What is there to look at with a small telescope when the light from the Full Moon floods the sky? Galaxies and nebulae are swamped by the moon's natural "light pollution." Starlight still shines through, and gives astronomers some different targets to observe.
Nearly half of the stars in the sky are double or multiple. Many of these show startling contrasts in color and brightness, and are showpieces in even the smallest of telescopes.
If you look closely at Mizar, the star in the middle of the Big Dipper's handle, you may detect that it has a tiny companion. This star, Alcor, was known to the ancients, and was sometimes used as a test for good vision. In any binoculars, Alcor can be plainly seen as a separate star.
Not surprisingly, this was one of the first objects the earliest telescopes were turned on. In 1617 Benedetto Castelli wrote to his friend Galileo telling him that Mizar itself was also a double star, and asking Galileo to observe it and confirm this. This was the first binary star to be discovered. In 1889, Edward Charles Pickering turned his spectroscope on Mizar A, and discovered that it was also a close binary, the first spectroscopic binary discovered. There are few stars in the sky that have as many "firsts" as Mizar does!
The two stars which make up Mizar itself are almost equal in brightness (2.3 and 3.8 magnitude) and colour. The other double star we're going to look at, Albireo, is a contrast in both brightness and colour.
The brighter of Albireo's two components is a 3rd magnitude yellow giant. Its companion is very different: two magnitudes fainter and deep blue in color. This contrast of brightness and color makes Albireo one of the prettiest sights possible in a small telescope.
This article was provided to SPACE.com by Starry Night Education, the leader in space science curriculum solutions.
