The "ruler" measurement seems to provide a # of miles or Km as if we were on the surface of earth. The "arcsec" reading seems to be of greater value - but we need a "range to object" reading as well as the arcsec reading in order to calculate size.

We used Google Sky for a elementary school science fair project.
We struggled to come up with useful projects since we lacked key data.
We compared the arcsec reading for different planets when they each completely filled the screen, but the calculation was off vs. reality....

Examples Additions:
How about good "ruler" tools to compare the size of planets?
What is the focal length or the magnification of each view?
We could compare the relative on-screen size of planets when at the same
magnification to then create a chart of relative sizes and then compare that to known truth... Could we measure asteroids over several days and calculate an orbit?
How about luminosity of each star at a certain magnification?
Then we could create a table of certain stars light intensity and graph it....
Using that and location in certain constelations, could we it is in the milky way in comparison to our solar system...? Estimate a star's age?

It would be really nice if experienced telescope enthusiasts coiuld brainstorm on what else could be added so that students could come up with hypothesis based experiments and use Google Sky to test their question.

Great tool overall - but I think this challenge to the user community might create good results and better scientific usage in schools beyond the "cool" and "wow" factor. Maybe Google should offer a $1,000 prize to the best science fair project each year that uses Earth or Sky ??

wr/ Dave Lechner
Maryland