God of the sea (Greek: Poseidon)
Neptune is the outer-most gas giant and the eighth planet.
Like the other gas giants it is mostly Hydrogen and Helium.
A small amount of methane in it's atmosphere absorbs
the longer wavelengths leaving the planet with it's
beautiful blue appearance. Neptune's atmosphere is much
more active than Uranus'. It had a great dark spot much
like Jupiter's Red Spot. It seems to have disappeared since
the Voyager encounter 8 years ago. Neptune is more
dynamic than bland Uranus, showing much more details in
it's clouds. Neptune has an internal heat source that drives
it. What the source of the heat is, is not clear. It radiates
as much heat as Uranus but is twice as far from the sun.
1846. It was actually 'discovered' mathematically. Continuing
observations of Uranus indicated something was wrong. It
was not where it was predicted. The conclusion was that
something was pulling Uranus off-course. Two
mathematicians working independently deduced possible
locations, for this hypothetical body causing Uranus'
misbehavior. The two co-discoverers were John Couch Adams
and Urbain Jean Joseph Le Verrier who both predicted
Neptune's position with remarkable accuracy. It was within
minutes that observers Johann Gottfried Galle and Heinrich
d' Arrest found Neptune near the predicted location.
Actually the planet was seen two hundred years earlier
by Galileo. He drew it's position but with his small
telescope, he did not recognize it as a planet.
Thirteen as of 7/23/06. Two were discovered pre-voyager, the other six by
voyager II. It's largest moon Triton is peculiar in that it's
orbit is retrograde. There is no definite explanation for why
it orbits in an opposite direction from other solar system
objects. Some theorized it is a captured moon and not part
of neptune's formation. Triton may actually be quite like
Pluto and it's moon Charon. It may have wandered too close
to Neptune and was captured by it's gravity. Triton also
had nitrogen geysers on it's surface. Some seemed to be
erupting when Voyager passed by.
Neptune possesses rings like the other Gas Giants. Before
Voyager arrived they were detected on Earth by the
same method as Uranus (occultation of a star). The rings
seemed to be incomplete though, they seemed like 'ring arcs'.
The mystery was solved by Voyager II. It seems the rings are
complete but have certain areas of greater concentration
of ring material. This is caused by moons whose gravity
causes concentration of ring material in certain segments.
OBSERVING - NAKED EYE
I am not aware of a naked eye observation. It may be possible
from a mountaintop under extremely dark skies. If you don't
have such an observing site, don't bother.
OBSERVING - TELESCOPE
A small telescope will show it's small blue disk. Any more
than that is extremely difficult. It may be possible to see
spots and bands as this has occasionally been reported
with larger amateur telescopes under good conditions.
Another observation to try with a moderate sized scope
is to spot the moon Triton. This is an easier observation
than any detail on Neptune.
A view of Neptune from it's moon Triton. The great dark spot and rings are
visible. The computer animation is 6 days, the orbital period of Triton.
The disk of Neptune from Triton would appear about 16 times the diameter
of our moon in the sky.
Neptune's clouds from Voyager including the 'Great Dark Spot'.
A closeup from Voyager of Neptune's moon Triton.
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