Scientists Say: Occultation

1 day ago 2

Occultation (noun, “uh-kuhl-TAY-shion”)

An occultation is when one celestial object passes in front of another that looks smaller in the sky. For instance, the moon or an asteroid might block the light from a distant star.

Occultations occur pretty much every night. As the moon wanders across the night sky, it passes in front of stars and planets. These are called lunar occultations.

Less common are planetary occultations. This is when a planet blocks a distant object from view. These events give astronomers a chance to learn new things about the planet, such as features of its atmosphere.

Occultations sometimes lead to discoveries. In 1977, Uranus passed in front of a distant star. Astronomers noticed the star’s light dimmed five times before Uranus completely blocked it. The star also flickered five times after the occultation.

Astronomers realized that Uranus must have rings like Saturn. Uranus’s rings do not glow brightly like Saturn’s. That made them harder to detect. But each time the star dimmed, one of Uranus’s five rings was blocking its light.

Occultations have helped scientists learn about our moon, too. Watching how starlight flickers as it passes behind the moon can reveal mountains and valleys. Timing how long stars disappear behind asteroids can help scientists measure the sizes of these space rocks.

The word occultation is similar to two other terms in astronomy: eclipse and transit. When the moon passes in front of and blocks out the sun, for example, we get a total solar eclipse.

A transit happens when one smaller-looking object passes in front of a larger one. This is what happens when an exoplanet passes in front of the distant star it’s orbiting.