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Reduce (calibrate) data

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Align and normalize your images

Background

The direction the telescope points changes very slowly because its tracking isn’t perfect. That means you need to specify where a few stars are in the image that ImageJ can then use to line the images up, a process called alignment. In addition, the brightness of the sky itself may change over the course of the evening, especially if the images are taken near sunset or sunrise. The process of scaling the images so that the background level is the same is called normalization.

Open reduced images as a sequence

Before aligning the images you need to open them all in a single window. To do that, open ImageJ and then:

  1. Open a FITS image, any FITS image. Screenshot of crap
  2. Make sure the ImageJ toolbar is on top of the image you just opened, then “Open image sequence in new window” image sequence
  3. Select the folder containing your reduced images. image folder
  4. Check that the number of images is correct and uncheck “Use virtual stack” no stack

Align the images

Aligning is pretty easy. Basically you just need to check a few settings then click on some bright stars in the image and ImageJ does the rest.

The details:

  1. In your image sequence, click on the align button and read the instructions that pop up. align button
  2. Click on a few stars, right click when done to start the alignment process. stars

Normalize your images

Normalizing is pretty easy; just select “Normalize...” from the Process menu. normalize