Stargazing On Mars

A pink and blue Mars sunset photographed by NASA's Pathfinder rover. Credit: NASA
A pink and blue Mars sunset photographed by NASA’s Pathfinder rover. Credit: NASA

We’re stuck with Earth for now when it comes to stargazing. And despite the plague of light pollution, it’s still a pretty good planet for looking up. But thanks to planetarium-style software, we can easily jaunt off to Mars and get an inkling of what the night sky has to offer on a different planet. No stray light there except a hint of airglow from the Martian atmosphere and starlight. Just enough to find your way at night across the dunes and rocks. I’d bring a headlamp to be safe!

A raw color image from NASA's Curiosity Rover shows how Mars looks under that planet's lighting conditions. For scale, the distance between the parallel wheel tracks is about 9 feet (2.7 meters). Credit: NASA/JPL-Caltech
A raw color image from NASA’s Curiosity Rover shows how Mars looks under that planet’s lighting conditions. For scale, the distance between the parallel wheel tracks is about 9 feet (2.7 meters). Surface temps can reach as high as 70° F on Mars, but nighttime lows are typically around -80° F! Credit: NASA/JPL-Caltech

The Martian sky is the color of butterscotch during the day. In the evening around sunset, we’d see familiar pinks, yellows and oranges in the west but also an unexpected bluish glow around the sun caused by light scattered from very fine dust in the atmosphere directed back to our eyes. Just as on Earth, skywatchers on the Red Planet would experience dusk and dawn, but these transition times would last longer than typical twilights on our planet because of so much dust suspended in the air. Dust reflects light, keeping the sky bright.

Once darkness finally settled in, the constellations would appear identical and the limiting magnitude — the faintest star visible with the naked eye — would be very similar to a dark sky on our own planet with stars visible down to about magnitude +6. Stars are all so far away that no matter what planet you chose, the constellations would all look the same.

Mars' axis is tilted almost the same as Earth's, so it has seasons, too. Each lasts about twice as long because Mars takes longer to revolve around the sun.
Mars’ axis is tilted almost the same as Earth’s, so it has seasons, too. Each lasts about twice as long because the planet takes longer to revolve around the sun. Credit: NASA

A careful observer would notice a few differences however. Mars’s axis is tilted 25° or a bit more than Earth’s 23.5°. This causes the sun’s path to be slightly more extreme, causing it appear a tad higher at its summer high point and a tad lower at its winter low point. Also, Mars lacks auroras. At least ones visible to the naked eye. The planet has no enshrouding magnetic field. Instead, there are locally magnetized regions over which very weak auroras occasionally appear.

The north pole of Mars points to a point in the sky as well. Instead of Polaris, it’s aimed at an empty spot of sky between Deneb in the Northern Cross and the constellation Cepheus. Sadly, Mars currently has no naked eye pole star. Not at the south pole either, which points toward the “False Cross” asterism in Vela. Because Deneb and the constellation Cygnus lie near the north pole of Mars’ sky, mid-northern hemisphere observers would get to see the bright Cygnus section of the Milky Way every night of the year.

An observer on the Red Planet would see meteors flash overhead along with the occasional bright fireball and even a few satellites. There are 13 of them orbiting the planet (as of Oct. 2015) of which only five are still active. Of course there would be no moon as we have here on Earth, but in its place we’d see two smaller ones — Phobos and Deimos. They’re tiny with diameters of only 14 miles (22 km) and 8 miles (12.6 km) respectively.

Phobos orbits so close to Mars that instead of properly rising in the east and setting in the west like the rest of the stars and Deimos, it rises in the west and sets in the east twice per Martian day or sol, equal to 24 hours and 37 minutes. Only one-third the size of the moon as seen from Earth, Phobos’ phase would change visibly with the naked eye hour by hour, thickening from crescent to full overnight. When in full phase, the little moon would shine at around magnitude -10 — very bright — but some 15 times fainter than our full moon.

Two small, irregular-shaped moons, Phobos and Deimos, orbit Mars and provide lots of fine conjunctions with each other and bright stars in the Martian sky. Credit: NASA-JPL Caltech
Two small, irregular-shaped moons, Phobos and Deimos, orbit Mars and provide lots of fine conjunctions with each other and bright stars in the Martian sky. Credit: NASA-JPL Caltech

Deimos rises normally in the east but because its orbits Mars once every 30 hours (our moon takes 27 days), nearly the pace of Mars’ rotation, it lingers above the horizon about two and half days before finally setting in the west. Too small to show a shape with the naked eye, Deimos shines a little brighter than Venus does from Earth.

If you were camped next to the Curiosity Rover this morning at dawn and faced east, you would have seen the Earth low in the eastern sky. Higher up, Phobos and Deimos would have made a bright and impressive display. The rover is located near the planet's equator. Map: Bob King, source: Stellarium
If you were camped next to the Curiosity Rover this morning at dawn and faced east, you would have seen the Earth low in the eastern sky. Higher up, Phobos and Deimos would have made a bright and impressive display. The rover is located near the planet’s equator. Stellarium

If instead of observing during the evening, we chose to rise at dawn,  a most wonderful sight would greet our gaze this month. Low in the eastern sky, we’d spy a bright, pale blue “morning star” planet, none other than the Earth. And next to it, the moon! When Earth and Mars get close to one another as they are this year, the moon would be appear alongside the Earth and look like a double planet (Earth much brighter) with the naked eye. A week later the moon would go around the back side of Earth and disappear and then return to view off to the opposite side of the planet a week after that. When Mars and Earth are at their most distant, it would take eagle-eye vision to split the two.

This is the simulated sky at the very start of dawn today June 23, 2016
This is the simulated sky at the Curiosity rover location in Gale Crater at the start of dawn today June 23, 2016. Stellarium

Uh-oh. The sun’s rising and already Earth will soon fade from view in the gathering light. I hope you enjoyed your night on the Red Planet. We’ll come back again for another visit soon.