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Identifying a star field

Beardy Bob

By Beardy Bob
in Imaging - Discussion

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Beardy Bob

Beardy Bob

Posted
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OK, here's the background...

I spent ages manually focusing a lens pointing at around about the Spaghetti Nebula. Then I took ages taking shots with a Ha filter to try and find it. Knowing that it is pretty dim I needed to take pretty long exposures to have enough data to actually see if I was on target, which is VERY time consuming. Indeed, in the two/three hours I was out doing this the night before last the clouds rolled in before I managed to find it, and now I have to start the whole rigmarole again!

And here's the rather convoluted question...

Is there some kind of huge database through which you can input your image (along with a few focal length/chip size details) to find out where you were in the sky (and from there how far you were away from your target and in which direction)?

Hope that makes sense. I've tried the other way around i.e. zooming into a stellarium program to match the FOV of my chip/lens combo and trying to find a matching star field, but it's an impossible task!

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IanL

IanL

Posted
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You don't say what your gear is, but if it is capable of being driven via ASCOM on a Windows laptop, AstroTortilla is what you are looking for. Here's our own lovely 14 page SGL thread on the subject:

http://stargazerslou...-astrotortilla/

You can read about it and download here:

http://sourceforge.n.../astrotortilla/

It uses the astrometry.net plate solving engine (which it installs for you), plus you need a bunch of (large) index files which it can also download. It connects to a number of astro-imaging applications to capture short (5 - 10 second) exposures and solve them. Once it knows where you are pointing it will issue a "Sync" via ASCOM to your scope's handset or driver software to update the pointing model.

You can get it to automate the process of finding a target in a number of ways; tell it where to point, it will iteratively snap an image, solve it, update the pointing model and slew the the adjusted location, snap, solve, point, etc. until it gets within an arcsecond or whatever you define of the point.

A really neat way of doing that is to load a previous image (yours or someone else's), have it solve the image and get the scope on the same target, untouched by human hand. Once you have done a basic polar alignment, you don't even need to do a one/two/three star alignment. AT will work it all out for you and build an alignment model in your scope's driver software as it goes.

Even if your capture software is not compatible with AT, it has a 'file dialog' camera so you just manually take snapshots and then select them from disk.

If you are just working manually (e.g. camera and tripod), you could (say) use AT, plus the EQMOD simulator and CdC or Stellarium. Capture an image to the laptop, solve it in AT and have it repoint the simulated telescope, which will update the reticule location in the planetarium and you'll know exactly where the camera is pointing and have some idea of how to adjust it.

If you are really old school, just have AT solve the image and you can look up the reported RA and Dec in your Sky Atlas 2000 or whatever! If you like, you can just fire up the CygWin console and use the astrometry.net 'solve-field' command with appropriate options.

You can definitely run the astrometry.net engine on Linux variants as that is what it is built for (AT puts a Windows GUI on the solve process and hooks into the capature software and Ascom, but uses CygWin to run the unix-based solving engine). Not sure what your options are for a front end though. Being Linux bound to be several add-ons out there.

If you are a Mac user take a look at this thread which does the same sort of job but with scripts and the astrometry.net solver:

AT does take a bit of setting up and trial and error to get reliable solves, but I have managed to get some of my plates solved in 6.5 seconds now, but even 18 seconds or a minute is a real time saver when trying to get going. You can do most of the testing and learning during the daytime if you take some snapshots of known targets. Now AT is up to version 0.5 the documentation, software and community knowledge is improving rapidly to get new users up to speed.

The Flickr upload/solve is actually driven by astrometry.net and you can just go straight to that site and upload images if you want to try the process out or solve your existing images online. Either way, online solves take a few minutes to complete usually, so you'd be better having a local solution.

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chrisshillito

chrisshillito

Posted
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Once you have done a basic polar alignment, you don't even need to do a one/two/three star alignment. AT will work it all out for you and build an alignment model in your scope's driver software as it goes.

Strictly speaking an ASCOM Sync should only shift an existing alignment model to align with the sync point - not create or change the model itself. We bent the rules with EQMOD when we gave it the "append on sync" option (which was so popular it became the default mode of operation) - other mount drivers may not have followed our lead though.

Chris.

Chris.

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jazzysam

jazzysam

Posted
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Hi Beardy Bob,

you might be aware of this already, but Maxim DL comes with a plate solving program called PinPoint (light edition) by dc3.

i regularly use it to work out where I am; I take a luminance exposure first at 4bin, plate solve so that I know exactly where I am, move scope then plate solve as many times as necessary until I'm exactly where I want to be. At that point, I start taking long Ha subs, knowing I'm in the right place.

you can buy pinpoint separately (uses the GSC11 astro database), but its expensive compared to getting the add-on to Maxim. The nice thing is that you can get a previously taken image (from previous session), plate solve it, and the get maxim to send scope to that precise location (then plate solve again to confirm/refine position). It takes all the guesswork out completely.

CCDautopilot makes use of plate solving for automation of target positioning/imaging. You will note that the two options are pinpoint and the software bisque option.

hope this is of interest. Let me know if you would like links to the suppliers...

clear skies,

Sam

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IanL

IanL

Posted
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Strictly speaking an ASCOM Sync should only shift an existing alignment model to align with the sync point - not create or change the model itself. We bent the rules with EQMOD when we gave it the "append on sync" option (which was so popular it became the default mode of operation) - other mount drivers may not have followed our lead though.

Thanks for the clarification Chris.

I had AT up and running with EQMOD on Saturday night (first weekend clear skies since the middle of December for me). Had a bit of a false start with the Canon (disconnected unexpectedly, took ages for me to figure out that it was staying on when I powered it off. Was still trying to download to the laptop and the display was turned off!)

Apart from that, it was a couple of minutes to do a polar alignment, and then I used AT to get on target in three minutes (including tweaking the focus), didn't do an alignment at all. Compared to the previous times out amazing results. Should be even quicker next time since I have bookmarked my target in AT.

Whichever package you choose, plate solving is the future!

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chrisshillito

chrisshillito

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.... and then I used AT to get on target in three minutes (including tweaking the focus), didn't do an alignment at all

Well you did, but you've just automated the process :smiley: . AT is doing the alignment for you every time it syncs and EQMOD is using using those alignment points to correct the slew every time AT asks it to move.

Chris.

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IanL

IanL

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Well you did, but you've just automated the process :smiley: . AT is doing the alignment for you every time it syncs and EQMOD is using using those alignment points to correct the slew every time AT asks it to move.

That's what I mean by 'I didn't do an alignment', the software did, and it didn't even take long enough for me to go inside and make a cup of tea even though I was a mere bystander in the process and probably should have done.

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