13. Identifying the Contours of a Planetary Image
IRIS can be used to identify the contours or outline of a planetary disc (such as the image of Jupiter, the Sun, or the moon) which can be used in precise stacking of images based on image outline. This is done by first selecting the image of the planet, and running the command circle followed by a threshold value. In the example below, the command load r1 was used to display the first image of Jupiter’s r sequence, and then the disc of the planet was selected with the mouse.
For the software to identify the outline of the planet’s disc, run the command circle, followed by a threshold value that you need to determine through trial-and-error. In the example below, the command circle 15 was run and then the software calculates the circle that will best fit the contours, for the threshold value of 15. Running the command circle 15 again toggles the circle displayed on and off. IRIS calculates the center of the image based on the circle drawn.
Try entering different threshold values until you find a circle that is slightly smaller than the disk, as it tends to help locate the center of the image better. In the example below, I used 30 as the threshold value and run the command circle 30.
We take note of the threshold value 30 as it will be needed when we run the command to register the planet’s image by drawing outlines around the image disk.
Night Sky in Focus | Astronomy and Amateur Radio © Anthony Urbano | Manila, Philippines