Page last updated at 14:12 GMT, Tuesday, 17 November 2009

Alma antennas collect first data

Alma antennas on Chajnantor (ESO)
The first two Alma antennas have been linked up as an "interferometer"

A team working on the Alma observatory in Chile have made their first measurements from the telescope's site, located 5,000m up in the Andes.

Astronomers and engineers took their first "interferometric" measurements of radio signals - so-called "fringes" - of an astronomical source.

This is an important technical step for the Alma project.

The antennas were moved into position at the observatory site on Chajnantor plateau in Chile on 16 and 17 October.

In radio astronomy, interferometry involves linking together arrays of smaller telescopes to make measurements of an object.

The Atacama Large Millimeter/submillimeter Array (Alma), involves partners from Europe, North America and East Asia in co-operation with Chile.

Those behind the project say the observatory represents a revolutionary new design and concept for radio astronomy.

Currently under construction on Chajnantor plateau, in the thin, dry air of northern Chile's Atacama desert, the telescope array will consist of 66 high-precision antennas.

These are designed to work together, observing the sky at millimeter and submillimeter wavelengths.

Thanks to its high resolution and sensitivity, Alma will open a new "window" on the Universe, according to astronomers.

It should be able to observe some of the first galaxies to form after the Big Bang, and catch planets in the act of forming around young stars.

This will allow scientists to unravel longstanding and important puzzles about the Universe.

The latest technical step forward involved two of the array's 12m-diameter antennas, and sophisticated electronic systems for receiving and correlating the signals.

This is the first time all these items have been used together as a complete system.

"Fringes" are seen when signals received by a pair of antennas are combined with exactly the right timing. The collection of this data represents a first step towards making detailed images of the astronomical objects being observed.

Astronomers said the measurement of fringes from the quasar 3C454.3 at a wavelength of less than 1mm showed Alma was now truly a "submillimetre" as well as millimetre-wave telescope.

The next step in the process will be the addition of a third antenna which will allow the Alma team to obtain "phase closure".

This is an important capability which requires at least three antennas to cancel out errors in the "phase" of the signals caused by the instruments themselves and by the Earth's atmosphere.

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