Solar eclipses are a stunning natural show where the moon, some 3500-kilometers across, almost exactly covers the 1.4-million kilometer diameter sun for a few precious minutes, darkening the skies and revealing the faint Solar corona.
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They are perhaps the most grand display of something we humans all intuitively know - things that are further away appear smaller to our eyes.
For example: you could exactly cover the moon with a dollar coin held about 2.8-metres from your eyes. Despite the distance, it would still be possible to make out some detail on the coin, but certainly not as much as when looking up close. Taking things further, what if we decided to cover another star, all of which are very, very far away?
Betelgeuse is one of the brightest stars in the sky - a red supergiant in the constellation of Orion. Supergiants are big - if we replaced the sun with Betelgeuse it would be about twice as large as the orbit of Mars. However Betelgeuse is 700 light years, or 6,600,000,000,000,000 kilometers, distant and thus appears 36,000 times smaller than the sun. Our dollar coin is now 103 kilometers away and our eyes have no chance. Fortunately however, humans invented telescopes.
The largest telescopes in existence are practically steerable high-rise buildings.
To see more detail on this coin, we need to increase our resolution - effectively allowing us to "zoom in". The best resolution possible is set by how much light you can collect - think the pupil for an eye, versus the lenses on a pair of binoculars. By having lenses larger than your pupil, binoculars (or telescopes) let you see extra detail you couldn't with your eyes alone.
The largest telescopes currently in existence, practically steerable high-rise buildings, have mirrors about 8-10 metres in diameter - just big enough to see detail on a star like Betelgeuse.
What if we wanted even more resolution though?
Recall that resolution is determined by the size of your lens or mirror. Well, it turns out this still holds true even if your mirrors aren't actually physically connected. If you put two 1-meter diameter telescopes at either end of a football field and combine the light just right, you get a telescope with the resolution of one the size of a football field. While we obviously can't collect the same amount of light as a football field-sized telescope, it allows us to see things in much more detail than our 8-metre telescope - equivalent to our dollar coin being thousands of kilometers away!
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This allows for some incredible science, such as studying stars spinning so fast they've become flattened, or stars still making planets from discs of leftover gas and dust around them. For radio telescopes it becomes possible to combine the light from telescopes much further apart than a single football field, letting you see distant galaxies, giant clouds of hydrogen gas, or, when combining light from telescopes literally on the other side of the planet - black holes.
Thus telescopes can be as different as the kinds of science they're doing and, just like people, it takes all kinds to discover the many mysteries of the universe yet to be unravelled.
- Adam Rains is an astronomy PhD student at the ANU.
