# Talk:Astronomical interferometer

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## Reading a license plate on an extrasolar planet?

Could someone discuss the technical requirements of making a Really Good Telescope - i.e. one that can be used to view fine detail of life around another star? My untutored logic finds that if the angular resolution is approximately 1.220 lambda/D arc seconds (so the Hubble Space Telescope gets 0.05 arcseconds for a 2.5 meter mirror for example), with 4.85 x 10E-6 radians per arcsecond, the Hubble should resolve one astronomical unit at 30 light years. But there are 149,597,870,691 meters in an astronomical unit, so it should take roughly a 30 km mirror (spacing) to resolve opposite ends of a planet. As far as I know the largest that the mirrors can be spaced is the orbit of Neptune (since it clears a path in its orbit), 60 AU apart. This gives roughly a 0.5 inch resolving power, which might be good enough to read a license plate depending on how tall the aliens are. ;) But how large each mirror needs to be is another question, as is how many you need to be able to point the array at a fair proportion of extrasolar planets. Of course, all this is "WP:original research" and not a very good example of that, but I wanted to clarify what I'd hope to see an expert try to illustrate for the article. Wnt (talk) 17:56, 27 January 2008 (UTC)

I myself have been curious about the limits of hypertelescopes, wondering if solar system wide or larger arrays could be built in interstellar or even (slightly) intergalactic space, far away from solar wind interference with construction times of hundreds of thousands if not millions of years. Michio Kaku, Frank Tipler, and Ray Kurzweil have all written about the eventual expansion of life (likely in the form of AI with advanced nanotech) throughout the universe and it would follow that should advanced civilizations want to observe essentially everything that can be observed, such structures would be built. With resolutions of pico and femtoarcseconds, even hypervelocity intergalactic exoplanets could be identified, imaged, and cataloged, with Von Neumann probes dispatched to colonize upon arrival a few million years later. In some cases the imaging might take so many millennia, it could be faster to send the probes blind and transmit the specifics of the destination en route with minor course corrections implemented. Unless there are technical reasons why hypertelescopes can't be above a certain size, then the Matrioshka/Jupiter brains that will come to rule the universe will build them in addition to all sorts of staggering megaengineering projects. — Preceding unsigned comment added by 70.194.81.218 (talk) 00:59, 16 December 2014 (UTC)

## How? Why?

How does an interferometer provide better resolution than a single telescope? Are we allowed to have a single sentence explanation in the introduction of this article?

In the drawing of two telescopes side by side there is no explanation of what the two setups provide beyond a single telescope. Why an interferometer? I imagine some utility such as parallax estimations of distances or various other possibilities but why doesn't the article say it? Rtdrury (talk) 08:49, 13 March 2008 (UTC)

The benefit of the interferometer is that the angular resolution of the instrument is nearly that of a telescope with the same aperture as a single large instrument encompassing all of the individual sub-components. (See Rayleigh criterion.) The drawback is that it does not collect as many photons as a large instrument of that size. Thus it is mostly useful for fine resolution of brighter objects. Regards, RJH (talk) 15:10, 10 March 2012 (UTC)

## Bad figure

The correct focus is a lot closer to the parabola, resulting in equal optical path lengths for all incoming parallel rays.

The article's introductory figure File:Interf diagram.gif is spectacularly bad: the crucial principle of an interferometer, equal optical path length to the combiner, is not apparent and in fact appears to be violated. The reason is that the focus is drawn at a wrong location; it should be much closer to the parabola. AxelBoldt (talk) 23:07, 1 February 2014 (UTC)

I agree, so I've removed the image. Thanks! Stigmatella aurantiaca (talk) 23:42, 1 February 2014 (UTC)

## Is this primarily about optical interferometry

Seems to be - so should we be explicit in the lead and have hatnotes to radio interferometry (redirects to Radio_telescope#Radio_interferometry and also covered in Radio_astronomy#Radio_interferometry) ? - Rod57 (talk) 13:07, 22 July 2016 (UTC)

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