Editing Transit of minor planets

{{more footnotes|date=March 2012}}

A '''transit of a minor planet''' takes place when a [[minor planet]] passes directly between an observer and another heavenly body, obscuring a small part of that body's disc. From the perspective of observers on [[Earth]], transits of the [[Sun]] and [[Moon]] by minor planets are very rare, as the minor planets orbiting between the Earth and those bodies are few and very small. Transits of the Sun would be more visible from the [[outer planets]].

Transits should be distinguished from [[occultation]]s, in which the minor planet entirely blocks out the light from the other body.

==Asteroids==
Most asteroids orbit in the [[asteroid belt]] between [[Mars]] and [[Jupiter]]. For this reason, transits of the Sun by asteroids are rare from Earth's perspective, but would not be uncommon from the perspective of Jupiter. Still, the high [[inclination]] of many asteroid orbits would make this less common that it would be otherwise.  One example of a forthcoming asteroid transit visible from Jupiter will be that of [[4 Vesta]], which will transits the Sun on January 4, 2044, with an angular diameter of 0.24″.

From the perspective of Earth, the only types of asteroids that can transit the Sun are those with orbits that take them between the two bodies. These include [[Aten asteroid]]s (including [[Apohele asteroid]]s and the hypothetical [[Vulcanoid asteroid]]s) and some [[Apollo asteroid]]s (perhaps including [[quasi-satellite]]s of Earth). Unfortunately, observations of such transits are difficult because all of these asteroids are only a few kilometres in diameter at most, so that their [[angular diameter]] is too tiny to observe against the Sun.

One example was the May 16, 1990 transit of [[3838 Epona]] with a diameter of 2.5&nbsp;km.  At a distance of {{cvt|0.53|AU|km|lk=in}} from Earth, its angular diameter was only 0.007 seconds of arc, far too small to see. Similarly, asteroid [[30825 (1990 TG1)|30825 (1990 TG<sub>1</sub>)]] transited on April 14, 2005, but was again unobservable, having an angular diameter of about 0.05[[arc second|″]], and [[2101 Adonis]] transited on September 24, 2007, with an even smaller angular diameter of only 0.005″.

In theory, if a transit took place during a very close approach by a [[near-Earth asteroid]], it might be observable. However, no such asteroid transits have been observed up to the present time.

==Comets==
Comets may also transit the Sun; for example, [[Comet Halley|Halley's Comet]] transited on 19 May 1910.

Another example was [[C/1819 N1]], the Great Comet of 1819, but occurrence of that transit was not known until after it had happened, when the orbit was calculated, and although some observers later claimed to have seen the comet transiting the Sun at the time, these observations seem dubious.<ref>{{cite journal|title=On the Transit across the Sun's Disk of the Second or Great Comet of 1819|last1=Hind|first1=J. R.|author-link1=John Russell Hind|journal=Monthly Notices of the Royal Astronomical Society |year=1876|url=https://books.google.com/books?id=GC9DAQAAMAAJ&pg=PA309|volume=XXXVI|issue=7 |pages=309–313|doi=10.1093/mnras/36.7.309|bibcode = 1876MNRAS..36..309H |doi-access=free}}</ref>

==Transits of the moon==
It is theoretically possible that minor planets on an [[Earth-crossing]] orbit could transit the [[Moon]]. However, such events would be extremely rare since [[List of notable asteroids#Record-setting close approaches to Earth|only a few catalogued minor planets]], such as [[2004 FH]], have come closer to Earth than the distance of the Moon. Such an event might be observable (an asteroid of 25 metres' diameter at a distance of 380,000&nbsp;km has an angular diameter of 0.01″), but none has been observed as yet, although there have been some reports of such events, sometimes classified as [[UFO]]-sightings.

==See also==
* [[Transit of Mercury]]
* [[Transit of Venus]]
* [[Great Comet of 1819]]

==References==
{{reflist}}
 
* Martin Hoffmann, ''Asteroid transits over the disk of the Sun'', Minor Planet Bulletin '''16''' (1989), 16 [http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1989MPBu...16...11H] (1989MPBu...16...11H)

==External links==
* [http://ssd.jpl.nasa.gov/?horizons  JPL Horizons] (useful for calculating positions of solar system objects)
* [http://www.skywatchersindia.com/ TRANSIT OF VENUS 2012: Live Webcast(Multipoint)- by SWAN-India]
{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}

{{DEFAULTSORT:Transit Of Minor Planets}}
[[Category:Astronomical transits]]