A comet known as Comet 103P/Hartley 2 is going to pass at its closest to the Earth since its discovery in 1986, and the visit will be one of the nearest by a comet in the last few centuries.
Unfortunately, says Jim Todd, the planetarium manager at OMSI in Portland, the Wednesday, Oct. 20, visit will be dimmed by a nearly full moon, if not cloudy skies.
For the past few weeks, Hartley 2 has been fairly dim at magnitude 5 or 6, best viewed on very dark and moonless nights for experienced observers. But in the coming days, the comet is expected to be barely visible to the unaided eye, best spotted with binoculars and telescopes.
Unfortunately, the next full moon will be on Friday, Oct. 22, and will make the viewing of Hartley 2 tougher for the rest of the month.
During the week of Oct. 18, the best time to look for the comet will be at dawn when it is high above the northeast horizon. The fuzzy visitor will pass by the brilliant star Capella in the constellation Auriga.
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On Wednesday the comet will be 6 degrees to the lower right of Capella. At this time, it will be 0.12 astronomical units from Earth and at a magnitude of 4, which is about the brightness of the stars in the handle of Ursa Minor, the Little Dipper.
Look for a faint fuzzy patch, the nucleus. Viewing will be best through binoculars. The comet’s kryptonite green halo is diffuse and can be difficult locate.
Toward the end of the month, the comet will be lower in the constellation of Gemini.
By November, Hartley 2 will be fading in view as it moves near Sirius, away from both the Sun and Earth. On Nov. 4, a NASA EPOXI spacecraft, a continuation of the Deep Impact mission, will fly by the comet’s small nucleus, which is estimated to be only a mile in diameter. The probe will take pictures and other data at some 600 miles.