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Wednesday, October 22, 2008


The theoretical ability of a telescope to resolve images is directly proportional to its size. The largest is a 11.4m aperture one in the Mount Graham International Observatory. It is built of segmented mirrors because the larger the mirror the more distortions that are inevitable if it is created in a gravity field.

Another problem is that on Earth we are looking through atmosphere. This is why all the wonderful pictures recently have come from the Hubble Space Telescope despite its 2.4m aperture. Like this

But what is the maximum size of a telescope built in space?

I have no idea. A perfectly circular shape can be achieved in zero G simple by spray painting a balloon since a balloon has no other forces acting on it other than gas pressure if there is no gravity & can thus be a perfect sphere. I can see no near term size limits on such mirrors. A mirror with a 1km diameter will collect 10,000 times as much light as a 10m one, or 16,000 times more than the Hubble.

Beyond that, because photons can be collected with an accuracy of timing that is truly unbelievable, it is now possible to correlate images from more than one telescope & putting them together producing together an image that cann be resolved as if the diameter of the telescope was the distance between the 2 of them, though obviously without any more light photons being received.
The telescopes can work together, in groups of two or three, to form a giant ‘interferometer’, the ESO Very Large Telescope Interferometer, allowing astronomers to see details corresponding to a much larger telescope. Of course on Earth weather makes that less useful & in any case they cannot get more than 8,000 miles apart.

Earth's orbit has a diameter of 200,000,000 miles.

At that level there is nothing we could not observe from the start of the universe to the planet a mere 4 light years away. I am not dealing with spacecraft beyond the solar system in these articles because they, probably, need theoretical breakthroughs in science & are therefore well beyond engineering which applies the science we already know. Nonetheless when such a time comes we will already have photographs of anywhere we want to visit.

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