Page:Star Lore Of All Ages, 1911.pdf/248

176 In the neck of the Swan, not far from Beta Cygni, is the variable star χ Cygni, discovered by Kirch in 1686, ranging from magnitudes 4.5 to 13.5 in 406 days. Sometimes at its maximum it reaches only the sixth magnitude, thus presenting a problem which is one of the most interesting in all the realm of astrophysics.