The Neptune System
Before 1975, Uranus and Neptune were thought to be very similar to each other. After all, they are gaseous planets and have similar sizes, masses and colors. The problem with this thinking, though, was that we did not know much about either planet. We had little information on their meteorology, atmospheric composition and clouds. This began to change in 1976, when astronomers discovered that Neptune brightened by at least a factor of four in near-infrared (near-IR) light; furthermore, this brightness changed over several hours due to its rotation. This rise and fall in brightness was the first hint that things were different on Neptune. Over the next 30 years, our knowledge of Neptune has increased to the point where a more informed discussion of it can be presented.