Astronomy on Mars

The seasonal lag on Mars is no more than a couple of days,[1] due to its lack of large bodies of water and similar factors that would provide a buffering effect.

Thus, for temperatures on Mars, "spring" is approximately the mirror image of "summer" and "autumn" is approximately the mirror image of "winter" (if the solstices and equinoxes are defined to be the beginnings of their respective seasons), and if Mars had a circular orbit the maximum and minimum temperatures would occur a couple of days after the summer and winter solstices, rather than about one month after, as on Earth.

Aside from the eccentricity, the Earth's axial tilt can also vary from 21.5° to 24.5°, and the length of this "obliquity cycle" is 41,000 years.

These and other similar cyclical changes are thought to be responsible for ice ages (see Milankovitch cycles).

The normal hue of the sky during the daytime can vary from a pinkish-red to a yellow-brown “butterscotch” color; however, in the vicinity of the setting or rising sun it is blue.

It is believed that the color of the sky is caused by the presence of 1% by volume of magnetite in the dust particles.

Twilight lasts a long time after the Sun has set and before it rises, because of all the dust in Mars' atmosphere.

At times, the Martian sky takes on a violet color, due to scattering of light by very small water ice particles in clouds.

The Earth and Moon appear starlike to the naked eye, but observers with telescopes would see them as crescents, with some detail visible.

An observer on Mars would be able to see the Moon orbiting around the Earth, and this would easily be visible to the naked eye.

At maximum angular separation, the Earth and Moon would be easily distinguished as a double planet, but about one week later they would merge into a single point of light (to the naked eye), and then about a week after that, the Moon would reach maximum angular separation on the opposite side.

The minimum angular separation would be less than 1′, and occasionally the Moon would be seen to transit in front of or pass behind (be occulted by) the Earth.

[8] At different times the actual magnitudes will vary considerably depending on distance and the phases of the Earth and Moon.

Phobos is still bright enough to cast shadows; Deimos is only slightly brighter than Venus is from Earth.

However, in the case of Deimos the term "transit" is appropriate, since it appears as a small dot on the Sun's disk.

It is easy to see that the shadow always falls on the "winter hemisphere", except when it crosses the equator during the vernal and the autumnal equinoxes.

In either case, the two intervals when transits can take place occur more or less symmetrically before and after the winter solstice (however, the large eccentricity of Mars's orbit prevents true symmetry).

Phobos and Deimos both have synchronous rotation, which means that they have a "far side" that observers on the surface of Mars can't see.

[citation needed] Since Mars has an atmosphere that is relatively transparent at optical wavelengths (just like Earth, albeit much thinner), meteors will occasionally be seen.

[12] As on Earth, when a meteor is large enough to actually impact with the surface (without burning up completely in the atmosphere), it becomes a meteorite.

The top two stars in the Northern Cross, Sadr and Deneb, point to the north celestial pole of Mars.

The orientation of Deneb and Sadr would make a useful clock hand for telling sidereal time.

As on Earth, Mars experiences Milankovitch cycles that cause its axial tilt (obliquity) and orbital eccentricity to vary over long periods of time, which has long-term effects on its climate.