What are the characteristics of globular cluster M 15?

The globular cluster M 15(NGC7078) in Pegasus is an unusual globular cluster, and it is the only globular cluster known to contain planetary nebulae. Its position is: right ascension 21:30; Declination 12 10' (2000.0).

1957, a planetary nebula (K648) was discovered in the member celestial bodies of M 15. M 15 is the only globular cluster containing planetary nebulae, which is obtained by spectral analysis. It shows three emission lines from the gas shell of the planetary nebula. However, this planetary nebula does not seem to be a real member of the cluster, because it is too young compared with other ancient stars in the globular cluster. The spectral type of M 15 is F0 and the color index is -0.08. The average magnitude of the 25 brightest stars is 14.3 1, and the true diameter of the cluster is about 27 parsec or 88 light years. Shalip's early research results show that the distance of cluster M 15 is 13. 1000 parsec, the book of Czech astronomer Backvall gives 15. 10000 parsec, and the measurement result of T·D· Jin Man is/kloc. Generally, the value is 15. 1 thousand parsec, that is, 49,500 light years.

M 15 is a beautiful and bright globular cluster with a prominent bright core, and the surrounding stars are clearly identifiable in a large range. Angle diameter is not less than 8', brightness is 6.5, etc. When the weather is clear and there is no moon, you can see M 15 with the naked eye. As A smith pointed out, the outer contour of a cluster is not circular, so it is not difficult to see that its exterior is uneven.

M 15 is a very beautiful cluster, and the stars in it can be distinguished with a small telescope and with a medium-caliber telescope. The planetary nebula K648 contained in the cluster is very small (angular diameter is 3 "), and its magnitude is only 13.8, so it is difficult to determine its position. 1980, American astronomers Adams Payne and Heaton determined its coordinates as right ascension: 2 1: 27: 34, and declination: k1157'14 (1950 There is a pair of binary stars σ 2799 at the southwest of M 15 1, with an apparent magnitude of 7.4 and an angular distance of about 1".5.