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harsh mehta Grade: 12

Please explain what is astronomical interferometry?

8 years ago

Answers : (1)

shashank Saxena
13 Points

Astronomical Interferometry

The angular resolution that a telescope can achieve is determined by its diffraction limit (which is proportional to its diameter). The larger the telescope, the better its resolution. However, the cost of building a telescope also scales with its size. The purpose of astronomical interferometry is to achieve high-resolution observations using a cost-effective cluster of comparatively small telescopes rather than a single very expensive monolithic telescope. The basic unit of an astronomical interferometry is a pair of telescopes. Each pair of telescopes is a basic interferometer. Their position in u,v space is referred to as a baseline.

Early astronomical interferometry was involved with a single baseline being used to measure the amount of power on a particular small angular scale. Later astronomical interferometers were telescope arrays consisting of a set of telescopes, usually identical, arranged in a pattern on the ground. A limited number of baselines will result in insufficient coverage in u,v space. This can be alleviated by using the rotation of the Earth to rotate the array relative to the sky. This causes the points in u,v space that each baseline points at to change with time. Thus, a single baseline can measure information along a track in u,v space just by taking repeated measurements. This technique is called Earth-rotation synthesis. It is even possible to have a baseline of tens, hundreds, or even thousands of kilometers by using a technique called very long baseline interferometry.

The longer the wavelength of incoming radiation, the easier it is to measure its phase information. For this reason, early imaging interferometry was almost exclusively done with long wavelength radio telescopes. Examples of radio interferometers include the VLA and MERLIN. As the speed of correlators and associated technologies have improved, the minimum radiation wavelength observable by interferometry has decreased. There have been several submillimeter interferometers, with the largest, the Atacama Large Millimeter Array, currently under construction. Optical astronomical interferometers have traditionally been specialized instruments, but recent developments have broadened their capabilities.

8 years ago
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