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:
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.