[Click to poseidonate.] These four images show Neptune using blue, red, and near-infrared filters. The atmosphere of the planet is laced with methane, which strongly absorbs red light and makes Neptune appear very blue to the eye. I've seen it through a telescope and the color is striking; I was using a 25 cm telescope at the time and the planet was just barely resolved as a disk. At 4.5 billion kilometers (3 billion miles) away, it's amazing even that was discernible!
In the big Hubble image above, the pink color is infrared light reflected from high-altitude clouds, and each image was taken four hours apart. In the smaller picture here (click to embiggen it), several of Neptune's moons can be seen, showing up as a series of dots as they moved between exposures. At the moment, 13 moons orbiting Neptune are known, ranging from the 2700-km-wide (1600 mile) Triton down to some smallish guys only 40 or so km across. There are undoubtedly more, but the planet is a long way off, and anything smaller than that is really hard to see. We've learned a huge amount about Neptune -- all the planets, of course! -- since it was discovered in 1846. With bigger telescopes, better detectors, and the ability to leave the bonds of Earth and loft telescopes above the atmosphere -- and even carry them on probes that go to the planets themselves, like Voyager 2 did when it flew past Neptune in 1989 -- our curiosity has only increased. And to think, we've only been studying Neptune for one year... Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)