seej500:

m1k3y:

I think it’s fair to say that, given your ‘druthers, you’d want an instrument that could map exoplanets in the kind of detail you get with Google Earth, with enough resolution to actually see the Great Wall of the Klingons, in case they’ve built one.

Could we construct such a telescope … ever?

…

An interesting discussion and worth a read, but in actual fact we sort-of already have telescopes that are bigger than this.  Like, almost twice the diameter.

Y’see, it used to be that to get your telescope to work you needed one big reflector. Bigger the reflector, better the resolution (in the strict physics sense of the word resolution, meaning the ability to distinguish objects as separate from each other).

The biggest single reflector is, as you probably know, the Arecibo radio telescope.  And that’s kind of unwieldy and pretty impractical, not least because you can’t point it at anything other than whatever is directly overhead.

Around the 1970s though, computing power got good enough that a new type of telescope became possible, and led to the construction of arrays of smaller dishes, probably the most famous example of which is the imaginatively-named Very Large Array in New Mexico.  With a bit of clever programming, the images from all those individual dishes can be stitched together to in effect make the whole thing behave like one really big dish, only with the benefits of being directional and much cheaper to build and maintain.

As computing power has increased, more and more of these array telescopes have been built.  MERLIN, one of my favourites because it’s British, takes the input from seven older dishes spread across a couple of hundred miles of the Midlands, puts it all together, and gives you an effective telescope diameter that would be impossible to construct as a single dish (well, unless you had a budget of trillions of pounds and felt like dooming Birmingham and the rest of central England to permanent darkness).

But even with this technology, we’re limited by the size of the Earth, with a diameter of about 8,000 miles, right?  And that’s pretty far short of 100 million miles.

Well, not exactly.  Because Earth is moving.  In six months time you will be 186 million miles away from where you are right now, round the other side of the Sun.

That’s a pretty long exposure photograph, I know, but to get the maximum resolution of deep-space objects, this is exactly what astronomers do.  We use the motion of our own planet in orbit to get an effective telescope diameter the same size as the diameter of our orbit.  Which is pretty mindblowing to me.

Now, this is currently only really used for radio frequencies, but I would expect it’s not impossible to use a similar system for visible frequencies.  Not that it would be much use for identifying features on a planet, as that planet will likely also be spinning on an axis and certainly it will be orbiting a star, and because its orbit would need to be in a fairly narrow range of distances away from that star for it to be habitable, its orbit would be of roughly the same order as our own (a few months to a few years), so over a 6 month exposure that planet will be a blur, but still, we could at least see that it’s there.  From the way its atmosphere reflects and transmits light we could detect possible signs of industry.  We could make informed guesses about oceans and landmasses.  We could even potentially detect signs of life.

And all of that makes me pretty damn excited.

The Ultimate Telescope