Image Processing - Finding Asteroids
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Finding Asteroids

If you have done the Asteroids project, you may have learned how to identify asteroids from their movements. We are now going to learn another way to identify moving objects, through a process called "blinking". In 1930, Clyde Tombaugh blinked images to discover Pluto. Along with asteroids and new planets, blinking can also be used to discover other objects such as supernovae, novae, and variable stars.

Blinking images means quickly switching between two images. IRIS can do this for you automatically. You will be able to see changes between the two images, such as an object moving back and forth. The moving object could be an asteroid.

You may see some objects get brighter or dimmer. If you are alternating two filters, such as the red and the green, this tells you that an object is brighter in one color than in the other. If you are looking at two different images taken through the same filter but at different times, this tells you the object is actually getting brighter or dimmer.

The procedure for blinking images is lengthy, but it's worth it!

Exercise 6. The steps you must follow to blink images are outlined below.

1. Retrieve the data using the Object Explorer. Look in the area around ra = 196.18, dec = 11.425. Select corrected frames in the r and g bands (they are on opposite ends of the camera, so the most time passes between the r and g bands, making it easier to find asteroids). Return the files as a .zip file. Unzip the files into your Iris image directory. Rename the files so they are easy to remember. Be sure the filename ends with the .fts extension.

2. Align the fields, like you did when you made the tricolor image. Pick an easily identifiable landmark star.

3. You are now ready to blink the images! Click on the in the toolbar. This button will bring up a small command box. Type the blink command. The blink command has the format:

blink image#1 image#2 delay

For image#1 and image#2, type the filenames for the red and green images (no .fts extension on the end, and be sure they are in your default directory). "Delay" is how long the images stay on the screen before switching, given in milliseconds. Try 200 - 300 for the delay (this will give you a 0.2 to 0.3 second delay). You can change the delay later if you like. To stop the images from blinking, type the command blinkoff.

All of the objects in the images should remain stationary, except for the asteroids. Find the asteroid(s)! Some objects may get brighter or dimmer but not move. That is all right. Some objects are brighter in the green or red filter.

Exercise 7. Open the Navigation tool. Use the zoom buttons (the magnifying glasses) and the NWSE buttons to look through the sky until you find a field you like. Click on any object in the field, then click on Explore to open the Object Explorer. Get the g and r FITS images for that field. Use the blink command to search for asteroids. You may need to adjust the max and min values to find dim asteroids. There is at least one asteroid in almost every field, so you should find something!