A series of nine American lunar probes, launched between 1961 and 1965. Only the last three, Rangers 7, 8 and 9, were successful. Ranger 7, launched in July 1964, returned 4,000 images. Thousands more were obtained with Rangers 8 and 9, launched in February and March 1965. They were hard landers, designed to transmit images during approach to the Moon until they crash-landed. The three successful Rangers landed successively in the Fra Mauro region, the Mare Tranquillitatis and the crater Alphonsus.

Abbreviation for Royal Astronomical Society.

The brightest star in the constellation Hercules. It is a binary, consisting of a red supergiant M star with a sixth magnitude companion of spectral type F, which appears greenish in contrast. The secondary is itself a spectroscopic binary. The primary star is an irregular variable, its magnitude ranging between 3 and 4. The name, of Arabic origin, means the kneeler’s head.

A radio telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences, located at Zelenchukskaya in the Caucasus Mountains. The name is an acronym derived from radio astronomy telescope of the Academy of Sciences in Russian. It consists of 900 parabolic plates forming a circle 600 metres 2,000 feet in diameter. It can be used as a whole, or each quarter can operate as a self-contained unit.

A light-coloured, linear feature extending radially from a crater. A number of lunar craters are surrounded by extensive and conspicuous ray systems that show up particularly at full Moon, when they can be seen with the unaided eye. Ray systems are associated with the youngest craters, such as Tycho and Copernicus. They may be due to rock surfaces exposed in relatively recent impacts; such surfaces would be more reflective than old surfaces that have been subjected to radiation for millions of years. Alternatively, rays may consist of glassy, reflective ejecta. Rays are also found around craters on several other bodies in the solar system.

decoupling era.

A spectral feature produced by electromagnetic radiation at a particular wavelength emitted when an electron in an ionized gas is captured by a positive ion. Energy is released in the form of photons corresponding to discrete wavelengths as the electron drops through the energy levels of the atom.

A nova known to have had two or more outbursts. The interval between outbursts typically ranges between 10 and 80 years. It is possible that all novae are recurrent and that only the ones with the shortest periods are recognized. However, the known recurrent novae differ from classical novae in that their amplitudes of six to eight magnitudes are smaller, and their spectra during outbursts are different. At other times their spectra seem to indicate the presence of a red giant in the system.

An evolved star that has greatly expanded in size and undergone a change in its surface temperature so that it appears red. A star becomes a red giant at a phase in the course of stellar evolution where the hydrogen fuel for nuclear fusion in the central core has been exhausted. In the internal adjustment that follows, the core collapses until sufficient gravitational energy is released to cause hydrogen burning to restart, but in a shell around the now inert core. The energy generated by shell burning of hydrogen causes the great expansion of the star’s outer layers. As the gas expands, it cools. Regardless of the star’s original spectral type, its surface temperature drops until it reaches 4,000 K. When the Sun becomes a red giant, it will expand until its diameter is roughly the diameter of the Earth’s orbit. Though the light emitted per unit surface area of a star decreases sharply with temperature, a red giant compensates for this effect by the enormous increase in surface area. Thus, red giant stars are relatively very luminous. All the bright red stars visible to the naked eye are giants or supergiants, such as Aldebaran or Betelgeuse. The spectra of red giants show different characteristics according to whether the stellar atmosphere is rich in carbon or oxygen. If oxygen is dominant, carbon monoxide CO and metallic oxides, such as titanium oxide TiO are evident. If carbon predominates, carbon compounds such as C2, CH and CN are formed; such giants are called carbon stars. The different compositions observed in red giants are presumed to be the result of processes that bring to the surface the products of nuclear reactions that have taken place in the interior.

A popular name for the planet Mars, which has a distinctly reddish hue even to the naked eye.

A red nebula around the star HD 44179, detected in 1975 during a survey of infrared sources. The emission, which is intrinsic to the nebula and not scattered or reflected light, is in a broad band in the red part of the spectrum, peaking at about 640 nanometres. It is the strongest known source of this red emission, which may be a result of luminescence from hydrogenated amorphous carbon dust.

Great Red Spot.

A change in the distribution of continuum electromagnetic radiation from a source such that the intensity at longer wavelengths is enhanced and that at shorter wavelengths diminished. Reddening occurs when light travels through the interstellar medium. See also: interstellar reddening.

The increase in wavelength of electromagnetic radiation caused either by the Doppler effect, when the source of radiation is moving away from the observer, or by the presence of a gravitational field. It is quantified in terms of the wavelength change Δλ expressed as a fraction of the rest wavelength l measured when the source and observer are not in relative motion: z = Δλ/λ. The theory of the Doppler effect gives the relationship between redshift arising from relative motion and the relative velocity of the source and observer. The redshifts of galaxies and quasars are particularly important in astronomy since, through Hubble’s Law, they are generally regarded as direct indicators of the distances to these objects. In General Relativity, Einstein also predicted that there would be a redshift effect in the presence of a strong gravitational field.

A telescope in which the main light-collecting element is a mirror.