As an astronomer studying the universe beyond Earth, I’m fond of “outside the box” views almost by default. But one of my favorites is whenever a spacecraft takes a snapshot of our home world and the moon from a great distance. Stuck here on the planet’s surface, our mundane perspective is rarely challenged, so seeing both our world and its lone natural satellite side by side is a rare gift, a jolt to our cosmic complacence.
Sometimes the image shows both objects in detail, as the DSCOVR satellite did in 2015. Sometimes the Earth and moon are fuzzy and pixelated, like they were in a shot from 2003 by the European Space Agency’s Mars Express mission, giving some sense of distance. More often they’re just dots, points of light that are 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 just how deep space is and how we are truly afloat on an ocean of black.
Another, even rarer view is to see our planet from the surface of another world—something, in fact, that first occurred only in 2004, when NASA’s Spirit rover on Mars snapped an image of Earth in that alien sky. In the black-and-white shot Earth is hanging in the pearly glow of the Martian twilight, the hilly horizon silhouetted at the bottom. It’s an image that almost begs us to wonder how it would feel to stand there on the Red Planet and see it for ourselves. What would it look like to our eyes? Could we also see the moon next to our blue world?
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Earth appears as a scarcely visible dot in this first-of-its-kind image of our home planet, as seen by NASA’s Spirit rover from the surface of Mars on March 8, 2004.
As usual when you’re looking at the sky, what you see depends on when you’re looking. Earth and Mars both orbit the sun at different rates, and that changes the perspective drastically. At their absolute closest—when they’re on the same side of the sun—Mars and Earth are about 55 million km apart. When they’re on opposite sides, though, that distance stretches to 400 million km!
This influences two crucial factors in viewing Earth and the moon as a pair in the Martian sky: how far apart they appear, and how bright they are.
You’d think Earth and the moon would be brightest when they’re closest to Mars because brightness depends on distance. But this isn’t the case! When the two planets are closest together, they’re on the same side of the sun, putting Earth between Mars and the sun. This means that, from Mars, you’d be looking at Earth’s unilluminated night side. That’s dark, obviously, making Earth appear dim.
When Earth is opposite Mars from the sun, it will appear full because you’re looking directly on the daylit side. But mitigating this is its far greater distance, plus the fact that Earth appears much smaller in the sky. So, irritatingly, when it’s closest to Mars, it’s faint, and when it’s farthest from Mars, it’s also faint!
There is a happy medium, however. As Earth orbits the sun, from Mars, it will appear to go through phases, much like the moon does as seen from Earth. This phasing depends on the viewing geometry: Earth is full on the opposite side of the sun and “new” (like the dark new moon) when it’s between Mars and the sun. In between these two extremes our planet will appear as a crescent or half full or gibbous (between half and full) over the course of that orbit. Note that the moon will show the same phase as Earth; because we’re looking from Mars, the angle between Earth and the sun is essentially the same as it is for the moon and the sun, so their phases are identical.
Surprisingly, Earth will appear brightest when in its crescent phase. Even though it appears slimmer, this happens when the crescent Earth is closer to Mars, making it appear bigger in the sky. The size on the sky of the illuminated portion you see is actually bigger than when it’s full, making it proportionally brighter.
This is exactly the same situation we see from Earth when we look at Venus in the sky. Venus also undergoes phases and appears brightest to us when it’s a fat crescent. This means the best time from Mars to see Earth and the moon together is a few weeks after their closest approach. They’ll be brighter and still well-separated in the sky.
How bright will they be? From Mars, at this time, Earth will be at a magnitude of about –1 or –2 at best, which is about as bright as Jupiter appears in Earth’s night sky. That’s not as flashy as Venus but still quite brilliant and easy to spot. The moon will be a “star” nearby at a magnitude of roughly 2 or 3, about the same apparent brightness as the stars in the Big Dipper. (The brighter a celestial object, the lower its magnitude number, in the reverse-logarithmic scale used by astronomers.)
But brightness isn’t all there is to consider here. If you want to see both Earth and the moon, they must be separated enough in the sky to be discerned individually. If they’re too close together, the human eye will blur them together into a single object. How far apart they appear in the sky depends on their distance from Mars, of course—the closer they are to Mars, the farther apart they’ll be—but it also depends on where the moon is in its orbit as seen from Mars; as it circles around Earth, their separation will appear to change as well. But let’s assume we have good luck and happen to see them as geometrically far apart as possible.
When the pair is closest to Mars, at maximum, Earth and the moon will be just under half a degree apart in the sky (astronomers measure size on the sky in degrees, where there are 90 degrees from the horizon to the zenith). That’s easily enough to see them as two distinct objects, even with the brightness difference. When they’re on the opposite side of the sun, they’re only an eighth that distance apart, making them much more difficult to distinguish. If we choose the time when they appear brightest, as thick crescents, they’ll be separated by about one third of a degree—far enough apart to see individually. There’s still one more issue, however.
Earth is about four times wider than the moon and far shinier; our surface and cloudy air reflect sunlight about three times better than the moon’s gray surface. Altogether, this means Earth is roughly 50 times brighter than the moon when seen from a distance. This makes contrast a problem; they have to be far enough apart in the sky that the moon isn’t lost in Earth’s glare!
Putting all this together, if the orbital geometries all align just so, I find that the moon and Earth will indeed be visible in the Martian sky as two separate objects, though you might have to squint a bit to see the much fainter moon. If you have binoculars, you might be able to spot both the moon and Earth sporting the same phase. A telescope would reveal Earth’s continents and oceans; in fact, Earth’s brightness and even its color might change as the planet rotates or when you see a cloudy versus a clear day.
After all this, I have to wonder: When will one of us actually stand on the dusty surface of Mars and see Earth hanging in the gloaming near the horizon? And even further off: If they’ve been on Mars long enough, will they look at that gleaming beacon in the sky and still see it as home?
Many thanks to my friend (and lecture agent) Beth Quittman for asking me this question.
