Full Guide: Plate solving [2021 Edition]


Plate solving ( AKA astrometric solving )is used to accurately center an object in the sky within the field of view of your telescope, one does not need a high resolution pointing solution. For the most part, lower range telescope mounts do not provide the very best pointing accuracy especially when coupled with optical issues such as: mirror flop, tube flexure, differential flexure, nonorthogonality, declination axis to polar axis misalignment and more.

What Is Plate Solving?

A function developed by professional astronomers in order to concisely center the telescope’s field of view in the night sky on a given point. This is especially important when the target is a very small object a few arcseconds across such as an asteroid, comet, exoplanet, star..

How Do I Plate Solve My Images?

Plate solving, nowadays, is done exclusively using computers and software


This can be done using manual controls at the telescope. You can simply:

  1. Point your telescope at an arbitrary location in the sky. Make sure you can see some stars.
  2. depending on your pixel scale, snap a 10 to 30 seconds long exposure
  3. Using your preferred software, plate solve your image
  4. After a successful solve, you should receive information such as:
    1. Your focal length
    2. Pixel scale
    3. Center pixel’s calculated right ascension and declination
    4. Image orientation in the sky


Most known automation software can plate solve automatically, if your gear is set up properly in SGPpro, N.I.N.A, The SkyX, Voyager or MaxinDL, PRISM etc..

Since we use and support PRISM v10, we will use it instead

  1. Connect your camera and telescope and slew to an arbitrary location in the night sky where there is an abundance of stars. We recommend pointing somewhere along the galactic equator. This will give us a great number of stars to plate solve with.
  2. Inspect the downloaded image and make sure that:
    1. There are plenty of stars(we recommend a minimum of 30)
    2. The stars are in a good shape, roundish is fine. If the stars are streaks due to a tracking error, the plate solving might not work
    3. Your mount is tracking
    4. There isn’t too much noise. Cooling the camera, if available, might lower the noise substantially. Applying a dark or an autodark will provide the most benefit.
    5. The image has a valid: date/time, RA and DEC coordinates.
  3. Plate solve the image:
    1. Local solving:
      1. Main menu > Analysis > Plate Solving > Single Image or press CTRL+U on your keyboard
      2. Make sure the RA, DEC and

What Are The Most Common Plate Solving Issues?

We can narrow down the issues to a few culprits:

  • Wrong focal length: This is the most common problem amateur astronomers face. If the telescope’s focal length is wrong, the program might need be able to find the location of your telescope in space since the relationship between the measured stars and those in the comparison star catalog will not match
  • Wrong pixel size: This is especially important because it help the plate solving program understand the relationship between the measured stars.
  • No RA/DEC coordinates: If the telescope is not connected to the computer when you snap a picture to solve, the right ascension and declination will most likely not be recorded in the FITS header.
  • Field curvature: Like uncorrected refracting telescopes, stars can get extremely elongated in the corners
    • Pro tip: Crop the image by only using the center %50.
  • The image is too noisy: In order to solve an image successfully, your chosen program will extract the stars from the image by comparing the ADU level of a collection of pixels compared to the calculated background. If you are image is too noisy, you need to clean it using using your favorite noise reduction tool. in PRISM, you can just use a median filter and a 5×5 kernel to get an awesomely clean image like the example below

Final Thoughts

Plate solving is an incredible tool for both amateur and professional astronomers to always home in on the chosen target to within a fraction of an arcsecond.

Once set up properly using this extensive guide, the astronomer can automatically image all night whilst being on target constantly and consistently.


successful plate solving of Messier 51

 Video Tutorial


Plate solving

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