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Can One See the Martian Moons Phobos and Deimos without a Telescope?

-- Jamie | February 4, 2023

Question:

For the last few months in the Twin Cities, very clear nights. One night Mars looked almost like it was a hundred miles away. Many nights, including tonight, I see Mars. Clearly, there it is – a reddish dot – that I confirmed by location as being Mars. Right below, literally right next to Mars is a little dot. At first, I thought it was an optical illusion. I am not looking at it from a telescope, using a camera phone I magnified it enough to see that it is a distinct dot right below Mars. Then, I read that Mars has two moons just a few thousands miles away from it. And I am thinking there is no way I can see a moon of another Planet without a telescope. But no matter where I look on the Internet I cannot confirm that I am seeing a moon of Mars. Am I seeing one of Mars’ moons is my question.

-- Jamie

Answer:

Even when Mars is very close to the Earth, the two moons that orbit Mars, Phobos and Deimos, are simply too small to detect from Earth without at least a rather large backyard telescope. For example, during one of these past Martian close approaches, in 2018, Phobos’ maximum brightness was at magnitude +11, while Deimos was at magnitude +12. Recall that the human eye can see objects as dim as magnitude +6 or so (larger magnitudes are dimmer objects). More likely you were seeing a background star along the line of sight to Mars.

-- Jeff Mangum

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