Chart Showing Radio Signal of First Identified Pulsar

The Interplanetary Scintillation Array (also known as the IPS Array or Pulsar Array) is a radio telescope that was built in 1967 at the Mullard Radio Astronomy Observatory, in

Cambridge, United Kingdom Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge became ...

, and was operated by the

Cavendish Astrophysics Group The Cavendish Astrophysics Group (formerly the Radio Astronomy Group) is based at the Cavendish Laboratory at the University of Cambridge. The group operates all of the telescopes at the Mullard Radio Astronomy Observatory except for the 32m MERL ...

. The instrument originally covered 4

acre The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, of a square mile, 4,840 square ...

s (16,000 m²). It was enlarged to 9 acres in 1978, and was refurbished in 1989. The array operates at a

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the uppe ...

of 81.5 MHz (3.7 m

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...

), and is made up of 4,096

dipole antenna In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole w ...

s in a

phased array In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving t ...

. Using 14 beams, it can map the northern sky in one day. The observatory's staff use

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated sh ...

to keep grass away from the antennas because a

lawn mower A lawn mower (also known as a mower, grass cutter or lawnmower) is a device utilizing one or more revolving blades (or a reel) to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, but g ...

cannot fit in the spaces. Antony Hewish designed the IPS Array to measure the high-frequency fluctuations of radio sources, originally for monitoring interplanetary scintillation. Hewish received a

Nobel prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfre ...

after the high time-resolution of the array allowed the detection of

pulsars A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

by Jocelyn Bell in 1967. The IPS Array has more recently been used to track and help forecast interplanetary weather, and specifically to monitor the solar wind. It is now essentially retired, and has lost a significant fraction of its area.

References

Cavendish Laboratory Radio telescopes {{observatory-stub