To open this dialog, click 
on the Aperture Photometry Toolbar.
Aperture Photometry Preferences
Astronomy Module
The Aperture Photometry Preferences dialog is used to configure the aperture Photometry command. Specific Property pages organize similar commands or procedures.
To open this dialog, click on the Aperture Photometry Toolbar.
When you are finished making changes, click [Apply] or [OK] to accept them.