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
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
The procedure for blinking images is lengthy, but it's worth it!
The steps you must follow to blink images are outlined below.
1. Retrieve the data using the
Look in the area around ra = 15.5, dec = 0.5.
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!