Transit of Earth from Mars
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A transit of Earth across the Sun as seen from Mars takes place when the planet Earth passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars. During a transit, Earth can be seen from Mars as a small black disc moving across the face of the Sun.
The event is particularly interesting because both the Earth and the Moon can often be seen together in transit; however, sometimes one finishes transiting before the other begins (this last occurred in the 1800 transit, and will happen again in 2394).
No one has ever seen a transit of Earth from Mars, but the next one will take place on November 10, 2084, and could be observed by hypothetical future Mars colonists. The last such transit took place on May 11, 1984.
A 1971 science fiction short story by Arthur C. Clarke entitled Transit of Earth was about a doomed astronaut on Mars observing the 1984 transit; setting the story in 1984 turned out to be too optimistic. The short story was first published in the January 1971 issue of Playboy magazine.
Of course, observers on Mars can also see transits of Mercury and transits of Venus, as well as transits of Phobos and transits of Deimos.
Transits of Earth from Mars follow a 284-year cycle, occurring at intervals of 100.5, 79, 25.5, 79 years in either May or November. This cycle corresponds fairly closely to 151 Mars orbits, 284 Earth orbits, and 133 synodic periods, and is analogous to the cycle of transits of Venus from Earth, which follow a cycle of 243 years (121.5, 8, 105.5, 8).
A transit of Earth from Mars corresponds to Mars being perfectly uniformly illuminated at opposition from Earth, its phase being 180.0° without any defect of illumination. This permitted Charles Augustus Young to attempt a careful measurement of the oblateness (polar compression) of Mars during the 1879 event. He obtained the value 1/219, or 0.0046. This is close to the modern value of 1/154 (many sources will cite somewhat different values, such as 1/193, because even a difference of only a couple of kilometers in the values of Mars' polar and equatorial radii gives a considerably different result).
| November 10, 1595 | [1] |
| May 5, 1621 | [2] |
| May 8, 1700 | [3] |
| November 8, 1800 | [4] |
| November 12, 1879 | [5] |
| May 8, 1905 | [6] |
| May 11, 1984 | [7] |
| November 10, 2084 | [8] |
| November 15, 2163 | [9] |
| May 10, 2189 | [10] |
| May 13, 2268 | [11] |
| November 13, 2368 | [12] |
| May 10, 2394 | [13] |
| November 17, 2447 | [14] |
| May 13, 2473 | [15] |
[edit] See also
| Transit visibility from planets superior to the transiting body | ||||||
|---|---|---|---|---|---|---|
| Venus | Earth | Mars | Jupiter | Saturn | Uranus | Neptune |
| Mercury | Mercury | Mercury | Mercury | Mercury | Mercury | Mercury |
| Venus | Venus | Venus | Venus | Venus | Venus | |
| Earth | Earth | Earth | Earth | Earth | ||
| Mars | Mars | Mars | Mars | |||
| Jupiter | Jupiter | Jupiter | ||||
| Saturn | Saturn | |||||
| Uranus | ||||||
[edit] References
- Albert Marth, Note on the Transit of the Earth and Moon across the Sun’s Disk as seen from Mars on November 12, 1879, and on some kindred Phenomena, Monthly Notices of the Royal Astronomical Society, 39 (1879), 513–514. [16]
- Andrew Crommelin, Observations of Mars, 1904–6, Monthly Notices of the Royal Astronomical Society, 64 (1904), 520–521 [17]
- Jean Meeus & Edwin Goffin, Transits of Earth as Seen from Mars, Journal of the British Astronomical Association, 93 (1983), 120–123 [18]
- Charles Augustus Young, Measures of the Polar and Equatoreal Diameters of Mars, made at Princeton, New Jersey, U.S., The Observatory, 3 (1880), 471 [19]
