If you just bought a go-to mount either to start your astrophotography journey or upgrade from a star tracker, congratulations. Being motorized on both the right ascension and declination axis, go-to mounts have a major advantage over their non go-to counter parts.
Not only do you not have to manually frame your targets like you would with a star tracker, you can harness the abilities of plate solving.
If you have never plate solved a target the concept may sound like a bit of an enigma to you, but its really not as complicated as it seems. In this article I am going to talk about:
- The traditional method of star aligning your mount
- The advantages offered by the alternative method of plate solving
Table of Contents
Method 1: Star Alignment
When you first set up a go-to mount and you’re not using any computer software, the first step after polar aligning the mount is to do a star alignment.
Generally speaking this is done by setting the date, time, and coordinates of your location using the hand controller for your mount. After you’ve done so the mount will give you various stars to choose from, and ask you to center them in the telescopes field of view one at a time.
The reason that we are doing this is that it allows the mount to build a pointing model. Once you correctly show it where several specific stars are in the night sky, it will have a precision data set that it will then use to find other objects in the sky.
When you first power it on, your mount doesn’t naturally know exactly where its pointing on its own. If you skip the star alignment and tell it to go to an object, chances are that its pointing accuracy will be significantly off (unless you get really lucky which is rare).
The biggest take away here in my opinion is that by using this method, you are working for the mount rather than the other way around.
The biggest downside to this method is that it can take a long time especially if you’re new to it. If you are in fact doing this for astrophotography purposes you likely aren’t using an eyepiece with your telescope.
Unless you have a separate finder scope it can be challenging to center a star on a small camera screen at a high level of magnification, or even find the specific star you’re looking for.
This is a method I would use only if you don’t have a laptop, and if you do I would recommend moving on to method 2 as quickly as possible.
Method 2: Plate Solving
Plate solving ultimately achieves the same goal as manual star alignment by building a pointing model for your mount. Whats different about it is that instead of you guiding the mount to specific stars that it asks for, it figures out where its pointing by using software to analyze the stars in an image that you take of a random area of the sky.
The basic process here is as follows:
- polar align your mount
- slew to a random area of the sky
- take a 10 second image
- ask your image acquisition software to plate solve the image
- sync the corresponding coordinates with the mount
- do this a few more times in other areas of the sky
Each time you plate solve one of your test images and sync it with the mount, it tells the mount exactly where its pointing. Once you do this several times, your mount will have pinpoint pointing accuracy.
In using this method you are making the mount and computer software work for you, rather than you working for the mount.
Once you’re proficient with the software, you can have your mount fully acclimated with the sky and have a pointing model built in a matter of minutes.
What’s also great about using this method is that you will know that your target is dead center before you start imaging. Most popular pieces of imaging software like NINA, will automate this process for you. Even if the target is a bit off center when the mount initially slews to it. After the slew it will take a test exposure, solve it, and bring the target to the center of the frame.
What Will I Need to Make This Work?
Skywatcher/Synta Mounts
If you are using a Skywatcher go-to mount you will need to download the necessary software, EQMod being the most commonly used. I recommend this tutorial from Light Vortex Astronomy:
iOptron Mounts
You will need to download the necessary drivers and the iOptron Commander here: Support (ioptron.com)
Image Acquisition Software
You are going to need to choose what image acquisition software that you would like to use. This is basically the software that you are going to use to plate solve, frame, focus, and physically take the sub exposures for your images. There are many to choose from including:
- APT which stands for Astrophotography tool
- SGP which stands for Sequence Generator Pro
- NINA which stands for Nighttime Imaging ‘N’ Astronomy
I have used both APT and NINA and would without a doubt, 100% use NINA. You can download it for free here: Nighttime Imaging ‘N’ Astronomy – An astrophotography imaging suite (nighttime-imaging.eu)
Lastly you’re going to need the actual plate solving software and the corresponding star databases that it will use to analyze your images. I personally recommend ASTAP which can be downloaded here: ASTAP, Astrometric Stacking Program (hnsky.org)
Conclusion
Plate solving really isn’t as complicated as it sounds, its just a technical term for determining RA and Declination coordinates based on the position of the stars in a short exposure image.
Either of the methods discussed will ultimately achieve a similar goal but I would encourage you to take advantage of plate solving. Not only is plate solving a major quality of life improvement in and of itself, it’s just one of the countless advantages of using computer software to control your imaging process.
Start with plate solving and before you know it you’ll be using NINA to automate the entire imaging process for you while you catch up on something we have all been missing a bit of, sleep.
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