As an astronomer studying the universe beyond Earth, I like “off the beaten path” views almost by default. But one of my favorites is when a spaceship takes a snapshot of our homeworld and the moon from a great distance. Stuck here on the planet’s surface, our mundane perspective is rarely questioned, so seeing our world and its only natural satellite side by side is a rare gift, a shock to our cosmic complacency.
Sometimes the image shows both objects in detail, as the DSCOVR satellite did in 2015. Sometimes the Earth and Moon are blurry and pixelated, as they were in a 2003 photo from the European Space Agency’s Mars Express mission, giving a certain impression of distance. Most often, they are just dots, points of light almost lost among the stars, as the Psyche mission saw from 290 million kilometers away in July 2025. The smaller we appear in these images, the easier it is to appreciate the depth of space and the way we actually float on an ocean of black.
Another, even rarer view is to observe our planet from the surface of another world, which only happened in 2004, when NASA’s Spirit rover on Mars took an image of Earth in this alien sky. In the black-and-white photo, Earth hangs in the pearly glow of Martian twilight, the rolling horizon silhouetted against the background. It’s an image that almost makes us wonder what it would be like to stand there on the Red Planet and see it for ourselves. What would it look like to us? Could we also see the moon next to our blue world?
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Earth appears as a barely visible dot in this first-of-its-kind image of our home planet, seen by NASA’s Spirit rover from the surface of Mars on March 8, 2004.
As usual when you look at the sky, what you see depends on when you look. Both Earth and Mars orbit the Sun at different speeds, which dramatically changes the perspective. At their closest point, when they are on the same side of the sun, Mars and Earth are about 55 million kilometers apart. However, when they are on opposite sides, this distance extends to 400 million kilometers!
This influences two crucial factors in viewing the Earth and Moon as a pair in the Martian sky: the distance between them and their brightness.
You would think that the Earth and Moon would be brightest when they are closest to Mars, because brightness depends on distance. But that’s not the case! When the two planets are closest to each other, they are on the same side of the Sun, which places Earth between Mars and the sun. This means that, from Mars, you would be looking at the unlit night side of Earth. It is obviously dark, which makes the Earth dark.
When the Earth is opposite Mars when viewed from the sun will appear full because you are looking directly at the daylight side. But this problem is mitigated by its much greater distance, as well as the fact that Earth appears much smaller in the sky. So what’s irritating is that when it’s closest to Mars it’s weak, and when it’s furthest from Mars it’s also weak!
There East a happy medium though. As the Earth orbits the sun, from Mars, it appears to go through phases, much like the Moon does when viewed from Earth. This phasing depends on the observation geometry: the Earth is full on the opposite side of the sun and “new” (like the dark new moon) when it is between Mars and the sun. Between these two extremes, our planet will appear as a crescent or half-full or gibbous (between half and full) during this orbit. Note that the Moon will display the same phase as the Earth; because we are looking from Mars, the angle between the Earth and the Sun is essentially the same as that between the Moon and the Sun, so their phases are identical.
A view of the Earth-Moon system, as captured by the European Space Agency’s Mars Express spacecraft from a distance of 8 million kilometers on July 3, 2003.
ESA/DLR/Free University of Berlin
Surprisingly, the Earth will appear brighter when it is in its crescent phase. Although it appears thinner, this happens when Earth’s crescent is closer to Mars, making it appear larger in the sky. The size of the lit part you see in the sky is actually larger than when it’s full, making it proportionately brighter.
This is exactly the same situation that we observe from Earth when we look at Venus in the sky. Venus also undergoes phases and appears brightest to us when it is a large crescent. This means that the best time from Mars to see the Earth and Moon together is a few weeks after their closest approach. They will be brighter and still well separated in the sky.
How bright will they be? From Mars, at that time, Earth will be at around magnitude -1 or -2 at best, which is about as bright as Jupiter appears in Earth’s night sky. It’s not as showy as Venus but is still quite bright and easy to spot. The moon will be a nearby “star” with a magnitude of about 2 or 3, about the same apparent brightness as the stars of the Big Dipper. (The brighter a celestial object, the lower its magnitude number, on the inverse logarithmic scale used by astronomers.)
But brightness isn’t the only thing to consider here. If you want to see both the Earth and the Moon, they need to be separated enough in the sky to be discerned individually. If they are too close together, the human eye will blend them into one object. How far apart they are in the sky of course depends on their distance from Mars – the closer they are to Mars, the further apart they will be – but it also depends on where the Moon is in its orbit as seen from Mars; as it orbits the Earth, their separation will also appear to change. But suppose we get lucky and see them as geometrically distant as possible.
When the pair is closest to Mars, at most, the Earth and Moon will be just under half a degree apart in the sky (astronomers measure the size of the sky in degrees, where there are 90 degrees from the horizon to the zenith). It’s easy enough to see them as two separate objects, even with the difference in brightness. When on the opposite side of the sun, they are only one-eighth that distance apart, making them much harder to tell apart. If we choose the time when they appear brightest, as thick crescents, they will be separated by about a third of a degree, far enough apart to be seen individually. However, there still remains a problem.
The Earth is about four times wider than the Moon and much brighter; our surface and cloudy air reflect sunlight about three times better than the gray surface of the moon. In total, this means that the Earth is about 50 times brighter than the Moon when viewed from a distance. This poses a problem of contrast; they must be far enough apart in the sky so that the moon is not lost in the glare of the Earth!
Putting it all together, if the orbital geometries all align just like that, I find that the Moon and Earth will indeed be visible in the Martian sky as two separate objects, although you may have to squint a little to see the much fainter moon. If you have binoculars, you may be able to spot the Moon and Earth in the same phase. A telescope would reveal Earth’s continents and oceans; in fact, Earth’s brightness and even its color can change as the planet rotates or when you see cloudy or clear weather.
After all this, I wonder: When will any of us actually stand on the dusty surface of Mars and see Earth hanging in darkness near the horizon? And even further: If they’ve been on Mars long enough, will they look at that bright beacon in the sky and still see it as home?
Many thanks to my friend (and course agent) Beth Quittman for asking me this question.
