|Neptune. It's blue appearance is due to traces|
of methane in its atmosphere. The spots, like
the spots in Jupiter's atmosphere, indicate active
NASA Hubble Space Telescope photo.
Neptune is the farthest planet from the Sun, the fourth-largest planet by diameter, and has 17 times the mass of the Earth. It is about 30 times the distance from the sun as the earth. It was discovered on September 23, 1846 and was the first planet found because of a mathematical prediction. Alexis Bouvard, a French astronomer could not predict the orbit of Uranus accurately without invoking a gravitational perturbation by an unknown planet. It was subsequently observed by Johann Galle, and shortly after, it's largest moon, Triton, was discovered as well. (When Voyager 2 flew by Triton in 1989, its instruments detected erupting geysers on the surface, see reference below.) It has the strongest sustained winds of any planet in the solar system, a record of 2100 km/hour (583 m/s).
Why "Happy Birthday?" Neptune's "year" is 164.8 Earth years, so only now has Neptune returned to the same spot in its orbit as it had when it was discovered in September, 1846. Neptune has four seasons, like earth, but each season lasts about 41 Earth years.
References on Triton's geysers: