Tutorials: FITS Header, Aligning and Animating Images, Stacking Images

Exercise

The images needed for this portion of the lab are located in LabImage/Asteroid/3_Juno/

The images were taken over two days, and the images are in different folders.

  1. Open one image from each observation of 3 Juno (folder 105 or 106), and determine when the observations were taken from the FITS header window. You should record the observation dates for both sets of images.

    You can find the RA and Dec within an image by using the information window (ctrl+i). Change the ‘mode’ option to Astrometric and now the information window will display the RA and Dec of whatever object you hover over with the mouse.
     
  2. What is the RA and Dec of 3 Juno on each day?
     
  3. Open the remaining images of 3 Juno in one of the folders and follow the Guideposts below to animate your images. We will align these images using the Auto Star Matching option. It is very important that you only have open images from one day, otherwise the auto star matching will fail.
     
  4. Why is it important to align your images to the star field? If you’re unsure, try aligning your images using the asteroid and see what happens.
     
  5. What constellation was 3 Juno in during these observations?
     
  6. The semi major axis of 3 Juno’s orbit is 2.67 AU. How long does it take to complete one orbit around the Sun?

Guideposts

When was this image taken?

Astronomical images are usually in FITS format, which is essentially a bitmap (i.e. a large, uncompressed image) with a bunch of text attached that gives important information about the image such as when and how it was taken, where the telescope was pointing, etc. You can view this information by selecting View -> FITS Header Window from the menu.  Some of the noteworthy pieces of information are: OBJECT - the name of the object the telescope was looking at; DATE-OBS - the date and time the picture was taken; EXPTIME, FILTER - the exposure time in seconds and filter used.

align
Aligning Images

Maxim has a tool that can align images that are slightly offset from one another. SelectProcess -> Align from the menu. Select the names of the images you want to align and click on the right arrow to add them to the list, then click OK. The Align Images window will appear. Here, you have several Alignment Modes from which you can choose.   For these particular images, 'Auto-star matching' works well. You can preview how well your Alignment Mode is working by selecting 'Overlay All Images' before you proceed.  Once you've selected your Alignment Mode, click OK.  Notice the background stars of both images are now mapped to identical (x,y) pixel coordinates.

Animating/Stacking Images

Once you have aligned images, you can animate them to see the motion of an object. This is useful when you are looking for a moving object that is hard to distinguish from background stars in a single image. You can also stack images, which is helpful if you are trying to measure how much an object moved between successive images. To perform these functions, select View -> Animate or Process -> Stack from the menu.