display the date on both planets according to Levitt's calendar and epoch (the Julian day epoch of 4713 BCE). Charles F. Capen included references to Mars dates in a 1966 Jet Propulsion Laboratory technical report associated with the Mariner 4 flyby of Mars. This system stretches the Gregorian calendar to fit the longer Martian year, much as Lowell had done in 1895, the difference being that 20 March, 21 June, 22 September, and 21 December marks the northward equinox, northern solstice, southward equinox, southern solstice, respectively. Similarly, Conway B. Leovy et al. also expressed time in terms of Mars dates in a 1973 paper describing results from the Mariner 9 Mars orbiter. British astronomer Sir Patrick Moore described a Martian calendar of his own design in 1977. His idea was to divide up a Martian year into 18 months. Months 6, 12 and 18, have 38 sols, while the rest of the months contain 37 sols. American aerospace engineer and political scientist Thomas Gangale first published regarding the Darian calendar in 1986, with additional details published in 1998 and 2006. It has 24 months to accommodate the longer Martian year while keeping the notion of a "month" that is reasonably similar to the length of an Earth month. On Mars, a "month" would have no relation to the orbital period of any moon of Mars, since Phobos and Deimos orbit in about 7 hours and 30 hours respectively. However, Earth and Moon would generally be visible to the naked eye when they were above the horizon at night, and the time it takes for the Moon to move from maximum separation in one direction to the other and back as seen from Mars is close to a Lunar month. Czech astronomer Josef Šurán offered a Martian calendar design in 1997, in which a common year has 672 Martian days distributed into 24 months of 28 days (or 4 weeks of 7 days each); in skip years, the week at the end of the twelfth month is omitted. Moore's 37-sol period 37 sols is the smallest integer number of sols after which the Mars Sol Date and the Julian date become offset by a full day. Alternatively, it can be viewed as the smallest integer number of sols needed for any Martian time zones to complete a full lap around Earth time zones. Specifically, 37 sols are equal to 38 Earth