Deimos passage from Mars

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Deimos passage from Mars captured by the Mars Rover Opportunity on March 4, 2004

A passage of the Martian moon Deimos in front of the sun , as seen from Mars , occurs when Deimos passes directly between the sun and a point on the Martian surface. During such a transit, Deimos with a solar filter would be seen as a small black disk of somewhat irregular shape that moves quickly across the solar disk. Its shadow would hardly be visible from an orbit, because only the penumbra reaches Mars.

The event can be understood as a partial eclipse of the sun by Deimos. However, because the angular diameter of Deimos - seen from Mars - is only around 1/10 of the apparent diameter of the sun , the phenomenon is more likely to be described as a passage. The angular diameter of Deimos is only about 2½ times the angular diameter of Venus at one of the Earth observed Venus transit . In contrast to its duration of a few hours, a passage from Deimos on Mars only takes one to two minutes, because the small moon has a relatively short orbital period of 30.3 hours.

Because Deimos does not orbit Mars exactly in its equatorial plane - and this is inclined by 25.2 ° to the plane of the planet's orbit around the sun - the shadow of Deimos touches the Martian surface at different latitudes in the course of a Mars year . However, the moon's shadow passes the planet about ¾ of the Martian year.

For every areographic position on the Martian surface (excluding the polar regions) there are two points in time in the Martian year at which the shadow of Deimos moves over them. During this period the observer can see at most one Deimos transit (because of the small size of the moon) . The shadow always falls on the "winter hemisphere" unless it crosses the equator during the equinox . For example, Deimos transits during the fall of Mars and winter in the northern and southern hemisphere, roughly symmetrically around the winter solstice . Near the equator they happen around the equinoxes in spring and autumn; further away from the equator, they occur around the winter solstice.

The passages are only possible up to a width of about 82 °. Because Deimos orbits relatively close to Mars, he cannot be seen there more north than 82 ° or more south than −82 °.

literature

  • JF Bell et al. : Solar eclipses of Phobos and Deimos observed from the surface of Mars . In: Nature . tape 436 , 2005, pp. 55-57 , doi : 10.1038 / nature03437 .

Hints

  1. ↑ This results from the angle of 8.2 ° at which Mars appears from Phobos, and the inclination of the planet's axis from its orbital plane of over 25 ° (estimate by Geof , April 2017)

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Passages in our solar system
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
  moon Deimos     Saturn Saturn
    Phobos       Uranus