A comet passes a planet – October 19, 2014

A very rare astronomical event just happened on the evening of October 19th: comet C/2013 A1 (Siding Spring) passed only 132000 kilometers from the planet Mars, that is almost a third of the Earth-Moon distance. In 2013, when the comet was discovered, the prediction was still hard to compute, and there was a slight chance of an impact; eventually the ephemeris of the comet position were computed from a longer period of time and the chance of the comet hitting Mars were reduced to zero. Still, the event remained as one of the most impressive for both professional and amateur astronomers.

And luckily enough for our latitude (45N) the event was just visible above the horizon.

For “spying” on this cosmic meeting, I had to travel onto darker skies and a location with a low horizon, in the Comana Woods just south of Bucharest, together with my wife and her brother.

The equipment used: TS APO 115mm F/7 Refractor on a NEQ6 equatorial mount, and an ASI120MM camera with Baader UV/IR cut filter.

Half an hour after the Sun went down I’ve managed to align the mount and prepare the acquisition settings. The first target was to see if the comet could be easily visible onto single 15 second frames; after the very first image, the result was positive, despite the rather diffuse aspect of the comet, and it’s +10 magnitude.

I will start (for now) with two animations showing the movement of both the comet and that of the planet Mars among the stars. Both animations are made up from 151 frames, each a 15 second exposure. Each of them shows a different perspective: the first shows the movement of both objects with a fixed background of stars. The second shows the scene as it would be observed by a space probe moving at the same speed as Mars. The planet is overexposed in all of the following images; the apparent size of Mars is of course much smaller.

I’m still trying to get the best out of these noisy images, so better images might appear later on in this post, but until that moment, I’m posting a few images with this event, with different perspectives.

The first shows the background full of stars and the movement of both the comet and Mars among them:

The second shows the movement of the comet (and that of the stars in the background) with Mars in a fixed position. This is perhaps the correct way to show the comet’s approach to the planet. Only some of the frames were used in the image, and thus the distinct shape of the comet is seen onto it’s trajectory in five positions.

And the last (for now) is an image that shows the actual comet onto a moving background. The strange shape of Mars is the result of the planet’s movement.

All of the above images/animations were acquired during a 50 minute period, from 16:30 to 17:20 U.T.

One of the above animations was posted on the AstroInfo page.

Max

(October 20, 2014)