I am not aware of any. It does not go through "crescent" and "half" phases like our moon, because it is beyond earth's orbit, so it cannot have (from our view) "phases". And in and of itself, Neptune is one of the most featureless and uninteresting planets to view, much like Uranus.
8 phases.
The changes in shape that the moon goes through are called phases.
It takes one month for the Moon to go through all of its phases one time.
every 29.53 days
Yes
Are sisters won't tell us
29.5 days
Yes.
every four years
Mercury, being an inner planet, does not exhibit phases like the moon does. However, it does appear to go through phases when observed from Earth due to its changing position relative to the Sun.
Nobody's likely to go TO Neptune; at best, robot spacecraft might go BY it and take readings. Anything trying to "land" on Neptune would drop through thousands of miles of increasingly thick atmosphere until it was crushed.
about 5 years