Because both planets orbit the sun in different shapes, they are never the same distance from one another.
At precisely 10.51am on Wednesday the red planet was 34.6 million miles from us.
People in the UK will have to wait until it's dark to see the planet, because light from the sun will make Mars hard to see.
But if you have a telescope, you'll be able to make out details on the planet's surface.
Robin Scagell, from the Society for Popular Astronomy, said, "You will certainly see the south polar cap, which is really glistening at the moment."
Mars won't get this close again until 28 August, 2287!
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