Being an astronomer, kilometers or miles as an indicator of scale don't mean much on the sky. I am used to think about angular size: the apparent size of an object as viewed from Earth. Typically this is measured in degrees or fraction of degrees: 1 arc-minute = 1/60 of a degree (symbol '); 1 arc-second = 1/3600 of a degree (symbol ").

I would really love to have a scale on GoogleSky that actually shows me an angle. The GoogleSky client does return a measure of the current viewport via the BBOX that it appends onto each networklink request. So, until the Google guys make the change on the sky client itself, I thought it would be nice just to use the BBOX and add a screen overlay with an angular measure.

4 seconds after the camera stops (default) , this kml will recompute the BBOX and generate an angle measure, displaying it on the screen as an overlay on the top left of the screen. This measure is as good as the BBOX and works reasonably well expect around the poles. The angle switches from degrees. to arcmin, to arcseconds accordng to the BBOX scale.

It's simple, but seems to return reasonable numbers, so I thought I'd share it.

Dr. Alberto Conti
Space Telescope Science Institute