Astronomical interferometer

Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.

One simple layout of an astronomical interferometer is a parabolic arrangement of mirror pieces, giving a partially complete reflecting telescope but with a "sparse" or "dilute" aperture.

One of the first uses of optical interferometry was applied by the Michelson stellar interferometer on the Mount Wilson Observatory's reflector telescope to measure the diameters of stars.

Software packages such as BSMEM or MIRA are used to convert the measured visibility amplitudes and closure phases into astronomical images.

A number of other interferometers have made closure phase measurements and are expected to produce their first images soon, including the VLTI, the CHARA array and Le Coroller and Dejonghe's Hypertelescope prototype.

Additional results include direct measurements of the sizes of and distances to Cepheid variable stars, and young stellar objects.

High on the Chajnantor plateau in the Chilean Andes, the European Southern Observatory (ESO), together with its international partners, is building ALMA, which will gather radiation from some of the coldest objects in the Universe.

ALMA will be a single telescope of a new design, composed initially of 66 high-precision antennas and operating at wavelengths of 0.3 to 9.6 mm.

The antennas can be spread across the desert plateau over distances from 150 metres to 16 kilometres, which will give ALMA a powerful variable "zoom".

It is often said that an interferometer achieves the effect of a telescope the size of the distance between the apertures; this is only true in the limited sense of angular resolution.

The amount of light gathered—and hence the dimmest object that can be seen—depends on the real aperture size, so an interferometer would offer little improvement as the image is dim (the thinned-array curse).

However, they have proven useful for making very high precision measurements of simple stellar parameters such as size and position (astrometry), for imaging the nearest giant stars and probing the cores of nearby active galaxies.

Max Tegmark and Matias Zaldarriaga have proposed the Fast Fourier Transform Telescope which would rely on extensive computer power rather than standard lenses and mirrors.

ESO 's VLT interferometer took the first detailed image of a disc around a young star. [ 2 ]
A 20-foot Michelson interferometer mounted on the frame of the 100-inch Hooker Telescope , 1920.
Aerial view of the ESO /NAOJ/NRAO ALMA construction site.
The Navy Precision Optical Interferometer (NPOI) , a 437 ma baselined optical/near-infrared, 6-beam Michelson Interferometer at 2163 m elevation on Anderson Mesa in Northern Arizona, USA. Four additional 1.8-meter telescopes are being installed starting from 2013.
Light collected by three ESO VLT auxiliary telescopes, and combined using the technique of interferometry.
This image shows one of a series of sophisticated optical and mechanical systems called star separators for the Very Large Telescope Interferometer (VLTI). [ 13 ]
Two of the Atacama Large Millimeter/submillimeter array ( ALMA ) 12-metre antennas gaze at the sky at the observatory's Array Operations Site (AOS), high on the Chajnantor plateau at an altitude of 5000 metres in the Chilean Andes.