BINARY SYSTEMS. 



547 



42 Coronas 

 Herculis 

 Struve 3,121 

 rj Coronas 

 Sirius 

 Cancri 



26 years. 

 35 years. 

 40 years. 

 40 years. 

 50 years. 

 58 years. 



| Ursae Majoris 

 TJ Coronas Borealis 

 a Centauri 

 H Ophiuchi . 

 X Ophiuchi . 

 Scorpii 



63 years. 

 67 years. 

 77 years. 

 92 years. 

 96 years. 

 98 years. 



Fig. 613. Monocerotis. 



It must be borne in mind that although these double stars appear close 

 together from our standpoint, they may be far apart 

 one behind the other in a straight line. When such 

 " pairs " exist they are known as optical pairs, or opti- 

 cally double stars, as distinguished from the actually 

 physical " pairs " which revolve round the centre of a 

 system. In Orion there has been discovered a regular 

 system, and the 6 in Orion, which appears in a com- 

 mon telescope a moderate star, and to the unaided 

 eye only a speck of light, is really composed of seven stars four are set in 

 the form of a trapezium, as figured in the diagram in the margin by dots and 

 asterisks. Two of these have been ascertained to possess 

 attendants indicated by dots, and a seventh star was 

 discovered by Lassell, and Humboldt remarks that in 

 all probability this apparently tiny star in the con- 

 stellation Orion constitutes a real system, for the five 

 smaller stars have the same proper motion as the 

 principal one. 



Fig. 6i 4 . Trapezium of Orion Thus our imagination almost fails to grasp the 



infinity of the systems with our single sun, and with 



the distant double and even triple suns round which planets revolve 

 perfectly independent of the other systems, as we are independent of them 

 possessing heat and light from their own sun or suns as we receive it 

 from ours, day and night seasons succeeding each other, and the wondrous 

 varieties of the light produced by the appearance or withdrawal of a sun 

 or two in the firmament of those most distant planets. These suns 

 being double or triple would affect each other ; the composition of the 

 light given forth would produce as we may assume varying effects. We 

 know something about the light of the stars by the spectroscope, and the 

 colours of stars are due to the vapour which takes away a certain part of the 

 light emitted, leaving the remainder to descend. through the atmosphere to us. 

 Binary stars are most numerous of the doubles ; for instance Castor, 

 rj Coronae, Rigel, Polaris, Mivac, y Leonis, y Virginis, Ursae Majoris, 

 a Hercules, 36 Andromedae, X. Ophiuchi, and TT Aquilae. The illustration in 

 the margin is Castor (or a Geniinorum), the most northerly of the Twins. 

 The 77 Coronae is also figured, as are Polaris (see fig. 6 1 o ante.), Bootes, Rigel, 

 and y Leonis. 



The cuts herewith illustrate the relative positions at the periods named 

 of the " doubles," and of the revolution of suns around other suns as 



