I understand that the bigger your telescope’s dish/mirror, the more information you receive and the better your image/data. But why does an array of relatively small dishes spread out over a mile (for example) get treated as having similar data collection powers as a single dish a mile across?
It’s this lazy reporting? Me misunderstanding? Some complex concept that I don’t understand?
Logically (to me) three twenty meter dishes should only collect three times the data of a single twenty meter dish. What an I missing?
In: 5
Generally that only works for a radiotelescope. So whatever we get, it’s not a visible image anyways, but rather an image that we translate from radio waves.
For example, when we got the images of the black hole using radio telescopes all over the Earth, we were trying to simulate a telescope the size of the Earth.
When trying to differentiate between light sources, if they are too far away, they get smaller, and too small, we can’t differentiate between them. The theoretical maximum for angular resolution of a telescope is θ = 1.22λ/D where that’s angular separation of the features you’re trying to identify in radians, wavelength of light, and diameter of the telescope.
To put angular resolution into perspective, holding your thumb at arm’s length is about 1° wide in your field of view, the moon is about 1/2°.
So we want a big telescope, but we can’t actually cover the Earth with one big telescope, so we use our knowledge of how light moves and the smaller telescopes as data points, and we fill in the blanks around it until we get one image.
That’s a bit complex … not sure if I can actually ELI5 it.
Maybe a visualisation helps, though it might not be entirely correct.
For a telescope the resolution is calculated by the wavelength and the diameter of the mirror. The larger the mirror, the better the resolution.
Now imagine a 100 meter diameter mirror. It has some resolution. If you make a hole in it, the diameter stays the same. So the resolution is the same. If you keep making the hole bigger, the diameter will still stay the same, although most of the mirror is gone.
Where this now breaks down is that you have a ring instead of two single points. But now imagine you split the ring in multiple segments, now you have a lot of single mirrors but the resolution still stays the same. Not a perfect analogy, but the basics are still the same. In terms of resolution two distant dishes (in Radio) working together have the same resolution as one big dish.
The difference is the mich lower collectin area which collect the light and reflect it to the receiver.
But the advantage is that it is much easier to build.
The more area your dish/lens/mirror/arbitrary aperture has the more photons you catch (visible, IR, radio, all photons) which gives you a brighter/stronger signal. This lets you see dimmer stars or pick up smaller asteroids on radar because the signal doesn’t get washed out by the sensor’s standard noise
The further apart the edges are the better you can discern fine detail and the less impacted by edge effects your final image is.
Each of the telescopes still works like a normal telescope, but if you can pipe all their data together then you can start treating them like a bigger one. What ends up mattering is the angles from the outside of your aperture to the target and by making the aperture bigger the angles get bigger and you can discern smaller details. If your aperture is too small then it doesn’t matter how bright your image is because the fuzzing from edge effects is going to mean everything is fuzzy no matter what you do.
So you’re on the right track. Three 20 meter dishes can collect 3x as many photons as 1 20 meter dish, but if spaced carefully and well measured they can give you better resolution but you’re still only going to see things that are a third as bring as your single telescope could
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