What tracking rate for comets?

[StuartT]

Is there a way of getting my mount to track comet Leonard for some astrophotography? How much would its motion relative to the stars cause problems for exposures of 10-20 sec at 800mm FL?

Are data on cometary motion published somewhere? 

[vlaiv]

Speed of comet against background depends on where it is currently on its trajectory around the Sun - closer it is - faster it will be going if its path is elliptical. It will also depend on position relative to Earth as Earth is also orbiting around the Sun.

You can take for example Stellarium and calculate it's speed in arc seconds per hour or some similar unit and figure out how much it will move in one exposure.

For fast moving comets - you can actually guide on comet itself - but then stars will streak.

If you decide to image it tonight - well, you are in for a treat - it is crossing M3 tonight - or rather in the morning.

Here is info - I plotted two markers at comet position in one hour span and it moves ~6' 23" in that period so it is 6*60" + 23" = 383" per hour or 383" per 3600 seconds. Speed of movement is therefore ~ 0.10639"/s.

Now you can calculate how much trailing you'll get in 10s exposure - about 1". Further it depends on your working resolution - how much that will be in pixels.

I think you'll be fine with exposures of 10-20 seconds as that will result in ~1px of trailing (provided you are using reasonable sampling rate between 1" and 2" /px).

For longer exposures - I'd advise to guide on comet itself.

 

 

[StuartT]

3 hours ago, vlaiv said:

Speed of comet against background depends on where it is currently on its trajectory around the Sun - closer it is - faster it will be going if its path is elliptical. It will also depend on position relative to Earth as Earth is also orbiting around the Sun.

You can take for example Stellarium and calculate it's speed in arc seconds per hour or some similar unit and figure out how much it will move in one exposure.

For fast moving comets - you can actually guide on comet itself - but then stars will streak.

If you decide to image it tonight - well, you are in for a treat - it is crossing M3 tonight - or rather in the morning.

Here is info - I plotted two markers at comet position in one hour span and it moves ~6' 23" in that period so it is 6*60" + 23" = 383" per hour or 383" per 3600 seconds. Speed of movement is therefore ~ 0.10639"/s.

Now you can calculate how much trailing you'll get in 10s exposure - about 1". Further it depends on your working resolution - how much that will be in pixels.

I think you'll be fine with exposures of 10-20 seconds as that will result in ~1px of trailing (provided you are using reasonable sampling rate between 1" and 2" /px).

For longer exposures - I'd advise to guide on comet itself.

 

 

Thanks so much vlaiv! This is really helpful.

In fact, it looks like it will be in a perfect spot for my telescope viewing position (as it is clear to the east and south) in the morning at 4am to sunrise and at a good elevation (about 43°)

I gather the coma is about 8' wide. My scope has a FOV radius of about 1° so I hope it will be big enough to get a decent image.

All I need now is a clear night! ("all" he says! 🤣)

[Elp]

Was looking forward to the M3 crossover but as usual it's 100% cloudy, it always is when there's something unique to see.

[StuartT]

13 hours ago, Elp said:

Was looking forward to the M3 crossover but as usual it's 100% cloudy, it always is when there's something unique to see.

yep. that's how it works.

I would be happy to see the damn thing at all! I set the alarm for 4:30am today just in case, but it was totally cloudy. I'm going to do the same over the weekend 🤞

[Elp]

I could have gone outside on Wednesday as it was clear all night but I thought, nah too cold. Oh well.

Here's hoping for sometime soon.

[Laurieast]

I hope somebody caught this event on camera!

[mcrowle]

Great to see, there are some fantastic captures of the M3 encounter in the Spaceweather.com Comet gallery: https://spaceweathergallery.com/comet_gallery.html

No chance here in Cornwall!

Regards, Mike.