The moon the same size as Mars? Oh dear. I first stumbled upon this suspicious fact one day on Facebook. It had received hundreds of thousands of likes and shares. But, as an amateur astronomer I knew that it wasn’t right, it couldn’t be right. After all, Mars is a planet that’s a hell of a long way away, and the moon is only the moon. They can’t appear to be the same size from Earth, ever. So I felt compelled to debunk it here.
This is a myth that has been circulating since about 2003 and really serves no other purpose but to keep people up late at night. The myth constantly states that the moon will be the same size as Mars in August, or some time in summer. It sometimes even accompanies a photo of what looks like two moons, with one being the moon and the other Mars (one example is pictured here). Now I must admit that this would be cool if it were true, but it isn’t. The reason is that Mars isn’t that big and it is far too far away from Earth to ever appear the same size.
The brightest planet in the solar system as viewed from Earth is Venus followed by the giant Jupiter. Mars can occasionally challenge Jupiter for brightness, but this is rare. To clarify this even further, the diameter of Mars when viewed from Earth is only ever about 1/140th that of a full moon. So basically, it’s tiny. If it were the same size we would be able to see the polar ice caps with the naked eye, something that requires a telescope with an aperture of at least 200 mm (8 inches). You may even be able to see Olympus Mons, the solar systems largest mountain, and possibly even the ravines. But the massive distance doesn’t even contend with the huge and catastrophic impact such a close encounter would have on our own planet.
Imagine for a moment what would happen to Earth if Mars was close enough to look like the moon. As you may already know, the moon affects the tide, so what would be the impact if a planet were close enough to our own planet? The tide would be disastrous, to say the least. It could even possibly affect our own orbit, which wouldn’t exactly be an environmentally good outcome for our own planet.
So the next time you see this myth in an email or on social media, don’t stay up late for it. You will be disappointed. The moon same size as Mars, you have to be kidding me.