Stars

Stars. Most of the celestial bodies keep the same apparent distance from each other and are known as the fixed stars; they differ from the planets by a peculiar twinkling of their light. [SCINTILLATION.] On a very clear starry night about 2,000 stars may sometimes be scen by the eye alone in the northern hemisphere, but countless numbers are brought into view by a powerful telescope. In early times the stars were divided into constellations, these being named after some animal or mythological person to which they bore some fancied resemblance. The positions of the stars in the constellation were then noted. Some stars were considered brilliant enough to merit a special name, such as Sirius, Algol, etc. Early in the seventeenth century Bayer produced a celestial atlas in which he named the different stars in each constellation after the letters of the Greek alphabet. Thus we have α Tauri (Aldebaran), α Canis Majoris (Sirius, or the Dog Star), β Orionis (Rigil), etc. The Greek letters are supposed to represent the order of brightness of the different stars in their constellation, α denoting the brightest. When the Greek letters are used up, ordinary letters are called in, and finally numbers are invoked. The description of the position of stars is, however, often given in a confusing manner from different catalogues, so that photographs of the sky are much more easily understood. Stars are divided into magnitudes according to their brightness with respect to all other stars regardless of any particular constellation, and those down to the 16th and 17th magnitude can be viewed with the best telescopes, the 6th being only just visible to the naked eye. The difference in brilliancy is due to the fact that the stars themselves are not equally bright, and also that their distances from us vary enormously. Some stars, however, have different magnitudes at different periods. These are known as variab1e stars, and the change in brightness occurs over regularly recurring periods. Double stars generally exhibit different oolours - fo instance, the two stars known as α Herculis are respectively red and blue. But single stars differ greatly in colour; Alrlebaran is red, while many stars exhibit a white or b1uish-white colour. The fixed stars experience changes in their number. Some disappear, while new stars sometimes start into existence. In 1572 it is recorded that a new star brighter than Venus appeared in Cassiopeia but its colour and brightness gradually underwent change until at last it vanished. It may be that these new stars are simply recurrences of variable stars of very long periods. By means of careful observations on the annual parallax (q.v.) of the stars the distances of some of them have been measured. α Centauri in the southern hemisphere gives the greatest value of this parallax (75 seconds), and is therefore the star nearest to us. In spite of this, however, It is so far away that light takes 4-1/2 years to travel the distance. Light from the pole star takes over 42 years. Most of the stars are, however, so far away that their parallax is too small to be observed. Besides nebulae (q.v.), clusters of stars very near to each other can be observed in different spots, and the individuals in these groups seem to exercise some influence upon each other, but their real connection is not undertood. It has been observed that some of the stars have a motion in the sky which is known as the proper motion of the stars; in some cases it amonnts to an apparent motion of 7 seconds a year, which means an immense real velocity of the star itself. The speotroscope [SPECTRUM] has revealed the constitution of many of the stars, and has shown that they are bodies very like the sun. It has hence been inferred that they are suns, and the sizes and brilliancy of some of them have been calculated; many are thousands of times gteater and more luminous than our sun.