Ok...I'll take a stab...entirely from memory, and its been a *long* time since I looked at the numbers...
If you were on the surface of the Moon, how big would Earth appear in your sky compared to the full Moon from the surface of Earth?
Earths diameter is not quite three times that of the moon, if memory serves. Hence...by the terms of your yardstick, earth would be three times (diameters) the size of the moon as seen from earth.
And now for the other marketing materials I need—
How big would:
Mars appear from the surface of its moon Phobos?
The moons of Mars orbit very close in; if I remember right they have an orbital period measured in terms of days. Mars is quite a bit smaller than earth, but even so, from Phobos, Mars would fill up a dang big chunk of the sky.
Depending on where you were at on Phobos, it might come close to filling up the entire sky.
Jupiter appear from the surface of its moon Io?
Jupiter, largest planet of the solar system, Io, closest in of its major moons. Depending on the observers position, it would just about fill up the sky.
Saturn appear from the surface of its moon Tethys?
drawing a blank here. Saturn is the second largest planet in the solar system, but I don't recollect the specifics of Tethys orbit right off.
Uranus appear from the surface of its moon Ariel?
Memory serves, the moons of Uranus are all small and close in, relatively speaking. I'd have to go with `bigger than earth as seen from the moon'.
Neptune appear from the surface of its moon Triton?
If memory serves, Triton has a highly eccentric orbit. Hence, the size of Neptune as seen from Triton would depend on Tritons orbital position at that point in time. As gas giants go, Neptune ain't all that big, so at the remote end, a bit smaller than earth seen from the moon; at the close end...it wouldn't fill the sky, but it would take up a big chunk of it.
Pluto appear from the surface of its moon Charon?
If memory serves (isn't there a space probe due to arrive there sometime in the next eight or ten years?) Pluto and Charon are both small (smaller than earths moon), but they also orbit very close to each other. Hence, from the right vantage, Pluto should fill most of the sky as seen from Charon...though that far out, there ain't a lot of light out there anyhow.