A transit of Deimos across the Sun as seen from

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atm ...

occurs when Deimos passes directly between the Sun and a point on the surface of Mars, obscuring a small part of the Sun's disc for an observer on Mars. During a

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

, Deimos can be seen from Mars as a small dark spot rapidly moving across the Sun's face. The event could also be referred to as a partial

eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...

of the Sun by Deimos. However, since the

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it i ...

of Deimos is only about 1/10 of the angular diameter of the Sun as seen from Mars, it is more natural to refer to it as a transit. The angular diameter of Deimos is only 2½ times the angular diameter of

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

as seen from Earth during a

transit of Venus frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a trans ...

from Earth.

Transit

A transit of Deimos from Mars lasts a maximum of about two minutes, due to its relatively rapid

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, ...

of about 30.3 hours. Because they orbit Mars in low-inclination equatorial orbits, the shadows of Phobos or Deimos projected onto the surface of Mars exhibit a seasonal variation in latitude. At any given geographical location on the surface of Mars, there are two intervals in a Martian year when the shadows of Phobos or Deimos are passing through its latitude. During each such interval, no or one transit of Deimos can be seen by observers at that geographical location (compared to about half a dozen transits of Phobos). The shadow always falls on the "winter hemisphere", except when it crosses the equator during the

March March is the third month of the year in both the Julian and Gregorian calendars. It is the second of seven months to have a length of 31 days. In the Northern Hemisphere, the meteorological beginning of spring occurs on the first day of Ma ...

and September equinoxes. Thus transits of Deimos happen during Martian autumn and winter in the northern hemisphere and the southern hemisphere, roughly symmetrically around the

winter solstice The winter solstice, also called the hibernal solstice, occurs when either of Earth's poles reaches its maximum tilt away from the Sun. This happens twice yearly, once in each hemisphere ( Northern and Southern). For that hemisphere, the winte ...

. Close to the equator they happen around the March and September equinoxes; farther from the equator they happen closer to the winter solstice. Because it orbits relatively close to Mars, Deimos cannot be seen north of 82.7°N or south of 82.7°S; such latitudes will obviously not see transits either. On 4 March 2004, a transit was photographed by Mars Rover ''Opportunity'', while on 13 March 2004, a transit was photographed by Mars Rover '' Spirit''. In the captions below, the first row shows Earth time UTC and the second row shows Martian local solar time. The data in the tables below is generated usin
JPL Horizons
There is some discrepancy of a minute or two with the times reported for the series of images above. This may be due to imprecision in the ephemeris data used by JPL Horizons; also the JPL Horizons data gives local apparent solar time while the times reported above are probably some form of mean solar time (and therefore some of the discrepancy would be due to the Martian equivalent of the

equation of time In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in ...

). Note: the data below is valid for the original landing sites. To the extent that the rovers have moved around on the surface, the parameters of the transits as actually observed may be slightly different. Near misses are in italics.

Observation by InSight

A transit lightcurve of Deimos was obtained in 2020 using the solar array currents measured by the InSight lander. The light drop was about 0.9% (possibly less than the predicted geometric obstruction of 1% due to light scattering by atmospheric dust outside the shadow). The transit lasted between 116 and 124 seconds.

References

External links

JPL Horizons
(must use telnet interface for non-Earth observation points)

(small images of the 4 March 2004 transit are near the bottom of the page).

(small images of the 13 March 2004 transit are near the bottom of the page).

(small images of the 9 March 2005 transit are near the middle of the page).
Animation of 4 March 2004 transit
{{DEFAULTSORT:Transit Of Deimos From Mars Astronomical transits Deimos (moon)

Transit

Observation by InSight

See also

Further reading

References

External links