Prototype Telescopes Complete Key Test

Matthew Sparkes writes "Two prototype antennas for the world's largest array of millimeter-wave telescopes have passed a key test, working to track and image Saturn for more than an hour. Ultimately, ALMA (Atacama Large Millimeter/submillimeter Array) is expected to resolve details 10 times finer than the Hubble Space Telescope when it is completed in 2012."

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[Anonymous Coward]

Two prototype antennas for the world's largest array of millimetre-wave telescopes have passed a key test, working together to track and image Saturn for more than an hour on 2 March. Ultimately, ALMA (Atacama Large Millimeter/submillimeter Array) is expected to resolve details 10 times finer than the Hubble Space Telescope when it is completed in 2012.
ALMA will use up to 64 antennas and will be located in the Atacama desert, 5 kilometres above sea level in the Chilean Andes. Designed to look through dust clouds to reveal star formation, image embryonic planets and probe the early universe, it will be the world's most sensitive telescope at wavelengths of 0.3 to 9.6 millimetres - a regime obscured at lower altitudes by atmospheric moisture.
But making all of the 12-metre dishes function like a single giant telescope will be a challenge. Fibre-optic cables will link each dish to every other dish in the array, and to a giant special-purpose electronic computer called a correlator.
"It collects the amplitude and phase information from each of the antennas, and knowing their distances from each other, it lines everything up to produce a coherent picture of the source," says Jeff Mangum, an ALMA project scientist at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, US.
'Fringes of the universe'
The 2 March test actually linked two prototype antennas at another observatory, the Very Large Array site in New Mexico, US, with each other and with a small-scale prototype of the correlator. But the test, called 'first fringes', bodes well for ALMA's future, Mangum told New Scientist: "It verifies that ALMA can make measurements not just as single telescopes, but as a collection of antennas, which is the primary mode of operation."
Millimetre waves are at the upper end of the radio spectrum, just below infrared radiation. They can reveal important organic molecules, but are obscured by atmospheric moisture.
Small arrays at lower elevations have probed the sky since the 1980s, but atmospheric moisture made observations difficult at wavelengths shorter than 3 millimetres. A 1990 report urged building a large array at high elevation, and the NRAO, the European Southern Observatory, and the National Astronomical Observatory of Japan later picked the Atacama site. The altitude puts the array above most of our atmosphere's water, allowing observations down to 0.3 millimetres.
Although plans call for up to 64 antennas, present funding can pay for only 50 or so dishes. The dishes will be movable, allowing baselines from 150 metres to 18 kilometres, with the longest baseline and the shortest wavelength giving resolution as fine as 0.005 arcsecond, a factor of 10 better than Hubble.
Because millimeter waves can penetrate dust that blocks visible light, ALMA's large collecting area "will make it much easier to detect very faint objects at the fringes of the universe", says Mangum.

More embargo than censorship.

[jpellino]

Hubble releases public images, but much of the research is just that - research - done by labs who are trying to maintain the integrity and proprietary nature of their work. Hubble data is supposed to go to the researcher first and the public second. IIRC it's a default six month delay unless overridden by the lab collecting the data. It's not censorship so much as embargo, and it's really no different from what any researcher does in order to not be scooped on the research they're doing.

Re:the use of space-telescopes?

[Nyeerrmm]

The idea of using interferometry is really interesting. The idea of an earth sized telescope is great. In fact, in Texas there is an attempt to build a Texas-sized interferometer with amplitude interferometer based on the Hanbury-Brown-Twiss effect. Basically the goal is to have universities or other entities across the state erect their own telescopes (we're using 16-inchers) which they will own and operate on their own, and then have a network set up where anyone can take over and run them. Hopefully we'll get the first two up soon.

For those that don't know, the method we're using, amplitude interferometry has a number of advantages. Compared to amplitude interferometer, it is easy to set up on long distances, since it doesn't require micrometer precise spacing and direct optical links. It also has better signal-to-noise qualities than a heterodyne interferometer, because those are dominated by Heisenburg effects. Finally, one of the really nice things (although we're not taking advantage of it) is that it doesn't require optical quality telescopes and good CCDs, all it requires is light collectors and good quality photodetectors., a data connection, and some voodoo math. This makes it relatively cheap, even if you have to go into space to do the observing. A 15-meter telescope in orbit is an impossibility right now, but a 15-m light collector, deployed as an inflatable foil structure has a lot of promise.

Re:Apples and oranges

[jcorno]

Except that one is a radio telescope and one is an optical telescope.

So what? Stars and other black bodies radiate in both visible and microwave. If you're trying to resolve nearby objects (like binary stars or planetary systems), either one will work. Resolution is resolution. And besides, the angle resolved by a telescope is proportional to wavelength, so that just makes it MORE impressive. This telescope has a better resolution than the Hubble, even though it's working with 1000 times the wavelength.

Re:More embargo than censorship.

[Greg Lindahl]

The astronomy community does exactly what you're asking for, you're just not listening:

* The data is made available to everyone after a short time delay

* The software to reduce the data is given away for free

* Our papers are generally available for free at http://lanl.arxiv.org/ [arxiv.org]

The point of the short delay is that the person who made the effort to write the proposal to get the telescope time deserves a reward: a short time to write the first paper about the results.

If you look at other branches of science, they aren't nearly as good. But you're flaming your friends.