Grazing lunar occultation: Difference between revisions

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{{distinguish|text=a [[lunar eclipse]]}}
{{distinguish|text=a [[lunar eclipse]]}}
__NOTOC__
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[[File:OccultGrazeProfile-Observed.jpg|thumb|Figure 2: Observed events plotted on the limb topographical profile. It shows a plot of the results from a single observer graze expedition, where eight events were observed. The path of the star is shown curved, when in reality it is the moon moving past the star. The first disappearance is shown on the left (red) and the last reappearance on the right (green). The olive coloured dots are altitude soundings from the data points from the [[SELENE|Kaguya lunar orbiter]].]]


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]].<ref name="Buchheim 2007 p. 40">{{cite book | last=Buchheim | first=R. | title=The Sky is Your Laboratory: Advanced Astronomy Projects for Amateurs | publisher=Springer New York | series=Springer Praxis Books | year=2007 | isbn=978-0-387-73995-3 | url=https://books.google.com.br/books?id=JARaN7Jmm9cC&pg=PA40 | access-date=2021-10-08 | page=40}}</ref>
[[File:OccultLunarWorldMap.jpg|thumb|Figure 1: A map showing the path of the lunar shadow as it crosses the earth. In this case, the star is Antares and the predicted date is 2027 September 7th.]]
A team of many observers can combine grazes and reconstruct an accurate profile of the limb [[lunar terrain]].


⚫
[[File:OccultLunarWorldMap.jpg|thumb|Figure 1: A map showing the path of the lunar shadow as it crosses the earth. In this case, the star is Antares and the predicted date is 2027 September 7th. The left (western) ellipse represents moonrise for that region of the globe. The right (eastern) ellipse represents moon set for that region. The northern and southern path limits are shown. In the example shown, weather conditions allowing, sites between the white lines will see the event at night; sites between the blue lines will see the event during twilight; and sites between the red dotted lines during the day-time for stars brighter than (of a number lower than) second magnitude (<+2 Apparent Magnitude).<ref>Source – Occult (Software).</ref>]]
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]]). Light from the occulted object is blocked by the moon and a perceptible shadow of the moon is cast onto the ground if that ground is in night-time (facing away from the sun). The moon's shadow moves west-to-east due to the orbit of the moon and the rotation of the earth, as shown on Figure 1.


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Since graze paths rarely pass over established [[astronomical observatory|observatories]], [[amateur astronomer]]s use portable observing equipment and travel to sites along the shadow path limits. The goal is to report the [[Coordinated Universal Time|UTC]] of each event as accurately as possible, and [[Global Positioning System|GPS]] disciplined devices are frequently used as the time-base.
⚫
The left (western) ellipse represents moonrise for that region of the globe. The right (eastern) ellipse represents moon set for that region. The northern and southern path limits are shown. In the example shown, weather conditions allowing, sites between the white lines will see the event at night; sites between the blue lines will see the event during twilight; and sites between the red dotted lines during the day-time for stars brighter than (of a number lower than) second magnitude (<+2 Apparent Magnitude).<ref>Source – Occult (Software).</ref>

A '''grazing lunar occultation''' (also '''lunar grazing occultation''', '''lunar graze''', or just '''graze''') is seen at locations along the north and south limits, and the observer will see the object disappear as the shadow of mountains pass by, and reappear as the light passes down the valleys on the edge of the moon.

[[File:OccultGrazeProfile-Observed.jpg|thumb|Figure 2: Observed events plotted on the limb topographical profile.]]

⚫
Figure 2 shows a plot of the results from a single observer graze expedition, where eight events were observed. The path of the star is shown curved, when in reality it is the moon moving past the star. The first disappearance is shown on the left (red) and the last reappearance on the right (green). The olive coloured dots are altitude soundings from the data points from the [[SELENE|Kaguya lunar orbiter]].

⚫
A team of many observers can combine observed events and construct an accurate profile of the [[lunar terrain]]. Since graze paths rarely pass over established [[astronomical observatory|observatories]], [[amateur astronomer]]s use portable observing equipment and travel to sites along the shadow path limits. The goal is to report the [[Coordinated Universal Time|UTC]] of each event as accurately as possible, and [[Global Positioning System|GPS]] disciplined devices are frequently used as the time-base.
Two methods are used to observe:
Two methods are used to observe:
* visual – the observer has an audible UTC beeping device (e.g. a shortwave radio tuned to [[WWV (radio station)|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.
* visual – the observer has an audible UTC beeping device (e.g. a shortwave radio tuned to [[WWV (radio station)|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]], [[Digital video recorder|DVR]] or a [[laptop]] computer is used to record the video stream. The video recording is later analysed to extract 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]], [[Digital video recorder|DVR]] or a [[laptop]] computer is used to record the video stream. The video recording is later analysed to extract event times.

⚫
All known lunar occultations, (both total lunar occultations as well as grazing lunar occultations) are archived at the [[VizieR]] service.<ref>{{Cite web|url=http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=VI/132B|title=VizieR Lunar Occultation Archive|last=Herald|first=David|website=vizier.u-strasbg.fr|access-date=2018-06-16}}</ref>


Such observations are useful for:
Such observations are useful for:
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== See also==
== See also==

* [[Asteroid occultation]]
* [[Asteroid occultation]]
* [[Occultation]]
* [[Occultation]]
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*Grazing Lunar Occultations, [[Royal Astronomical Society of New Zealand]], [https://web.archive.org/web/20041209112100/http://www.occsec.wellington.net.nz/graze/grazoccs.htm]
*Grazing Lunar Occultations, [[Royal Astronomical Society of New Zealand]], [https://web.archive.org/web/20041209112100/http://www.occsec.wellington.net.nz/graze/grazoccs.htm]
* {{Cite journal|last=Eric|first=Limburg|date=2002-01-10|title=Lunar Occultation Workbench 3.1: stellar occultations tailor-made to your needs|journal=Occultation Newsletter, International Occultation Timing Association (IOTA) |language=en|volume=8|issue=4|pages=4|issn=0737-6766|bibcode=2002OccN....8d...4L}}</ref> and
* {{Cite journal|last=Eric|first=Limburg|date=2002-01-10|title=Lunar Occultation Workbench 3.1: stellar occultations tailor-made to your needs|journal=Occultation Newsletter, International Occultation Timing Association (IOTA) |language=en|volume=8|issue=4|pages=4|issn=0737-6766|bibcode=2002OccN....8d...4L}}</ref> and
* {{cite book | last=Wilds | first=Richard P. | title=Encyclopedia of Lunar Science | chapter=Lunar Occultations, Grazing | publisher=Springer International Publishing | publication-place=Cham | year=2018 | doi=10.1007/978-3-319-05546-6_220-3}}


==External links==
==External links==
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*Astronomy Picture of Day for March 16, 2007, showing grazing occultation of Saturn [https://apod.nasa.gov/apod/ap070316.html]
*Astronomy Picture of Day for March 16, 2007, showing grazing occultation of Saturn [https://apod.nasa.gov/apod/ap070316.html]
*[http://www.lunar-occultations.com/iota/iotandx.htm International Occultation Timing Association] Predicted paths for future grazing occultations
*[http://www.lunar-occultations.com/iota/iotandx.htm 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]
* 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]
⚫
* {{Cite web|url=http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=VI/132B|title=VizieR Lunar Occultation Archive|publisher=[[VizieR]]|last=Herald|first=David|website=vizier.u-strasbg.fr|access-date=2018-06-16}}
*Predictions and analysis of Lunar Occultations and Grazing Lunar Occultations. Occult (Software), Lunar Occultation Workbench (LOW) and [http://www.iota-es.de/moon/lunar_grazings.html GRAZEPREP]
*Predictions and analysis of Lunar Occultations and Grazing Lunar Occultations. Occult (Software), Lunar Occultation Workbench (LOW) and [http://www.iota-es.de/moon/lunar_grazings.html GRAZEPREP]


Revision as of 23:39, 8 October 2021

Not to be confused with a lunar eclipse.
Figure 2: Observed events plotted on the limb topographical profile. It shows a plot of the results from a single observer graze expedition, where eight events were observed. The path of the star is shown curved, when in reality it is the moon moving past the star. The first disappearance is shown on the left (red) and the last reappearance on the right (green). The olive coloured dots are altitude soundings from the data points from the Kaguya lunar orbiter.

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.

Figure 1: A map showing the path of the lunar shadow as it crosses the earth. In this case, the star is Antares and the predicted date is 2027 September 7th. The left (western) ellipse represents moonrise for that region of the globe. The right (eastern) ellipse represents moon set for that region. The northern and southern path limits are shown. In the example shown, weather conditions allowing, sites between the white lines will see the event at night; sites between the blue lines will see the event during twilight; and sites between the red dotted lines during the day-time for stars brighter than (of a number lower than) second magnitude (<+2 Apparent Magnitude).[2]

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[3]
  • examining limb topographical profile around the lunar polar region.[4]
  • Measurement of the Earth's rotation[5]

See also

References

  1. ^ Buchheim, R. (2007). The Sky is Your Laboratory: Advanced Astronomy Projects for Amateurs. Springer Praxis Books. Springer New York. p. 40. ISBN 978-0-387-73995-3. Retrieved 2021-10-08.
  2. ^ Source – Occult (Software).
  3. ^ Soma, Mitsuru (2000). "Examination of the Hipparcos Proper Motion System from Lunar Occultation Analysis". IAU Colloq. 180: Towards Models and Constants for Sub-Microarcsecond Astrometry: 115. Bibcode:2000tmcs.conf..115S.
  4. ^ Sôma, Mitsuru; Kato, Yuji (2002-01-01). Limb profiles of the Moon from grazing occultation observations collected at RGO (PDF) (Report). National Astronomical Observatory of Japan. Vol. 6. pp. 75–105. Bibcode:2002PNAOJ...6...75S.
  5. ^ 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. 472 (2196): 20160404. Bibcode:2016RSPSA.47260404S. doi:10.1098/rspa.2016.0404. ISSN 1364-5021. PMC 5247521. PMID 28119545.

Further reading

External links

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