Grazing lunar occultation explained

A grazing lunar occultation (also lunar grazing occultation, lunar graze, or just graze) is a lunar occultation in which as the occulted star disappears and reappears intermittently on the edge of the Moon.^[1] A team of many observers can combine grazes and reconstruct an accurate profile of the limb lunar terrain.

Since graze paths rarely pass over established observatories, amateur astronomers use portable observing equipment and travel to sites along the shadow path limits. The goal is to report the UTC of each event as accurately as possible, and GPS disciplined devices are frequently used as the time-base.Two methods are used to observe:

• visual – the observer has an audible UTC beeping device (e.g. a shortwave radio tuned to WWV) and an audio recorder (e.g. a tape recorder) and watches the target through the telescope, and calls 'Gone' when the star disappears, and 'Back' when the star reappears. The audio recording is later analysed to extract the event times.
• video – the observer uses a small video camera, usually mounted in the focuser of the telescope. A Video Time Inserter (VTI) is commonly used to insert a UTC time-stamp onto each frame of the recording. Either a camcorder, DVR or a laptop computer is used to record the video stream. The video recording is later analysed to extract event times.

Such observations are useful for:

• refining knowledge of the positions and motions of stars^[2]
• examining limb topographical profile around the lunar polar region.^[3]
• Measurement of the Earth's rotation^[4]

See also

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

References

1. Book: Buchheim, R. . The Sky is Your Laboratory: Advanced Astronomy Projects for Amateurs . Springer New York . Springer Praxis Books . 2007 . 978-0-387-73995-3 . 2021-10-08 . 40.
2. Examination of the Hipparcos Proper Motion System from Lunar Occultation Analysis. IAU Colloq. 180: Towards Models and Constants for Sub-Microarcsecond Astrometry. 115. Soma. Mitsuru. 2000tmcs.conf..115S. 2000.
3. Sôma. Mitsuru. Kato. Yuji. 2002-01-01. Limb profiles of the Moon from grazing occultation observations collected at RGO. National Astronomical Observatory of Japan. 6. 75–105. 2002PNAOJ...6...75S.
4. Stephenson. F. R.. Morrison. L. V.. Hohenkerk. C. Y.. 2016-12-01. Measurement of the Earth's rotation: 720 BC to AD 2015. Proc. R. Soc. A. en. 472. 2196. 20160404. 10.1098/rspa.2016.0404. 28119545. 1364-5021. 5247521. 2016RSPSA.47260404S.

Further reading

• Grazing Lunar Occultations, Royal Astronomical Society of New Zealand, https://web.archive.org/web/20041209112100/http://www.occsec.wellington.net.nz/graze/grazoccs.htm
• Eric. Limburg. 2002-01-10. Lunar Occultation Workbench 3.1: stellar occultations tailor-made to your needs. Occultation Newsletter, International Occultation Timing Association (IOTA) . en. 8. 4. 4. 0737-6766. 2002OccN....8d...4L. and
• Book: Wilds, Richard P. . Encyclopedia of Lunar Science . Lunar Occultations, Grazing . Springer International Publishing . Cham . 2018 . 1–10 . 10.1007/978-3-319-05546-6_220-3. 978-3-319-05546-6 .

External links

• Web site: Wood . Chuck . March 7, 2005 . One Good Occultation Deserves Another . Lunar Photo of the Day ., showing grazing occultation of Jupiter as seen from Melbourne, Australia
• Astronomy Picture of Day for March 16, 2007, showing grazing occultation of Saturn https://apod.nasa.gov/apod/ap070316.html
• International Occultation Timing Association Predicted paths for future grazing occultations
• Zodiacal Catalogue (XZ80Q) of stars that can be occulted by the moon http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=I/291/xz80q
• Web site: VizieR Lunar Occultation Archive. VizieR. Herald. David. vizier.u-strasbg.fr. 2018-06-16.
• Predictions and analysis of Lunar Occultations and Grazing Lunar Occultations. Occult (Software), Lunar Occultation Workbench (LOW) and GRAZEPREP