342 HOW TO OBSERVE THE HEAVENS. 



The star y 1, (second magnitude), is on the wing of Pegasus, and is on the 

 meridian at the same time with the bright star a3 (first magnitude), which is 

 on the head of Andromeda. These two stars are on the meridian at midnight 

 on the 20th September. The star a 3 passes the meridian at New York about 

 12 south of the zenith. This is a double star. 



The four conspicuous stars a 3, y 1, a 1, and /? l, are easily recognised on the 

 firmament, the lines which join them forming nearly a square. The star # 3 

 (second magnitude), is a double star on the girdle of Andromeda, and lying 

 very nearly in the direction of the diagonal of the quadrilateral formed by the 

 stars a 3, y 1, a 1, and /? 1. The star 3, of the third magnitude, is on the breast 

 of Andromeda. 



The two stars <* 5, and /?5, which form the base of an isosceles-triangle, hav- 

 ing its vertex at the star /33, are in the head of ARIES, and are stars of the 

 third magnitude. The star & 5, is double. These stars are on the meridian 

 at midnight on the 20th October. 



The a 6 is a conspicuous star of the second magnitude called MENKAR, in 

 the constellation of the Whale (Cetus), and y 6, near it, is a double star of the 

 third magnitude, in the same constellation. 



The amateur observer may, from the examples which have here been given, 

 easily extend his acquaintance with the fixed stars. In the maps of the stars 

 published by the Society for the Diffusion of Useful Knowledge, already referred 

 to, he will find marked the days on which each star is seen on the meridian 

 at midnight. Its place on the meridian may be found by the following simple 

 rule, in which it is assumed that the place of the observer has north latitude : 



" Observe on the map the distance of the star from the celestial equator. 

 If the star be north of the equator, the difference between this distance and 

 the latitude of the place will give the distance of the star when on the meri- 

 dian from the zenith. It will be south of the zenith if the latitude of the place 

 be greater than the distance of the star from the equator north if less. If 

 the latitude of the place be equal to the distance of the star from the equator, 

 the star will pass through the zenith. If the star be south of the celestial > 

 equator, add its distance from the equator to the latitude of the place, and the > 

 result will be the distance south of the zenith at which the star will pass the j 

 meridian." The following examples will illustrate this rule: 



Example 1. It is required to determine the point at which the star Castor j 

 crosses the meridian of New York. ) 



By reference to the maps or a celestial globe, it will appear that the star J 

 Castor is 57 45' north of the celestial equator. The latitude of New York / 

 being assumed to be 40 43' N., we shall 

 From - 57.45' 

 Subtract - 40.43 / 



17. 2' 



and the remainder, 17. 2', will be the distance north of the zenith at which 

 Castor passes the meridian. 



Example 2. To find the point at which Fomalhaut passes the meridian of 

 New York. 



The distance of Fomalhaut south of the celestial equator being taken from 

 the map to be 30. 30', we shall 



To - 30-30 / 

 Add - 40. 43' 



71. 13' 



and the sum 71. 13' will be the distance south of the zenith at whijch Fomal- 

 haut passes the meridian. 



