Science and Exploration

[dreadgeek]

It was pointed out to me that 2.5 orders of magnitude might be a little difficult for people to grasp intuitively so to give you a sense of scale I'll use this. I live in Portland, OR but I work in Hillsboro, OR. That's about 20 miles one-way, door-to-door from home to office. One order of magnitude would be ten times that far or 200 miles. That would put me in Grants Pass, OR or just north of Seattle, WA. Two orders of magnitude would be 2000 miles away so that would be in the Detroit, MI region. Two and half orders of magnitude would be 3000 miles or somewhere in northern Maine.

So to understand the scale of distance between the Moon and Earth compared to Mars and Earth, do this; take a city that is around 25 miles from you. Find a city that is ten times that distance (one order of magnitude) away. Now, find a city that is 100 times further away (two orders of magnitude). Now find another city that is half-again as far away (two and half orders of magnitude) and THAT is the ratio of distance scaled down to terrestrial scales. . So, to scale, the Earth is as far away from Mars as Portland, OR is from northern Maine. The Earth is as far away from the Moon as Portland, OR is from Seattle WA.

Originally Posted by dreadgeek

As Phil Plaitt points out in this article, every year around this time people start spreading this Internet meme that Mars will look as large as the Moon in the night sky. It's a hoax. It will always be a hoax because Mars *never* gets close enough to Earth to look as large as the Moon. At its closest pass Mars gets within 35 million miles of Earth. At its farthest point (where it is now) it is about 210 million miles from Earth (it's currently on the far side of the Sun from us). Mars is a relatively small planet. It is half the size of Earth. The moon is about half the size of Mars. The moon is just next door (250,000 miles) compared with with the 35 million miles between Earth and Mars at their closest. So in order for this meme to be true, an object only twice the size of our moon would have to appear to be the same size even though Mars is two and a half orders of magnitude farther away from Earth! That's not optically *possible*. With the naked eye Mars can only ever look like a tiny dot in the sky. If it ever *were* in an orbit that would make it look the same size as the Moon that would be a very interesting day on Earth (interesting, here, in the "Oh God, Oh God, we're all gonna die" sense).

So if you see a meme on Facebook telling you that if you go outside sometime in the next week it'll appear as if the planet has two moons, know that someone is pulling your leg because they are.

Cheers
Aj