By: Wolf Lange
A selective mixture of interesting terminology, objects, people of interest to all that love and are involved in Astronomy. Compiled by Wolf Lange who will deny any wilful exclusions . . . . . . . . . . . . .
Sources include: Collins Dictionary of Astronomy 2nd Edition, Burnhams Celestial Handbook Revised and Enlarged Edition, Patterns in the Sky by Julian DW Staal and the Amateur Astronomers Handbook by JB Sedgwick.
Baileys Beads – a string of brilliant points of sunlight sometimes seen, very briefly, at the moon’s edge just before or after totality in a solar eclipse. They are the result of sunlight shining through the valleys on the moon’s limb as the sun disappears or emerges from behind the moon. (Great for astrophotography!)
Barlow lens – an achromatic (see under A in previous issue) diverging lens placed between the eyepiece of a telescope and the secondary mirror in order to increase the effective focal length of the primary mirror – this in turn increases the magnification (at the cost of loss of some light).
Beta Centauri (b ?Cen, Hadar, Agena). A luminous remote but still conspicuous bluish-white giant that is the second brightest star in the constellation Centaurus. (See also a Cen or Alpha Centauri). Spectral type B 1 II at a distance of 100pc.
Betelgeuse (a Ori) – pronounced "beetlejuice" or also Bet el jooze; its meaning comes directly from the Arabic: "The keeper of the twins" (referring to Gemini) – sort of a "shepherd" of the twins. A remote luminous red supergiant that is the second brightest star in the constellation of ORION. It is also a semiregular variable with a period of 5.8 years ranging in magnitude from 0.3 to 0.9. According to IRAS it’s a strong source of infrared radiation which is emitted from three concentric shells the largest of which is 1.5 parsecs, ejected within the past 100 000 years. Spectral type M2 Iab; with a diameter of 500x solar at a distance of 150parsecs.
Big Bang Theory – a cosmological model in which all matter and radiation in the universe originated in an explosion at a finite time in the past. Another theory is that of the Inflationary universe (see later on in this series). The Big Bang theory has been remarkably successful in explaining the expansion of the universe, the background radiation and the cosmic abundance of helium.
George Gamow in the 1940s suggested a hot Big Bang in which the temperature of matter and radiation decreases with time. This was verified by the discovery of the cosmic microwave background in 1965. It is estimated that the universe came into existence some 10 to 20 billion years ago (10 000 to 20 000 million).
See also some related topics later in this series covering Neutrinos, Quarks, Redshift, Planck Time and Microwave background radiation.
Big Dipper (Brit. Plough) – a group of stars in Ursa Major (Big Bear) that contains the seven brightest stars in that constellation, nearly all with similar magnitudes! In order of brightness these are: Alioth, Dubhe, Alcaid, Mizar, Merak, Phecda and Megrez. Very interestingly the shape of the Big Dipper is slowly change because of the stars Alcaid and Dubhe having different values and direction of Proper Motion than the other 5 (the apparent angular motion per year of a star on the celestial sphere i.e. in a direction perpendicular to the line of sight – resulting from both the actual movement of the star in space and the star's motion relative to the solar system).
Black Hole – simplistically described as "an object so collapsed that its escape velocity exceeds the speed of light". (Earth’s escape velocity is 11.2km s-1 = +/- 26 000km/hour and the speed of light 299 792 458 m s-1 a value adopted by the IAU in 1975.)
It becomes a black hole when its radius has shrunk to its Schwarzschild radius: Rs = 2GM/c2 where G is the gravitational constant and c the speed of light e.g. for our sun the radius would be three km.
Light cannot escape. The event horizon marks the boundary inside of which all information is trapped. Space and time become highly distorted inside the event horizon.
The most promising candidates for black holes are massive stars that explode as Supernovae leaving a core in excess of 3 solar masses. See also White Dwarfs and Neutron stars later on .
Blue shift – an overall shift of the spectral lines in a spectrum towards shorter wavelength as a result of the Doppler effect. It is observed in spectra of celestial objects approaching earth. (If the object is large enough and indicates a shift to blue -– i.e. a fearful chill may also be bserved in humans observing such an object approaching at speed!)
Bok globules – small dark cool (10K) clouds of gas and dust seen as near circular objects against the background of stars or of an H II region. Named after Dutch-American astronomer Bart J Bok. (NOT what you first thought they were! What is it in Afrikaans?)
Bolide – a brilliant METEOR that appears to explode, i.e. a detonating fireball. (This author has seen at least three). The brighter ones are caused by ablating Meteorites (= loss of material from the surface as a result of vaporisation, friction etc) that subsequently fall to earth. About 500 bolides are observed each year.
Brightest stars – there are approx 9 500 stars brighter than the visual magnitude of 6.5. Brightness may be the result of being close to earth, being very bright or both. The most luminous lie in the supergiant and giant regions of the Hertzprung-Russell diagram (and not in the vicinity of Hollywood).
Brown dwarf – a theoretical star formed by the contraction of a lump of gas with a mass too small for nuclear reactions to begin in the core. This sad state of affairs results in an object "glowing" for about 100 million years before cooling off. The first brown dwarf, named Gliese 229B, was unambiguously identified in 1995 with the Palormar 60 inch telescope. It orbits the red dwarf star Gliese 229A. One spectrum signature unique to brown dwarfs is the presence of methane lines. The stellar mass limit is perceived to be in the region of 0.08 solar masses. Perhaps our two giant planets could have been "near" candidates to becoming brown dwarfs?
B-type Asteroids –see C-type asteroids!
Butterfly diagram – a diagram representing the distribution of sunspots on both sides of the sun’s equator over a long time period of about 100 years, will show high density between 35 degrees north and 35 degrees south in the shape of a butterfly’s wings. This also confirms the 11-year sunspot cycle.
B stars – Stars of Spectral type B that are massive hot blue stars with surface temperatures of about 10 000 to 28 000 Kelvin for main sequence stars and up to 30 000 Kelvin for supergiants. Absorption lines of neutral helium (He I) dominate the spectrum, reaching maximum intensity in B2 stars. A few B stars also have emission lines from a circumstellar shell of gas. These stars can be found e.g. in the spiral arms of galaxies. Examples in our galaxy are: Spica, Rigel, Bellatrix and Alpha Crucis.
Wolf Lange