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Deimos transits the Sun, as seen by Mars Rover Opportunity on March 4, 2004

A transit of Deimos across the Sun as seen from Mars takes place 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, Deimos can be seen from Mars as a small black disc rapidly moving across the face of the Sun.

The event could also be referred to as a partial occultation (or, popularly but inaccurately, a partial eclipse) of the Sun by Deimos. However, since the angular diameter 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 2 1/2 times the angular diameter of Venus as seen from Earth during a transit of Venus from Earth.

A transit of Deimos from Mars lasts a maximum of about two minutes, due to its relatively rapid orbital period 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, zero or one transits of Deimos can be seen by observers at that geographical location (compared to about half a dozen transits of Phobos).

It is easy to see that the shadow always falls on the "winter hemisphere", except when it crosses the equator during the vernal equinox and the autumnal equinox. Thus transits of Deimos happen during Martian autumn and winter in the northern hemisphere and the southern hemisphere, roughly symmetrically around the winter solstice. Close to the equator they happen around the autumnal equinox and the vernal equinox; 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 March 4, 2004 a transit was photographed by Mars Rover Opportunity, while on March 13, 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.


March 4, 2004 transit from Opportunity
Deimos Mar 04 2004 from Opportunity 1.jpg Deimos Mar 04 2004 from Opportunity 2.jpg Deimos Mar 04 2004 from Opportunity 3.jpg Deimos Mar 04 2004 from Opportunity 4.jpg
03:03:43
10:28:17
03:03:53
10:28:27
03:04:03
10:28:36
03:04:13
10:28:46
March 13, 2004 transit from Spirit
Deimos Mar 13 2004 from Spirit 1.jpg Deimos Mar 13 2004 from Spirit 2.jpg Deimos Mar 13 2004 from Spirit 3.jpg Deimos Mar 13 2004 from Spirit 4.jpg Deimos Mar 13 2004 from Spirit 5.jpg Deimos Mar 13 2004 from Spirit 6.jpg Deimos Mar 13 2004 from Spirit 7.jpg Deimos Mar 13 2004 from Spirit 8.jpg
00:04:27
13:54:11
00:04:37
13:54:20
00:04:47
13:54:30
00:04:57
13:54:40
00:05:07
13:54:50
00:05:17
13:54:59
00:05:27
13:55:09
00:05:37
13:55:19
March 9, 2005 transit from Spirit
Deimos Mar 09 2005 from Spirit 01.jpg Deimos Mar 09 2005 from Spirit 02.jpg Deimos Mar 09 2005 from Spirit 03.jpg Deimos Mar 09 2005 from Spirit 04.jpg Deimos Mar 09 2005 from Spirit 05.jpg Deimos Mar 09 2005 from Spirit 06.jpg Deimos Mar 09 2005 from Spirit 07.jpg Deimos Mar 09 2005 from Spirit 08.jpg Deimos Mar 09 2005 from Spirit 09.jpg Deimos Mar 09 2005 from Spirit 10.jpg Deimos Mar 09 2005 from Spirit 11.jpg
15:58:19 15:58:29 15:58:39 15:58:49 15:58:59 15:59:09 15:59:19 15:59:29 15:59:39 15:59:49 15:59:59

The data in the tables below is generated using 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).

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.

Transits of Deimos from Mars Rover Spirit landing site
Duration
Earth time (UTC)
Duration
(Local Solar time)
Minim.
separ.
Deimos
ang. diam.
Sun
ang. diam.
Sun
alt.
April 24, 2003
03:05:36
10 12 59 888.8" 151.0" 1296.4" 58.3°
April 25, 2003
(10:22:29 – 10:24:25)
16 39 46 – 16 41 39 248.4" 139.6" 1297.8" 18.5°
March 13, 2004
(00:05:06 – 00:06:35)
13 56 12 – 13 57 39 458.6" 150.6" 1225.0" 56.8°
March 9, 2005
(15:54:16 – 15:56:14)
14 49 07 – 14 51 02 261.4" 147.6" 1294.5" 44.3°
January 26, 2006
05:28:45
11 57 05 1509.5" 153.4" 1227.9" 74.0°
January 22, 2007
21:19:39
12 52 10 982.8" 152.6" 1291.6" 67.8°
December 12, 2007
18:10:49
16 26 33 850.0" 140.9" 1229.2" 22.3°
Transits of Deimos from Mars Rover Opportunity landing site
Duration
Earth time (UTC)
Duration
(Local Solar time)
Minim.
separ.
Deimos
ang. diam.
Sun
ang. diam.
Sun
alt.
May 30, 2003
(00:06:57 – 00:09:04)
13 28 59 – 13 31 02 95.8" 152.5" 1306.3" 67.3°
March 4, 2004
(03:03:52 – 03:05:06)
10 30 14 – 10 31 25 550.0" 152.6" 1233.6" 67.6°
March 5, 2004
10:21:52
16 58 21 1041.5" 138.6" 1232.3" 15.4°
March 17, 2005
05:28:44
11 28 40 1041.8" 154.0" 1303.0" 81.6°
March 18, 2005
(12:36:42 – 12:38:43)
17 46 46 – 17 48 43 89.6" 134.3" 1304.4" 3.0°
January 18, 2006
(15:54:26 – 15:56:21)
15 08 00 – 15 09 52 198.4" 147.2" 1235.3" 42.7°
January 31, 2007
18:15:01
16 02 28 824.8" 143.2" 1301.4" 29.3°
December 3, 2007
21:20:36
13 11 25 739.0" 153.1" 1238.0" 72.1°

See also

References

  • J. Bell, M. Lemmon, M. Wolff, Transits of Mars I and II, IAU Circ., 8298, 2 (2004). [1] (TeX DVI file is at [2]).

External links

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