Alternative name for P Cygni star. S Doradus itself is an irregular variable star in the Large Magellanic Cloud, and is currently eleventh magnitude. It has a very high mass, estimated to be about 60 times the mass of the Sun, and is as luminous as a powerful nova.

A cool giant star of basic spectral type K or M, which shows in its spectrum distinct absorption bands of the molecule zirconium oxide ZrO. S stars also often have bands of lanthanum oxide LaO, yttrium oxide YO and vanadium oxide VO. In normal M stars, the most prominent molecular bands are those of titanium oxide TiO. The dominance of ZrO in S-type stars reflects a higher ratio of carbon to oxygen and a high abundance of zirconium. The zirconium and other heavier elements are the products of nuclear reactions in the star’s interior which have been brought up to the surface.

A process of nucleosynthesis in which heavy elements are created from light ones by the successive capture of neutrons. The s stands for slow. In the s-process there is time for a newly formed nucleus to decay by the emission of an electron beta decay before another neutron is captured, in contrast with rapid neutron capture - the r-process - in which this is not the case. The s-process is believed to occur within stars of less than 9 solar masses during the red giant phase of evolution. Some isotopes of heavier elements can be formed only by the s-process, and their abundance in the solar system is strong evidence that the s-process was responsible. These elements were created in a generation of stars that existed prior to the formation of the solar system. When those sufficiently massive to do so exploded as supernovae, they enriched the interstellar material with the products of nuclear processes from their interiors.

A category of asteroid of intermediate albedo, thought to be made of silicaceous material, similar to stony meteorites. S-type asteroids are relatively common in the inner asteroid belt.

Anisotropy in the cosmic background radiation caused by the gravitational field of large-scale structure in the universe.

A solar observatory in New Mexico, forming part of the facilities of the US National Solar Observatory. The observatory site, known as Sunspot, is in the Lincoln National Forest at a height of 2,800 metres 9,200 feet. It was founded in 1951 as the Upper Air Research Observatory of the Air Force Cambridge Research Laboratories to predict disturbances to, for example, communications, caused by solar activity. In 1976, the observatory was transferred to the National Science Foundation and, in 1984, it became part of the National Solar Observatory section of the National Optical Astronomy Observatories. The largest instrument is a vacuum tower telescope. It is used to observe small-scale solar features and has a resolving power better than a quarter of an arc second. The John W. Evans Solar Facility named after the first director contains various instruments including a 40-centimetre 16-inch coronagraph and a 30-centimetre 12-inch coelostat, which can feed solar radiation to several instruments.

The third-smallest constellation, but nevertheless a rather distinctive little group of stars, included in the 48 constellations listed by Ptolemy c. AD 140. The two brightest stars are third magnitude. It lies in a rich part of the Milky Way, next to Aquila.

The southernmost constellation of the zodiac, and one of those listed by Ptolemy c. AD 140. The centre of the Galaxy the Milky Way lies behind the star clouds in Sagittarius. It is a large constellation, with many bright stars; there are 14 brighter than fourth magnitude. It also contains a large number of star clusters and diffuse nebulae. The Messier Catalogue lists 15 objects in Sagittarius, more than in any other individual constellation. They include the Lagoon Nebula, the Trifid Nebula, the Omega Nebula and the third-brightest globular cluster in the sky, M22.

The overall name for the complex radio source associated with the galactic centre. It is composed of at least four separate sources, known as Sagittarius A, B, B2 and C. A bright, compact source known as Sagittarius A* is believed to be the closest to the actual centre of the Galaxy.

One of the spiral arms of the Galaxy. It lies between the Sun and the centre of the Galaxy in the direction of the constellation Sagittarius.

sagittarius A.

A set of mathematical expressions, formulated in 1920 by the Indian physicist Megh Nad Saha, from which can be calculated the numbers of atoms in each of the possible ionization states for atoms and electrons in thermodynamic equilibrium at a particular temperature. They are important in interpreting stellar spectra and the conditions in stellar atmospheres.

English name for the constellation Vela.

A simple theoretical expression, named after the theorist Edwin Salpeter b. 1924, for the numbers of stars of different masses among newly formed stars per unit volume of a galaxy. The Salpeter function, also known as the initial mass function, is proportional to M to the power of -2.35 where M is the mass of a star.

An alternative name for the triple-alpha process.