What is the Most Powerful Telescope in the World?

Just how powerful is the world’s most powerful telescope?

Let’s start with the human eye. The human eye has an angular resolution of about 1 arcminute. That's pretty impressive. Take a circle surrounding you on the horizon, divide it into 360 little bits, called degrees, and then you divide each of those degree into 60 arcminutes. One of those little slices is the angular resolution of the human eye. We can translate this into linear resolution based on the distance of the thing we're observing. So if you're looking at something about one kilometer away, you can distinguish two points if they're separated by at least about a third of a meter.

But if you hold your finger up nice and close to your eye, you can see the tiny millimeter-level differences in the markings of your fingerprint. You cannot make out a fingerprint sitting a kilometer away, and you can very easily distinguish something that is separated by a third of a meter if it's in the same room as you. The angular resolution allows us to translate and calculate our linear resolution for whatever distant object we are studying, which is why it's so handy in astronomy.

So let's kick things up a notch and jump right to the James Webb Space Telescope. That instrument's primary mirror is 6.5 meters across, which is so big it couldn't even fit inside of the rocket and we had to fold it up and devise all these clever, origami-like schemes to get it to up in space. That gives the telescope an angular resolution around a tenth of an arcsecond.

So you take the human eye resolution, which is already pretty impressive. You divide that by 60 to go from arcminutes to arcseconds, and then you divide by ten to get a tenth of an arcsecond. So right there, the resolution of the James Webb Space Telescope is six hundred times better than the human eye. To give some fun examples, the James Webb could see the details of a coin placed forty kilometers away from it, or it could pick up the pattern of a regulation soccer ball sitting 550 kilometers away from the telescope. It's an impressive telescope.

But we can all agree that the James Webb was kind of a pain to make. It was a decade late. It was billions of dollars over budget. We like that it's there now, but it wasn't fun in the lead-up to it.

So in astronomy, the only way to get higher resolution is to have a bigger dish, but bigger dishes are hard to do. Thankfully, there are some ways to cheat. One way is with a technique called interferometry where you don't have a single large dish. Instead, you have lots of small independent dishes, and then you cleverly correlate their answers together.

This technique allows you to take their independent measurements and stitch together a larger image of that. One of the best examples of this technique is called the Event Horizon Telescope. This is what we've used to observe the ring of material around distant black holes.

The telescope itself is made of instruments scattered all across the globe. So it effectively turns the Earth into a single astronomical collecting instrument.

There are some downsides to interferometers because you can only pick up signals where your instrument is. If light just hits dirt, like the ground next to your telescope, you don't get to fold that into the image. So there's this whole complicated business of turning these into images. But at the end of the day, it gives you insanely high resolution.

The resolution of the Event Horizon Telescope is 20 microarcseconds. A delightful example given by the Event Horizon Telescope folks is that they could spot an orange sitting on the surface of the moon. That's how high of a resolution they have.

Using tricks like this, astronomers have unlocked the wonders of the universe and explored the mysteries of the cosmos.