The Mars time of noon is 12:00 which is in Earth time 12 hours and 20 minutes after midnight.įor the Mars Pathfinder, Mars Exploration Rover (MER), Phoenix, and Mars Science Laboratory missions, the operations teams have worked on "Mars time", with a work schedule synchronized to the local time at the landing site on Mars, rather than the Earth day. This has the advantage that no handling of times greater 23:59 is needed, so standard tools can be used. Time of day Ī convention used by spacecraft lander projects to date has been to enumerate local solar time using a 24-hour "Mars clock" on which the hours, minutes and seconds are 2.75% longer than their standard (Earth) durations. Numerically, the Mars Sol Date is defined as MSD = (Julian Date using International Atomic Time - 2451549.5 + k)/1.02749125 + 44796.0, where k is a small correction of approximately 1⁄ 4000 d (or 21.6 s) due to uncertainty in the exact geographical position of the prime meridian at Airy-0 crater. This Mars Sol Date (MSD) starts "prior to the 1877 perihelic opposition." Thus, the MSD is a running count of sols since 29 December 1873 (coincidentally the birth date of astronomer Carl Otto Lampland). An analogous system for Mars has been proposed "or historical utility with respect to the Earth-based atmospheric, visual mapping, and polar-cap observations of Mars., a sequential count of sol-numbers". When accounting solar days on Earth, astronomers often use Julian dates-a simple sequential count of days-for timekeeping purposes. By inference, Mars' "solar hour" is 1⁄ 24 of a sol (1 hr 1 min 39 sec), and a "solar minute" 1⁄ 60 of a solar hour (61.65 sec) "solar second" 1⁄ 60 of a solar minute (1.0275 sec). The term was adopted during NASA's Viking project (1976) in order to avoid confusion with an Earth "day". The term " sol" is used by planetary scientists to refer to the duration of a solar day on Mars. The corresponding values for Earth are currently 23 h 56 m 4.0916 s and 24 h 00 m 00.002 s, respectively, which yields a conversion factor of 1.0 Earth days/sol: thus, Mars's solar day is only about 2.75% longer than Earth's.
That is a convenient organization of time for us.The average length of a Martian sidereal day is 24 h 37 m 22.663 s (88,642.663 seconds based on SI units), and the length of its solar day is 24 h 39 m 35.244 s (88,775.244 seconds). But if people go to Mars, they may have need for some monthly reckoning. “You couldn’t construct a practical reference to the orbits of the Mars moons for a convenient seasonal division.
“I have January, February, Bradbury, Clarke and March,” he said with a laugh. He wanted Mars months to follow Earth months in terms of things like equinoxes, so he stuck in extra months here and there. Northern winter starts when the sun is at 90 degrees, and so on.Īllison has tackled this, too, creating a Mars calendar with 10 extra months. The year begins when the sun stands directly above the Martian equator, moving north as viewed from Mars - the start of spring. Instead, scientists mark the calendar using the longitude of the sun. The Martian moons, Phobos and Deimos, careen around their planet so quickly that there’s no point dividing up the calendar according to their phases. Just as an aside, while we’re talking about organization of time, you can forget about Mars months or a Gregorian calendar. “I actually know Mars time, in a way, better than Earth time,” he jokes. Michael Allison, an emeritus professor at the Goddard Institute for Space Studies, has made a hobby of figuring it out. So engineers need a reliable method to keep track of time on the planet. Curiosity has a nuclear generator, but it will still be a solar craft in many ways - its cameras and other instruments need sunlight to see, and atmospheric phenomena, like the huge temperature shift between day and night on Mars, follows the movement of the sun. Most Mars missions have been solar-powered, meaning the spacecraft must do its work during daylight hours. Just as we mark our lives according to the passage of time, so too do space missions. It’s only a little bit, because an hour - who cares, that’s not so bad. “It feels like you are perpetually flying east 40 minutes every day,” said Deborah Bass, a scientist at JPL who worked on the Spirit and Opportunity rovers and the Phoenix lander.
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