Double Stars: Course of the Eye Examiners
There are a number of double stars in the spring sky, some of which can be seen separately with a keen eye. Whether as a challenge for our eyes or for our understanding of stellar physics: It's always worth taking a closer look!
Binnies and multiple stars are very common in the sky. However, many can only be recognized as such in the telescope – if at all. This is because very close double stars cannot be seen separately, even in large telescopes. Only when their light is broken down into its individual colors with the help of a spectroscope does their true nature reveal itself on the basis of the spectral lines. These are spectroscopic binary stars. Only when the orbits of the stars are further than the orbit of Neptune around the sun and when the star system is less than a hundred light-years away from us, there are angular distances in the range of a few arc seconds in the sky, so that the stars of the system can be seen with an amateur telescope are individually visible.
In many cases, there are clear differences in color and brightness (see image on p. 70 below). Such contrasts, which are attractive to the eye, are also of particular interest to astrophysicists, namely as a test of their star models: after all, two stars formed here together. Thus, despite their often different masses and stages of development, they are exactly the same age, initially had the same chemical composition - and as a true double star they still form a bound system today. The brighter and more massive partner may then have already developed into a red giant, while a less massive companion, which is more economical with its fuel supply, develops more slowly and therefore still shines as a normal star in pure white …
