Gustavo Muler

Many of the readers of this blog have already seen the latest images of comet C/2010 X1. On them, the tail of the comet extends all of 1 minute of arc. Is the comet’s tail actually small or is it simply an optical illusion? For my calculations I used Gustavo Muler’s picture which he obtained March 7. Unfortunately before opposition of the comet, we were not able to get an image with any large telescopes – the camera on the two-meter Faulkes Telescope North (FTN), went off-line.

As such, we’ll return to the image we have. On approach to opposition, when the comet, Earth, and Sun are lined up (that is, the C-S-E angle is close to 180°), the comet’s tail is practically hidden from view for the Earthly observer, as the tails of the comet are pointed away from the Sun. At the time the image was taken, we saw the tail at an angle of 2.75°! Taking the length of the projection of the tail as one minute of arc, and solving the triangle, we see the actual length of the tail has already exceeded 900,000 km! Although, in fact, the tail has to be still bigger, as Gustavo used a 30-cm telescope, knowing that if he had photographed the comet with a two-meter telescope, we would have seen fainter fragments of the comet’s tail.

If, on March 7, we had been able to see the comet’s tail in profile, its length on the image would have been in excess of 10 arc minutes. Right now, the comet is approaching opposition, and we have a good chance of getting images of the comet’s coma. Maybe we can also do that on large telescopes.

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