PWT back on sky - comet ISON moving slowly

2 April 2013 by Fraser Clarke

Comet ISON on 1st April 2013

M97 - The Owl Nebula717.78 KB

After nearly two months offline due to a broken drive motor, the Philip Wetton Telescope is now back observing the night sky! This has enabled us to take the next image in our Comet ISON project, which we started at Stargazing Oxford back in January. It looks like the coma and tail have got a bit bigger since we last saw it in late January. We've also started getting data for other projects, and at the bottom of the page there's a sneak peak at a future 'pretty pic'...

To get the telescope working again, we had to replace the motor in the declination drive of the telescope. The original motor burnt out in early February, leaving us unable to move the telescope "up and down". That specific motor isn't made any more, and the last time the UK dealer saw a spare was five years ago! So, we've had to re-engineer the whole drive, using a different motor/gearbox/encoder combination which would fool the telescope control system into thinking nothing had changed. After quite a bit of fun counting gear teeth, measuring screw holes, sensing encoder pulses, calculating gear-ratios, and converting electrical wiring, it all worked second time... First time it worked, but the telescope went the wrong way! We fixed it in true sci-fi engineering style by simply "reversing the polarity"! (Also known as soldering the wires on the other way round...)

So, with a working telescope, we can get back on our comet ISON project, and see what's changed since we last looked back in January. Well, the answer is 'not much'!! The comet, right in the middle of the image above, is still a long way out from the Sun, and the coma and tail are still not very big. They do look a bit bigger than in January, though as it was very near a bright star when we took the image last night, it's quite hard to tell. We'll have a look again tonight, weather permitting.

The comet is now actually moving slower than it was last time, and you can see that the stars are less trailed than they were in the previous image. This is not because the comet itself has slowed down (in fact it speeds up as it gets closer to the Sun), but just that our motion around the Sun makes the comet appear to move more slowly. In fact next week the comet will appear to stand still, and then start moving backwards, as we see it from the Earth. The comet, the still small fuzzy object in the middle of the image above, is now moving slowly around the border between Auriga and Gemini.

M97, The Owl Nebula: Owl nebula in H-alpha (Green), OIII (Blue) and SII (Red) taken with the PWT on 1st April 2013

Now that the telescope is operational again, it is going to start working through its backlog of observations. Last night was lovely and clear all night, and the telescope took about 8 hours worth of data on various targets. One was the Owl nebula (M97), a pretty planetary nebula we've got queued up to make a nice image of. So here's a bonus quick-pic taken last night. This is only 1 hour of observation in each of the three colours -- there are another 20 hours of observations due to be taken before the image is properly finished! Still, it's a good start, and good to have the telescope taking data again!

Categories: stargazing | Comet ISON | 2013 | PWT