What is an occultation?

An occultation happens when one object passes in front of another from an observer's perspective. It is a term most often used in astronomy in reference to stellar, lunar, planetary and asteroid occultations. An example is a solar eclipse. From a certain area on Earth, the moon passes in front of the sun and either partially or totally blocks the light and so the sun is "eclipsed" or "occulted."

An asteroid occultation occurs when an asteroid passes in front of a star and by studying such occultations, for example through Saturn’s rings, astronomers have discovered hidden moons and moonlets. Similarly, planetary occultations have revealed a wealth of basic science about the planets in the solar system. An example is when scientists observed Uranus moving in front of a star in 1977 from the Kuiper Airborne Observatory. They found the Uranus planetary rings because they noticed the starlight winking on and off as the star first appeared to move toward the planet, and then again as the star moved away from the planet.

A practical example of occultation is to watch a car drive by at night where the headlights go past a picket fence. The headlights would blink on and off. With the right instrumentation in place one would be able to tell how many pickets there were and how wide they were.