What Is Lunar Occultation?

Graze

• A lunar occultation takes place when the shadow of a star falls on the Earth and the moon blocks the shadow from reaching the Earth. An occultation is visible in a small zone, usually around 2 miles in width, that remains behind the moon for around one hour. Along with stars, a lunar occultation can take place when the moon passes in front of another celestial object, such as a major or minor planet.

Grazing

• A grazing lunar occultation occurs when a star or other celestial object passes behind the north or south pole of the moon. Grazing lunar occultations are characterized by the movement of celestial objects appearing and disappearing behind the craters and mountains found on the moon. The stars and planets that are hidden behind the moon pass behind the topography of the moon, allowing astronomers to research and record the topography of the moon's poles. By measuring the amount of time it takes for a star to pass behind a mountain of the moon's surface, the size and location of the mountain on the moon can be estimated.

Timing

• Lunar occultations are recorded by astronomers by recording a time code from an FM or AM radio station, or by using a high quality video recording with a time code. During the recording, the astronomer records the appearances and disappearances of the star behind the moon; appearances are recorded as A and disappearances are D. The timings of the lunar occultations are used by astronomers to map the location and size of the stars and planets in space. To gain exact measurements and timings, the exact location of the telescope should be recorded in relation to nearby landmarks to within a distance of 10 feet.

Importance

• Astronomers find lunar occultations important to record and research as they can assist in the prediction of the location of solar eclipses. Other reasons to record and time occultations are the movement of the stars in space and the rotation of the Milky Way galaxy in relation to other celestial objects. The tilt of the Earth on its axis can also be calculated in relation to the orbit of the Earth around the sun.