejoy (C/2013 R1), which is heading northeastward into Leo Minor, and a famous periodic comet, 2P/Encke, which is very low in the twilight.
Comet ISON will appear as a soft glow, a fuzzball shimmering from the gases released from the comet's frozen nucleus, which measures perhaps two kilometers across, as it increasingly warms in sunlight. The comet's so-called coma, the fuzzy blob you'll see in binoculars or a telescope, spans about 5 arcminutes across. That's one-sixth of the diameter of the Moon. A faint tail drifts away some 0.3°, more than a third of the Moon's diameter, and will be slowly growing over the coming days.
Over the weekend I attended the Arizona Science and Astronomy Expo in Tucson and took part in a comet panel discussion with astronomers David Levy, Steve Larson, Jim Scotti, and Carl Hergenrother -- all comet discoverers. The feeling is that the comet may continue to outburst as fresh ices are exposed to sunlight, which could lead to more dramatic brightening. The comet's tail is already showing several discrete streamers, producing beautiful and elegant images. And the comet has shown a small arc-shaped feature near the inner coma that may be indicative of some fragmenting of the nucleus. This doesn't necessarily mean it will break apart, but rather that areas of different density are warming at different rates and streaming away from the nucleus.
Over the next week, ISON should continue brightening significantly. Keep your eye on the comet and realize that, even if it's subtle, you're witnessing one of nature's most amazing visitations, a rare and distant traveler wafting into the inner solar system, a stranger from the sea of darkness beyond us.
David J. Eicher is Editor-in-Chief of Astronomy magazine, author of 17 books on science and history, and president of the Astronomy Foundation. His book COMETS! Visitors from Deep Space was just published by Cambridge University Press.