The RATAN-600 (russian: РАТАН-600 – радиоастрономический телескоп Академии наук – 600, an acronym for the " Academy of Sciences Radio Telescope – 600") is a

radio telescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency ...

in Zelenchukskaya, Karachay–Cherkess Republic,

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

. It comprises a 576 m diameter circle of rectangular radio reflectors and a set of secondary reflectors and receivers, based at an altitude of 970 m. Each of the 895 2×7.4 m reflectors can be angled to reflect incoming radio waves towards a central

conical A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines c ...

secondary mirror, or to one of five parabolic cylinders. Each secondary reflector is combined with an instrumentation cabin containing various receivers and instruments. The overall effect is that of a partially steerable antenna with a maximum resolving power of a nearly 600 m diameter dish, when using the central conical receiver, making it the world's largest-diameter individual radio telescope.

Operating modes

The telescope can operate in three modes: * Two-mirror system: A sector of the ring focuses waves to the cylindrical secondary mirror which directs them onto the receivers. * Three-mirror system: The linear plane mirror reflects the waves to the south sector of the ring, which focuses them on a cylindrical secondary, that reflects them onto the receivers. This is a Kraus-type periscope mirror system. * Entire ring: For observations near the zenith, the entire ring can be used, together with the conical secondary mirror and its receivers. Simultaneous independent observations at various discrete azimuths are possible. For this, a sector of the ring is coupled with one of the secondary mirror-and-receiver units, which can be positioned using railway tracks, while another sector, in conjunction with another secondary mirror, is similarly used for an independent observation.

Optical specifications

It has a resolving power in the horizontal plane of 1 arcminute at a

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 ...

of 8 cm (3.75 GHz). The effective collecting area of the entire ring is which is 0.33% of that expected of a completely filled reflector of this size.

Transit telescope

The RATAN-600 is primarily operated as a

transit telescope In astronomy, a transit instrument is a small telescope with extremely precisely graduated mount used for the precise observation of star positions. They were previously widely used in astronomical observatories and naval observatories to meas ...

, in which the rotation of the Earth is used to sweep the telescope focus across the subject of observation.

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 up ...

observations can be made in the frequency band 610 MHz to 30 GHz, though primarily in the centimetric waveband, with an angular resolution of up to 2 arcseconds. Observation of the Sun at radio wavelengths, in particular of the

solar corona A corona ( coronas or coronae) is the outermost layer of a star's atmosphere. It consists of plasma. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. It is most easily seen during a total solar ...

, has been a long-standing focus of the RATAN-600's scientific programme. It has also contributed to radio observation for the

SETI The search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other pl ...

project. The RATAN-600 has not suffered from the persistent technical problems of the neighbouring

BTA-6 The BTA-6 (russian: Большой Телескоп Альт-азимутальный, translit=Bolshoi Teleskop Alt-azimutalnyi, translation=Large Altazimuth Telescope) is a aperture optical telescope at the Special Astrophysical Observatory lo ...

, and has generally been in high demand since it began operation in mid-1974.

SETI candidate signal

On 15 May 2015, at 18:01:15.65

sidereal time Sidereal time (as a unit also sidereal day or sidereal rotation period) (sidereal ) is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coor ...

, RATAN-600 detected a strong (0.75 Jansky) signal from the direction of

HD164595 HD 164595 is a G-type star located in the constellation of Hercules, from Earth that is notably similar to the Sun. With an apparent magnitude of 7.075, the star can be found with binoculars or a small telescope in the constella ...

. More specifically, the signal intensity rose and fell as the telescope panned past in a way that closely matched what would be expected for a distant source. Since the short wavelength (2.7 cm, or 11 GHz, in the

X band The X band is the designation for a band of frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is rather indefinitely set at approxi ...

) is unusual for a natural source of that power, after the researchers announced the signal in late August 2016 (in the form of a request for follow-up observations) there was a flurry of excitement that it might be a

candidate. Of course, the same artificial appearance also makes a terrestrial source likely. Because the signal is in a frequency band allocated to military use, it might have originated from a secret

reconnaissance satellite A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications. Th ...

. After further analysis, and a failure of other observatories to corroborate the signal, the Special Astrophysical Observatory concluded that it was of probably terrestrial origin. Later research suggests that it might have been a faulty satellite in a slow spin, as the frequency matches one used for inter-satellite beacons, but was more likely to be the downlink from an intact but classified satellite.

Gallery

File:RATAN 600.jpg, Photo of the RATAN-600 in its environment File:Feed cabin 1 of Ratan-600, SAO RAS.jpg, One of the conical secondary reflectors of the RATAN-600 File:Dmitry Cherasov and Ratan-600.jpg, Reflector plates, measuring 11,4 m × 2,0 m

References