Plate solving is a technique that I know is going to change astrophotography for you. It did for me! In this post, we will look at what it is, how it works, and why you should try it.
Plate-solving will require you to use a laptop while you image, but the software you use will be free and easy once you set it up and use it a couple of times.
For a few years, I was using an alt-az mount with my telescope, and to locate an object in the sky, I went through a long process. This is what I was doing:
- I aligned my telescope to two stars using the GOTO system of my Celestron 130slt mount and hand control unit.
- I selected the target on the hand control, and the telescope moved to the position where it believed the object was.
- I couldn’t see anything through the eyepiece, so I wasn’t sure if my telescope was pointing at the target or not.
- I took a test shot with my camera and if I was lucky the object was in the frame.
- If the object was not in the frame, I had to randomly move the telescope one way or the other, left, right, or up and down, to try to find it.
- If I couldn’t find it, I tried to see if I could identify any pattern of the stars, and then I would be able to move the telescope a bit in one direction to get the object in view.
- Once the object was in the frame, I had to centre it by moving the telescope in one or two directions, step by step. I would count three steps this way (pressing the hand control three times to move in three steps) or five steps that way until I finally got a photo with my target in the centre of my camera field of view.
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As you can probably guess, this wasted so much time when I could have been imaging. A few times, for whatever reason, I lost the target and had to find it again. After a meridian flip, for example, the target was not visible in my photo, and I had to repeat the whole process to relocate it. On one occasion, I spent an hour or more and could not find the object, which was the Helix Nebula, after the flip. I was freezing cold that night and just gave up, wasting a perfectly clear night.
This process was very painful, and I needed something better.
Plate solving was the solution, and I have been using it ever since. It regularly takes me just 5 minutes to find and centre any astronomical object so that I can begin my imaging session.
What is plate solving?
So what is plate solving, and how does it work?
Plate solving is a method that astronomers use to find an object in the sky based on its coordinates. Every deep sky object that is known has two coordinates, an RA value, and a Dec value. these are similar to the GPS coordinates we use to identify a place but these correspond to a position in the sky.
The Right Ascension value is the latitude and the Declination is the longitude of celestial coordinates. Your telescope, after being correctly aligned, can move to the coordinates specified for a given object and find it. The problem comes when, as usually happens, your telescope is slightly off alignment and misses its target by a fraction. I have found that if my telescope missed by a millimeter this was way off because think about it, these objects are tiny and very far away.
Plate solving does the following:
- it moves the telescope to the coordinates of the object
- it takes a photo with your camera (mine is set to a 20-second exposure for this)
- it compares the stars in the image to a database of images of the sky
- it locates exactly where the telescope is pointed
- from this information, it calculates in what direction and how far the telescope has missed the target
- it moves the telescope to a new position closer to the target
- it takes another picture and compares it to the database again to see if it is now on the target
- if it is close it now tries to put the target in the centre of the field of view
- if it is still not near the target it repeats the process again
- when the target is in the centre of view it stops and you sync in the software program
Now the telescope knows its exact position and is accurately aligned to the night sky and begins to track the object. The above procedure rarely takes me longer than 5 minutes even if the telescope is not aligned before trying this. The first image and solve (calculation to understand where the telescope is pointing) can take as long as 90-100 seconds but after that, it is just a matter of a few seconds for each step after the image is taken.
Plate solving is a key tool for astronomers who want to take beautiful pictures of objects in space. There are a lot of different astrophotography tools that can plate solve, like Astrometry.net, Sequence Generator Pro, and the Astrophotography Tool (APT).
With these tools, you can quickly and easily find where celestial objects are in the sky and move your telescope to get a clear picture of the object.
How to use the plate-solving app in astrophotography tool
APT is a popular tool for astrophotography, and it may also be used to plan an image session or do Meridian Flips, among other things. This software is meant to make astrophotography as easy as possible. It has various features that make taking breathtaking images of the night sky easier than before.
I use USB cables to connect my laptop to my mount, my auto-guiding camera, and my main camera. Once your equipment is set up, you can utilise the software to choose the plate-solving option. Then, APT will take a picture of the night sky and look at it to see where any objects in space are.
Once this is done, APT will reposition your telescope to where the celestial object is in the sky. Then, you can sync this information to your telescope so it knows where it is pointing. APT also includes an automatic tracking mode that enables you to follow the object as it moves across the sky and shoot high-quality images of it. Download APT here.
The easy-to-use interface of APT is one reason to use it to plate solve. The program is easy to use, and it has several extra features, such as a tool to help you focus and an indicator that tells you how long until the next Meridian Flip is needed. APT also works nicely with other software like PHD2, which is a free program that runs auto-guiding software to keep the object from moving even if your tracking mount isn’t accurate.
It’s also a good idea to utilize APT because it is reliable. The program is meant to be stable, so you can trust it to tell you exactly where objects are in the sky. This is especially crucial for astrophotographers who want to shoot high-quality photos of space objects and need to know they can count on their equipment.
Many are using the popular alternative to APT, NINA, although I didn’t manage to find this as easy to set up as APT. It can also do plate solving for you as well as many other tasks.