Page:In starland with a three-inch telescope; a conveniently arranged guide for the use of the amateur astronomer, with forty diagrams of the constellations and eight of the moon (IA instarlandwithth00olcorich).pdf/17



at the north point, and proceeding through the east, The student should bear south, and west to the north.

mind in this connection that in the telescope the north and south points are reversed. The decimals are omitted from the distances given between the doubles (which are from centre to centre, and in seconds of arc) as in the wider doubles, as most of those referred to in the text would be termed, absolute in

accuracy in measurements, for purposes of observation purely, is non-essential. A three-inch glass should split stars that are distant from each other 2.3". Of course this question of splitting

doubles depends in a great measure on the power of the eyepiece used, the condition of the atmosphere, and the Serviss recomquality, of the eyesight of the observer. mends a power of from fifty to seventy to the inch of aperture.

The author has succeeded

majority of the doubles power of 130.

mentioned

in seeing the great in the text

with a

The term "light year" which is used in the text is the usual term for expressing the distance from the earth to the stars. A light year is the unit of such measurements, and

is simply the distance light travels in a year, the speed of light being 1 86 ceo miles per second. Expressed in figures it gives 5,785,344,000,000 as the distance in miles that light travels in one year. When it is added that (61) Cygni, the nearest star to the earth the northern hemisphere, is nearly six light years ,

m