SPHERICAL ASTRONOMY. 89 
The Fixed Stars; their Size, Number, Arrangement, and Distances. 
11. By fixed stars is to be understood all those stars which are neither 
planets, nor moons, nor comets, deriving the name from the fact of never 
changing their relative positions when viewed with the naked eye. The 
fixed stars are the most numerous objects in the heavens, and are divided 
into eight classes, according to their various apparent sizes and brilliancy. 
We speak, for instance, of stars of Ist, 2d, 3d, 4th, 5th, 6th, 7th magni- 
tude, so that those of the 1st magnitude possess the greatest brilliancy, and 
those of the 7th are only visible to the very acute naked eye. To the 8th 
class, that is, to those of the 8th, 9th, 10th, &c., magnitudes, belong all 
those millions of stars which are only visible through the telescope, hence 
called telescopic stars. The color also, especially in the double stars, is 
very various. 
Although the fixed stars do not change their relative positions to each 
other, yet they have a common apparent motion, produced by the actual 
daily rotation of the earth on its axis; in addition to this, the annual revolu- 
tion of the earth about the sun produces various differences in their position 
with respect to the sun. Finally, there are other although very minute 
variations in the position of the stars with respect to the horizon, the equa- 
tor, the ecliptics, &c., produced by refraction, parallax, precession of the 
equinoxes, nutation, &c., which will be referred to hereafter, 
As the number of the stars is apparently infinite, it must necessarily be 
impossible for us ever to estimate it. Nevertheless, many astronomers 
have attempted to determine this approximately, at least with respect to the 
visible stars. The number of those of the first magnitude is 14, of the 
second, 70, of the third, nearly 300; that of stars of the 4th and succeeding 
magnitudes is much greater. The fixed stars stand so close together in 
many parts of the heavens, that any enumeration of these would be abso- 
lutely impossible. We need only examine the milky way through a good 
telescope, to discover that it consists of an innumerable number of fixed 
stars. Herschel at one time saw more than 59,000 stars cross the fixed 
field of his great reflector in a space of 30 degrees, near the club of Orion : 
at another time, he observed 258,000 to pass his 20 foot reflector in 41 
minutes. 
Lambert, in his “ Kosmologische Briefe,’ was the first to treat of the 
distribution and arrangement of stars in the heavens. It is in more recent 
times, however, since the discovery by Madler of the central sun of our 
system of fixed stars, that the first tolerably satisfactory explanation of the 
arrangement of the stars has been given. With respect also to the distances 
of the stars, nothing more definite was known than that the nearest of them 
was so remote as to require six years for its light to reach our earth. 
Bessel and Struve, however, by means of observations of the particular mo- 
tions exhibited by the double stars 61 Cygni, and Vega («) Lyre, have 
determined these distances with approximate accuracy. According to 
Bessel’s investigations, the distance between our sun and star 61 Cygni would 
be traversed by light within ten years. 
89 
