Star
2 of the 7 encyclopedias on this shelf carry an entry for Star. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
one of the self-luminous bodies which surrounds our solar system on all sides. They are distinguished from the planets by their flickering light, by the comparative constancy of their relative positions in space, and by their inappreciable diameter even when viewed by the most powerful optical instruments. The number of stars visible to the naked eye is estimated at about 5,000; and these in constellations and classified according have early been grouped to their brightness or magnitude. Those belonging to the first six magnitudes are visible to the naked eye; but the telescope reveals myriads which are distinguished down to the 16th magnitude. The earliest catalogue which has come down to us is that in Ptolemy's "Almagest," supposed to have been compiled by Hipparchus (150 b. c.). Ptolemy gives 1,030 stars, of which several cannot now be certainly identified. The last important catalogue before the invention of the Brahe, who its life history telescope was that of Tycho greater accuracy not be really redetermined with still Of modern much Argelander's " Sternverzeichniss" is the largest, enumerating more down to the 9th magnitude, than 300,000 pole and 2° S. all situated between the Apthorp Gould of the equator. Benjamin , , extended this an American astronomer Southern Hemisphere catalogue to the Cordoba, South at the Observatory of America. The large majority of stars are of conare certain, stant magnitude, but there stars, which vary in known as variable periodically. Algol, brightness and vary Perseus, fluctuates in the constellation 4th magnitudes in between the 2d and days. Mira in a period of about three is such another the constellation Cetus to the naked star, being ing usually invisible bursting out at intervals of 11 eye, but brilliancy of a second months with the star. There are or third magnitude many others. At times, stars have sudnone were known denly appeared where remarkable of these before. The most Brahe are the one described by Tycho by Kepler (1604- (1572), that observed star of 1866 which blazed 1606), and the Borealis. Near out suddenly in Corona small telescopic the place of the first a the last was entered star now exists, and in Argelandas a 9th-magnitude star spectrum of the 1866 er's catalogue. The Huggins consisted star as examined by crossed not of a continuous spectrum absorption lines only by the usual dark , bright lines which corbut also by the spectrum lines responded in part with general similarity of of hydrogen. The the solar spectrum the stellar spectra to , if any further is a convincing vincing proof our sun is a star, and were needed, that suns with a probable that the stars are planets. retinue of accompanying According to the nature of their grouped under spectra, stars have been , of which Sirius, the four types, Type I. a good represenbrightest known star, is by a continuous tative, is characterized very few absorption spectrum with a type II. the spectrum lines crossing it; in fine lines, as in is crossed by numerous III., to which the sun's spectrum; in type Herculis belong, fluted a Orionis and a in type IV., spaces begin to appear; and the red stars, fluted which includes Here there is an evispaces only exist. the spectrum of few dent gradation from by gaps. absorption lines to that broken to the accepted theory of spec- According spectrum inditrum analysis, the former temperature than the cates a higher is an evidence of a delatter, so that here individual star. velopment in time of each As a star is cooling, its spectrum passes through all these types, and thus our sun is at a later stage in than Sirius, tho though it may the positions of 1,005 stars. any older, since it is probably catalogues, smaller than Sirius, whose development be slov slower. Our sun canwill therefore not be compared in size or splendor to , not a few some of its distant compeers peculiarly comof which must present Thus the telescope replicated systems. really doul veals many stars to be double. One of the most interesting of these is of whose Sirius, from the irregularity Auwers had conmovements Peters and accompanied by an cluded that it was a large planet; attendant star or at least companion was disand in 1862 such a Clark in the very covered by the younger had predicted direction in which theory Its great minuteit to be at that time. hopeless except in ness renders detection circumstances. The movery favorable indicate similar tions of Procyon a doubleness, but its companion has not yet multiple stars been seen. Triple and are also not unforming one system Herculis, recommon. For instance, u a double star by Herschel, is cognized as the small Herschelreally a triple star, having been resolved into ian companion Clark. An intertwo in 1856 by Alvan ' of these binary esting optical property color of the one comsystems is that the the complement of ponent is frequently A very remarkable that of the other. , famous as the double star is 61 Cygni from the sun first star whose distance from its parallax, was calculated directly angular distance between i. e., from the from opposite exits positions as viewed orbit. The most tremities of the earth's various results probable mean of the for this paralgives about .5 of a second lax. This, however, is not the nearest star; away as a Cenit is nearly twice as far Henderson has tauri, which according to corresponding to a a parallax of 0".91, times the radius of distance of 226,000 than twenty the earth's orbit, or more miles (20 × 10¹²). millions of millions of light, which travels at In other words, miles per second, the rate of 236,000 years to pass from takes nearly three to us. The paralthe nearest fixed star the stars of the first lax of at least half than one-tenth magnitude is probably less that their average disof a second, so million radii of tance is greater than two Though, to the naked the earth's orbit. occupied the eye, stars have probably positions from the earliest same relative telescope reveals of historic times, the strictly fixed. Many that they are not motions, among have ap appreciable proper was before noticed. others 61 Cygni, as Its annual motion is 5".2, which is exceeded, however, by that of Groombridge, 1830, a star of the 7th magnitude, whose proper motion is 7". As a general rule, the brightest stars have the greatest proper motion, and stars below the 3d magnitude move only a few seconds n 100 years. This motion in the heavens cannot be taken even as an approximate estimate of the velocity with which any star is moving, since only the portion of the real velocity which is resolved perpendicular to the line of sight is measurable. Spectrum analysis has, however, given us a means of measuring the velocity along the line of sight. The physical meaning of the dark absorption lines which cross the spectra of the sun and stars has been pointed out under SPECTRUM ANALYSIS. They indicate the absence of certain rays of definite refrangibility and wave length from the solar or stellar light which reaches us. Since each star spectrum has its own peculiar lines, these must be due to absorption by by the star's own outer envelope or atmosphere. Now, exactly as ocean waves will appear shorter or longer than they really are according as the observer is sailing against or with them, so will the wave length of each individual ray be shortened or lengthened according as we approach or recede from the source of light, and each absorption line in the spectrum, corresponding as it does to a ray of definite wave length, will be displaced toward the violet or red respectively. By comparison with the spectrum of the substance to which a determined portion of these lines corresponds, this displacement may be measured, and from its relation to the particular wave length the ratio of the relative velocity of approach or recession of the star to the velocity of light can be easily calculated. Stars which show periodic variations of magnitude are called variable stars. Among these are Mira and Algal. Up to 1920 about 750 of these stars were known. Their average period of variation is about 300 days and some are 1,000 times brighter at maximum than at minimum. It is believed that these are the giants among the stars. At their maximum some are 150 times brighter than the sun.
Aiton's Encyclopedia (1910)
a heavenly body shining with its own light. This definition excludes the planets and their satellites, but includes the sun, which is supposed to differ from other stars mainly in our being near it. It is worth while to know that the stars twinkle but the planets do not. Many of the stars are larger and much hotter than the sun; some are smaller and cooler. Six or seven thousand stars are visible to the average eye. About 2,500 are visible at any one time. No one can see all the stars without observing in both hemispheres. About 100,000 stars may be seen with a common opera glass . Three times that number are visible through a small telescope. A telescope forty inches in diameter reveals possibly 100,000,000 stars. Stars not visible to the eye through the most powerful telescope may be photographed by the delicate instruments now in use by astronomers. It is impossible to say whether the stars thus noted are practically all there are in the universe, or whether we have only made a beginning in seeing them. The entire space of the heavens is charted in sixty-seven areas called constellations. This custom has descended to modern astronomers from the ancients, who were wont to decorate their charts with the figures of various animals and goddesses whose names were given to the constellations. The groups are thoroughly artificial, but are very useful in locating a star. Some of the brightest stars have individual names, but the great majority are designated by the name of the constellation and a Greek letter. Even this system fails in the case of telescopic stars, because the number of letters is not sufficient to name all the stars within one constellation. Astronomers have therefore resorted to numbers, each star being given its own catalogue number. The largest number in any one catalogue thus published is about one-third of a million. Of late charts have been formed by telescopic photography; that is to say, by a combination of the telescope and photographic camera. Harvard observatory employs fifty assistants and has accumulated many thousand photographs taken at Cambridge for the northern hemisphere and in Peru for the southern. An ingenious mechanical arrangement enables an observer to put his camera under control of clockwork so that the camera follows a particular spot in the heavens at exactly the same speed with which the earth would turn it away from that spot. If a luminous body in the area under observation moves, it creates a trail or path on the photographic lens, calling attention to its movement instantly. A series of such photographs furnishes a complete history of the movements of heavenly bodies. Stars are classified according to their brightness. The ancients recognized six magnitudes. The first magnitude includes about twenty of the brightest. It is estimated that all together the stars give about one-sixtieth as much light on a clear night as a full moon . Some heat is doubtless received from them, but the amount is so slight that it has been impossible thus far to detect it. As distinguished from the planets, the true stars are sometimes called fixed stars , but it is certain that many and perhaps all are in motion like our sun. See Arcturus ; Orion ; Pleiades ; Milky Way ; Telescope ; Observatory