Un libro-stella per principianti; una guida facile alle stelle e agli usi astronomici del vetro-opera, del vetro-campo e del telescopio . o un osservatore con regali speciali di mente o di addestramento. Ma questo non è affatto il caso. Se le stelle cambiassero la loro posizione da notte a notte, la confusione sarebbe inevitabile. Ma, purchè la loro apparente rivoluzione una volta ogni 24 ore, i loro luoghi in relazione a ciascuna di esse sono stati praticamente inalterati per secoli non misurati. Mentre li guardiamo, impariamo velocemente mentalmente per raggruppare quelli più deboli circa il più luminoso, secondo i contorni o le figure

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A beginner's star-book; an easy guide to the stars and to the astronomical uses of the opera-glass, the field-glass and the telescope . o an observer withspecial gifts of mind or training. But this is by no means the case. If the stars greatlychanged their position from night to night, confusion would be inevitable. But, thoughmaking their apparent revolution once each 24 hours, their places in relation to each otherhave been practically unaltered for unmeasured centuries. As we watch them, we quicklylearn mentally to group the fainter ones about the brighter, according to outlines or figures * The two most important catalogues of the stars by magnitudes are that made by the Royal Observatory at Pots-dam, Germany, and that made by the Observatory of Harvard University, U. S. A. A list of the 70 brighteststars is printed on p. 140, showing their relative magnitudes. ^bc Stellar Moiib n that have descended to us from the past. Some of these traditional groupings seem tous illogical, but inasmuch as an attempt to change them (and to secure agreement as tothe change) would only increase confusion, they have been retained.. SPIRAL NEBULA, KNOWN AS MESSIER 51 From a photograph taken a! the Ierkes Observatory In one respect, however, a change has already come. The ancient world saw in thesegroups of stars the figures of birds or animals or mythological heroes. These fanciesserved, for many centuries, a useful purpose. It was possible to designate the locationof a star, for example, by reference to it as the brightest star in the head of the Dragon, or in the left foot of Andromeda, or in the head of Taurus, the Bull. But this method 12 H Beainncrs Star*:Book was necessarily crude, and never very accurate. In the seventeenth century (1603), aGerman astronomer named Bayer pubHshed a series of star-maps in which most of thebrighter stars in each group were designated by letters of the Greek alphabet.* Romanletters came also to be employed, as well as our ordinary Arabic figure

Parole chiave associate all'immagine

• bookcentury1900
• bookdecade19
• booksubjectastronomy
• bookyear1912