You probably recognize this image. You see something like it whenever you look up at the sky. Some days are clearer than others—some, you might even see a completely blue sky—but regardless, you know that this is an image of our atmosphere.
But do you know just how much your atmosphere does for you?
We’ll talk about how it protects you from space rocks later on. For now, consider the energy from our own sun. The sun doesn’t just send visible light our way—it operates in all wavelengths of the electromagnetic spectrum.
Some of those wavelengths are harmful, like gamma rays, X-rays, and ultraviolet radiation. Others, like infrared radiation, microwaves, and radio waves, are perfectly fine.
The atmosphere doesn’t really pick and choose which wavelengths get through to the surface. It blocks out some radiation it doesn’t need to. At least it protects us from the harmful wavelengths.
But that’s bad news for astronomers, because those wavelengths still contain useful information about the universe.
It’s a radio telescope, the largest in the world. It’s so huge that a normal support system can’t support its weight. So it’s basically suspended between three mountaintops. It’s 300 m across, which is 1000 feet. It’s huge.
This is the kind of construction endeavor that radio astronomers must try if they want to get much detail from radio waves. The radio wavelengths of the electromagnetic spectrum are really, really weak. You need huge telescopes to collect enough.
But, as ever, astronomers face the same basic problem: money.
Huge telescopes are expensive. It’s unfortunate for astronomers, but true—just think of the cost of labor of basically burying a whole valley under a radio dish.
Astronomy is a labor of love, and radio astronomy is no different.
As I covered in my last post, radio astronomy deals with the longest wavelengths of the electromagnetic spectrum (a spectrum that includes visible light). Radio waves are not sound waves. They’re radiation just like visible light, infrared, and ultraviolet.
I’ll prove to you that radio waves can’t be sound waves. We get them from space—that’s why there’s such a thing as radio astronomy. But there’s no sound in space. Why? Sound requires something to pass through, and space is a vacuum.
So, we’ve established that radio waves are just another form of electromagnetic radiation. And astronomers love to collect any form of electromagnetic radiation. We can’t touch the stars ourselves, so it’s our only chance at learning about the cosmos.
Why? Because just about everything in the sky emits electromagnetic radiation.
Everything except black holes and a couple other things…but those are topics for another day.
But electromagnetic radiation isn’t easy to collect. And radio waves are especially hard.
Yeah, it’s a bit bigger than your average radio antenna.
That’s because its job isn’t to direct radio signals to your house. It’s a radio telescope, and its job is to collect as many radio signals as it possibly can—from outer space, not from a radio station.
Radio astronomy is a tricky business. It has its advantages over visible astronomy—it certainly works better for interferometers—but radio signals are so weak, they’re hard to detect and study. Which is why you’ll never see a small radio telescope.
So, how do astronomers manage to collect and study radio emissions from the cosmos?
Okay, maybe you have…online. What with the spread of the internet these days, I’m guessing that at one point you have seen something like this on a page of image search results.
That’s the thing, though. You’ve seen this incredible phenomenon on a computer screen. But have you ever seen it through a telescope?
Don’t worry—if you haven’t had an opportunity to look through a telescope, you’re not missing out. You’re not going to see the Sombrero Galaxy above in all its photographed glory just from looking through the eyepiece of a telescope.
Imagine you have an image like this. This object is faint and faraway, so you can’t make out much more detail. You know that other stars like it—closer, brighter stars—have looked like this and turned out to be two stars, nestled very close together.
How do you figure out what you’re looking at? How do you increase the resolving power on your telescope so that you can make out more detail?
A telescope’s resolving power is limited by its size. Bigger telescopes can make out more detail on faraway objects—that’s because they can gather more light. But now, we can make telescopes that are so big their size doesn’t limit their resolving power anymore.
The atmosphere does.
We obviously can’t change the atmosphere. So how do we get around this particular predicament?
Okay, so maybe I sort of gave it away in the post title…
I know what you’re about to say next. Why are we looking at a mount? What’s so special about a mount—isn’t the telescope itself more important?
And the fact is…I know where you’re going with that. The telescope is important, and without it, the mount would have no purpose. But without the mount, the telescope would be lost—it would have power, but nothing to do.
Can you tell the difference between these two telescopes?
I’ll give you a hint. They are bothreflectors. I know I wrote before that you’ll normally find the eyepiece (the little bit tacked onto the telescope tube) on the side with reflectors, but as you can see here, this isn’t always the case.
Here’s another hint. The mounting setup isn’t the difference I’m talking about. I realize the most obvious difference is probably that one is on a “fork mount” (right) and the other is on an equatorial mount (left), but I’m thinking of something related to the optics.