Monday, January 19, 2015

Incredibly Long Comet Tail

Incredibly Long Comet Tail

Lately, if you have been out in the countryside and looked up in the starry sky, you might have noticed not far from the Pleiades star cluster the fuzzy green head of Comet Lovejoy. There's also a hint of a tail, faint but long. Note to sky watchers: It's even longer than you think. Astrophotographers doing long exposures of the comet find that the tail extends an incredible 15o to 20o across the night sky. Alan Dyer, author of "How to Shoot Nightscapes and Timelapses", sends this picture from City of Rocks State Park, New Mexico:

"These images from show just how marvelous Comet Lovejoy's blue ion tail has become, at least to the eye of the camera," says Dyer. " It now stretches back at least 15°, perhaps as much as 20° with 'averted imagination'!" Click here to learn more about Dyer's photo settings.
For reference, a 20o long tail would stretch along the entire length of the Big Dipper, from handle to bowl. It is 40 times as wide as the full Moon.
Many observers have noted the similar colors of the Pleiades and the comet's tail. Both are a beautiful shade of cosmic blue. Despite their similar appearance, however, the two blues come from different physics. The comet's tail is blue because it contains ionized carbon monoxide (CO+), a gas which fluoresces blue in the near-vacuum of interplanetary space. The nebulosity surrounding the Pleiades is blue because grains of interstellar dust embedded in the gas scatter the blue light of hot young stars at the cluster's core.
Need help finding the comet? Check these finder charts from Sky & Telescope. Also, the Minor Planet Center has published an ephemeris for accurate pointing of telescopes.


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