Binary and Multiple Stars

Click here to view a binary star from Messier’s catalog

The icon shows the 4-star system M73.

Binary and multiple stars are common in the universe. Stellar formation

results in multiple systems at least as often as in single stars like our

Sun, as observations suggest.

Although Messier’s catalog was intended to contain only nebulous objects

which may be taken for comets, and which we today have found to be

clusters, nebulae, or galaxies, and not binary or multiple stars which

hardly fall in this category, two have found their way into the Messier

catalog: M40 and M73.

These entries both were more positional notations, in the case of M40

for a mistake of Hevelius who had reported a nonexistent nebula, and in

the case of M73 for an auxilary position to measure M72.