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Western Slope Skies - Occultations have nothing to do with witchcraft


You may have heard the word “occult.” While the word often refers to a secret group that practices witchcraft or magical arts, the broader definition is “anything that is hidden.” In fact, the word “occult” has its roots in the Latin occultus, meaning “hidden, secret.” The same term applies when one object in the night sky goes behind another object and, hence, is hidden. A common occultation occurs when a star or planet is hidden as it passes behind the moon. Can you think of another type? We’ll discuss one in a moment.

Occultations can provide scientific data that are useful for many purposes. The primary scientific organization is International Occultation and Timing Association (IOTA). For example, when the moon occults a star, we can calculate the diameter of the moon by capturing rapid video frames and inserting the time on the frame. In a similar fashion, you can calculate the profile of an asteroid by using observations and timings from multiple locations on earth.

VERY accurate timing is needed for this. IOTA has specific requirements on the equipment.

Another example of occultations providing scientific value is the discovery of rings around Uranus in 1977, when the planet occulted a star. NASA noted the starlight winking off and on BEFORE it actually passed behind the planet and again as it re-appeared on the other side. Since then, the rings of Uranus have been imaged directly and detected through additional occultations.

Eclipses are another type of occultation. During a solar eclipse, the sun is hidden or partially hidden by the moon. A lunar eclipse is, technically, not an occultation as seen from Earth, although it is often referred to as an occultation. If the observer was on the moon, then they would see Earth occult the sun! Such an event would last much longer than a solar eclipse observed from Earth, because the Earth is much larger than the moon.

Note that the position of the observer is a key factor. Space.com discusses occultation events that can occur from the perspective of a satellite or even an Apollo spacecraft returning home. Other more esoteric occultation types are discussed as well.

Even if you are not interested in conducting serious occultation research, you can still enjoy observing a star or planet disappear or even capturing an image! The image on the KVNF website is a simulation of the occultation of the double star Zubenelgenubi by the moon on the morning of Feb 22, 2022. You can find predictions of various occultations at this IOTA link.


Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Bryan Cashion.

Links of Interest:
NASA lesson on occultations

Occultation of Saturn by the moon

Occultation of Mars by the moon

Video of an occultation of the star 67 Tauri by the moon on Feb. 9th, 2022, shot by Bryan Cashion.

Bryan Cashion
The moon occults 67 Tauri, Feb 9th, 2022