Sciency Words: Occultation

Today’s post is part of a special series that first appeared on Planet Pailly. Every week, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s sciency word is:


You know that thing when the Moon passes in front of the Sun, completely blocking the Sun from our view here on Earth. That specific event, known as a solar eclipse, is an example of a more general phenomenon called an occultation.

The term is related to the more vernacular word “occult” in the sense that they both refer to things that are hidden. When a planet, moon, or other celestial body passes in front of a distant star, for example, the star is “occulted” in the sense that it is briefly hidden from sight.

Occultations are a rare and wonderful cosmic coincidence, and they also provide astronomers with an incredible opportunity. Whenever an occultation is predicted to occur, a great many powerful telescopes all across the globe swivel around to watch.

And sometimes amazing discoveries are made.

In 1977, the planet Uranus occulted a star with the unimaginative name of SAO 158687. After setting up their telescopes, astronomers presumably got their popcorn ready and waited to see what would happen. They were hoping some of the occulted starlight would pass through Uranus’s atmosphere, revealing the atmosphere’s structure and chemical composition.

Surprisingly, the show started early and ended late. SAO 158687 dimmed exactly five times before the occultation and exactly five times afterward. This provided the first evidence that Uranus has rings. At least five of them (we now know of thirteen Uranian rings).

And it’s a good thing we discovered those rings too. Given Uranus’s otherwise bland appearance, how else could I depict the planet’s sideways orientation without the help of those sideways oriented rings?


Written by James Pailly.

To read all the articles in the ‘Sciency Words‘ series, visit the Planet Pailly blog.

  • Paulo R. Mendes

    Fascinating. And Uranus saying “I’m sure you’d think of something” is hilarious! 😀