August 11, 2017 – Double Stars


Albireo in the constellation Cygnus (The Swan)

Evening Highlights:
  • Albireo: Appearing as a single star in the constellation Cygnus, through a telescope it resolves to a beautiful double system of gold and blue.
  • Alcor and Mizar: Found in the handle of the Big Dipper/Ursa Major, it’s one of the few naked eye double stars.  Even more interesting – it’s actually a sextuple system!
  • Epsilon Lyrae: Found in Lyra, if looking through binoculars you’ll see two widely separated stars.  Look through a telescope, and you’ll find that each ‘star’ is actually a double!
  • Saturn: With its rings tilted to over 27 degrees this year, it will be tonight’s focus for planetary viewing.  Jupiter and Mars will also be visible.

Why are double stars interesting? It’s estimated that in our galaxy alone over 50% of stars are actually multiple-star systems, which puts our sun in the minority.  Also, through studies of binary systems many properties of stars and star formation have been identified.  There are actually many different kinds of binary star systems, but the ones we’ll be seeing tonight are either optical doubles, which look like stars that orbit each other but simply just lie along the same line of sight, and visual binaries, which are stars that do truly orbit each other.  Alberio, for example, we don’t actually know if it’s a optical or visual binary.  If it is a visual binary, the orbital period (the time it takes for the stars to make one complete orbit of each other) is probably at least 100,000 years!

Presentation Links

Sky Safari:
Kepler Star Wheel (Planisphere):

Tonight’s Images

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