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A Telescope The Size Of The Earth
Neil Blender writes "From this article: "Astronomers have fashioned an Earth-sized virtual radio telescope that can distinguish celestial features 3,000 times smaller than the those observed by the Hubble Space Telescope. The device, which uses atomic clocks and a custom supercomputer to link together radio dishes on three continents, is the most powerful radio observatory ever, according to scientists." Some parts of the custom supercomputer use linux and IDE RAID."
While I don't doubt the value a radio telescope might have for planetary research, I'm willing to bet you're thinking about something akin to being able to see the individual cells on Pathfinder's solar-array on the surface of Mars from a telescope mounted here on Earth.
Anyone know the _optical_ resolution for maximum "zoom" on Hubble...?
A really good telescope will usually be limited by diffraction effects (the fact that the telescope is of finite size causes light being focused to blur out a bit as it passes through the telescope aperture).
A back of the envelope calculation suggests that the diffraction-limited resolution of the Hubble (at 2.5m) for 500 nm light is about 0.2 microradians (letting it resolve features ten million kilometres wide at Alpha Centauri, five light-years away [give or take], or letting you read a typewritten letter at 5 km).
A radio telescope typically operates on wavelengths on the order of a tenth of a metre (as a gross approximation; it's really an order of magnitude in either direction from there, if I understand correctly). The largest radio telescope dish on the planet is about 300m wide, giving a diffraction-limited resolution of about 0.3 milliradians, or about three times sharper than the unaided human eye is at optical wavelengths (the equivalent of reading a typewritten letter at about 10 feet).
An interferometric radio telescope with an aperture the size of the planet would have a resolution of about 10 nanoradians, letting it resolve features about 0.5 million kilometres wide at Alpha Centauri [slightly smaller than our sun] (the equivalent of reading a typewritten letter at a distance of 100 km, or the title on a paperback book from low Earth orbit).
If we had a radio telescope with an atomic clock on the moon (about 400,000 km away), we could resolve objects the size of Jupiter in the Alpha Centauri system. If we had a space-based radio telescopes in the Earth-Sun L4 or L5 points (each 150 million km from Earth), we could resolve individual cities on an Earth-like planet.
This is cheap enough to do that we're probably going to put radio telescopes there within the next couple of decades. Any planet with a magnetosphere within 50-200 light years would be detectable, and we'd have detailed maps of magnetic effects on the surfaces of every star within a thousand light-years.