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Space (i.e., in this book) does not permit an exploration of the topics of nanotechnology, utilization of planetary and asteroidal resources, terraforming, and related topics. The interested reader should consult the bibliography and read some of the many excellent references in these areas. |
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In many respects relevant to calendars, Mars resembles Earth very closely. Earth and Mars rotate on their respective axes in amounts of time that are surprisingly close. The sidereal day for Earth is 23.935 hours, and that of Mars is 24.623 hours. Thus, the Martian day is only about 39 minutes longer than a Terran day. |
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The angle of inclination of equator to orbital plane of both planets is also remarkably similar. Mars is inclined in its orbit at 25 degrees, compared to Earth's 23.5 degrees. This means that Mars experiences seasons, much in the Terran fashion. |
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Mars also differs from Earth in certain significant ways. Certainly, its mass, gravity, temperature, and so on are different. More importantly for our concerns, the orbit of Mars is somewhat more eccentric (0.093) than that of Earth (0.0167). This fact has certain consequences. First, Mars at perihelion is about 206.66 million kilometers from the Sun, but is 249.22 million kilometers at aphelion, or some 43 million kilometers further away. The ratio of the amounts of solar radiation received at these two locations is inversely proportional to the square of the ratio of the two distances. Hence, 1/(206.66/249.22)2 = 1.45, so Mars receives about 45% more sunlight at perihelion than at aphelion. Hence, Mars is distinctly hotter at perihelion. |
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Second, since planets move faster in their orbits at perihelion, the further consequence is that seasons are of unequal duration in the Martian northern and southern hemispheres. |
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The durations of sidereal days are given in Table 9.36. |
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Perihelion occurs late in the southern spring, so southern spring and summer experience substantially higher temperatures than northern spring and summer. |
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| Table 9.36 Durations of Martian seasons in sidereal days. | Northern
Hemisphere | Southern
Hemisphere | Terran
Days | Martian
Days | Northern
Winter=1 | | Spring | Autumn | 199.2 | 194.2 | 1.25 | | Summer | Winter | 181.4 | 176.8 | 1.13 | | Autumn | Spring | 145.5 | 141.8 | 0.91 | | Winter | Summer | 159.9 | 155.8 | 1.00 |
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