A lunar occultation occurs when the Moon, moving along its orbital path, passes in front of a star or other celestial object, as seen by an observer (normally on the Earth). A grazing lunar occultation (also lunar grazing occultation, lunar graze, or just graze) occurs when one of the two edges of the moon parallel to its orbital path appears to just touch or graze the object as the moon goes by. When this happens, a properly positioned observer will see the grazed object disappear and reappear, possibly several times, as mountains and valleys on the edge of the moon pass in front of it. In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ... Apparent magnitude: up to -12. ... This article is about the astronomical object. ...

Grazes unfold over the course of a few minutes, and depending on the lunar terrain and the observer’s position, the object may disappear and reappear just once or more than 10 times. Observers deployed just a few hundred yards apart on a line perpendicular to the graze path may make radically different observations. For example, at one location a mountain may pass in front of the object, causing it to disappear and reappear, while at a different position the mountain may simply pass below the star without obscuring it.

By carefully measuring the positions of many observers and timing the disappearance and reappearance events, it is possible to construct an extremely accurate profile of the lunar terrain. Since graze paths rarely pass over established observatories, amateur astronomers have become the primary recorders of graze data. They typically use portable GPS units to determine their positions and telescope mounted video cameras to record the disappearance and reappearance events. Accurate timing is provided by recording time signals from WWV on the audio channel. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... WWV is the callsign of NISTs shortwave radio station located in Fort Collins, Colorado. ...

See also

• Occultation
• Grazing occultation
• Asteroid occultation
• Transit (occultations of planets by other planets)

In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ... An occultation is an astronomical event that occurs when one celestial object is hidden by another celestial object that passes between it and the observer. ... An asteroid occultation occurs when an asteroid passes in front of a star (occults a star), temporarily blocking its light (as seen from Earth). ... 2003 Transit of Mercury The term transit or astronomical transit has two meanings in astronomy: A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point. ...

External links and references

• International Occultation Timing Association Predicted paths for future grazing occultations
• Royal Astronomical Society of New Zealand More extensive description of grazing occultations
• Astronomy Picture of Day for March 16, 2007, showing grazing occultation of Saturn