Explanation:
Neptune rotates
once on its axis in about 16 hours.
So, spaced about 4 hours apart
these 4 images
of the solar system's most distant gas giant
cover one Neptune day.
Recorded by the Hubble Space Telescope in late June they
combine exposures made with visible and near-infrared filters to
show high-altitude clouds composed of
methane ice crystals against
the planet's normally blue
cloud tops.
Because Neptune's axis of rotation is tilted to its orbital
plane by 29 degrees, compared to Earth's 23.5 degrees,
Neptune experiences
seasons analogous to Earth's.
As early summer comes to Neptune's
southern hemisphere and winter
to the north, Hubble observations have shown cloud activity shifting
to the northern hemisphere.
In fact the progression of Neptune's seasons has come around once since
its position
was predicted by French mathematician Urbain Le Verrier
and British mathematician
John Couch Adams,
and the planet was subsequently discovered
by German astronomer Johann Galle on September 23, 1846.
With an orbital period of approximately 165 years, this week on
July 12, Neptune
has been once around the Sun since its discovery date.
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