Three of the long-period variables (LPV) on the sections observing program are now visible in binoculars. T UMa, S UMa and Chi Cygni (Mira) are now all visible in binoculars.
All three stars are typical LPV and show a variation of several magnitudes over the course of several hundred days. For most of their period they are two faint to be seen in anything other a large telescope. So, this is a good opportunity for binocular users to make some useful observations.
All LPV are cool, red giant stars in the later stages of their life. These stars can be thought of as consisting of two parts; a high density core surrounded by a low density outer layer. Shock waves emanating from deep within the star’s interior, coupled with the star’s low surface gravity, means that these stars can pulsate. It is these pulsations, these variations in the star’s radius, that cause the star’s variation in brightness.
In about five billion years from now, our own Sun will become a red giant star. It’s something to consider, that when observing these stars, you are looking at the Sun’s future.