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Brady Yoon
2004-May-13, 02:43 PM
What cycle of phases do the planets outside Earth's orbit show? For example, does Jupiter remain full all throughout the year or does its phase change like Venus and Mercury?

Thanks

tlbs101
2004-May-13, 03:01 PM
Any planet farther away from Earth than the Sun will always be "full".

Only planets closer to the Sun than the Earth (including the Moon for ~1/2 of its orbit) can be aligned relative to the Earth and Sun to exhibit "phases".

ngc3314
2004-May-13, 03:18 PM
Any planet farther away from Earth than the Sun will always be "full".

Only planets closer to the Sun than the Earth (including the Moon for ~1/2 of its orbit) can be aligned relative to the Earth and Sun to exhibit "phases".

Slight correction: outer planets can never have quarter or crescent phases - they always appear as some kind of gibbous-to-full form. The difference is most noticeable for the closer ones - at quadrature (seen 90 degrees from the Sun), Mars is very noticeably less than full. You have to look pretty carefully to see the phase difference for Jupiter, and for Saturn it shows up mostly in where the shadow of the planet falls on te ring system.