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For the first time, humans have detected an interstellar asteroid—a space rock they're calling 'Oumuamua, which is a Hawaiian word meaning "scout." It's the only object we've ever seen that entered the solar system from beyond our little collection of planets. That's a pretty big deal on its own. But on top of that, this asteroid has a really interesting shape: It's very long and skinny, with a width to length ratio of about 1 to 10.

Basically, it looks like a cigar—or at least that's what everyone is saying. The only images we have that show its shape in detail are artistic renderings. Because the asteroid is so relatively small and far away, you can't easily see it with a visible-light telescope.

But if you can't see it, how can you describe it? The answer to this (as in many situations in science) is to use indirect observations. The one thing that can be measured is the brightness of the object. Because this rock is also spinning, the light it reflects from the sun changes over time. By looking at the ratio of the brightest to weakest observations, you can get an estimate of largest to smallest size. If you estimate the albedo (a measure of reflectance), you can also estimate the total size. Boom. There you have it—a cigar-shaped asteroid.

If you want to learn the answers to more "how do you know"-type questions about 'Oumuamua, check out this awesome NASA FAQ. But if you want to calculate some answers for yourself—well, just keep reading.

To read more, click here.
Category: Science