This sequence of radar images of Comet 46P/Wirtanen from Dec. 15 shows apparent rotation of the nucleus in a counter-clockwise direction. The vertical axis is distance in the line-of-sight (15m/pixel) and the horizontal axis is in Doppler velocity from the comet’s rotation. The nucleus rotates once every 8.9 hours, determined from optical images. This movie covers 1.4 hours of the comet’s rotation. By combining images taken over several days, scientists can construct a shape model of the comet nucleus.
Arecibo Observatory/NASA/NSF
2018-12-05
Sources: <a rel="nofollow" class="external free" href="http://www.naic.edu/~pradar/press/dec18obs.php">http://www.naic.edu/~pradar/press/dec18obs.php</a> and <a rel="nofollow" class="external free" href="https://uanews.arizona.edu/story/ua-researcher-captures-rare-radar-images-comet-46pwirtanen">https://uanews.arizona.edu/story/ua-researcher-captures-rare-radar-images-comet-46pwirtanen</a><br>Direct image link: <a rel="nofollow" class="external free" href="http://www.naic.edu/~pradar/images/Comet46P_15dec18UT.gif">http://www.naic.edu/~pradar/images/Comet46P_15dec18UT.gif</a>