Bootes

by Shaphan Shank | Jun 1, 2023 | 0 comments

M3 star cluster
M3. Photo © Reinhold Wittich/Dreamstime.com.

Bootes lies nearly straight overhead on June evenings in the Northern Hemisphere. This constellation is relatively easy to find, not only because of its distinctive kite-like shape, but also because it contains the fourth-brightest star in the night sky, Arcturus. Arcturus marks the point at the bottom of the “kite” of Bootes.

Although Bootes is a fair-sized constellation, it lies in a relatively empty part of the sky. The galaxy-rich spring constellations lie just to its west, and the summer Milky Way, with its clusters and nebulae, lies to the east. As a result, most of the telescopic targets in Bootes are double stars. Bootes holds quite a few of these stellar pairs, but for now we’ll just focus on two of its best doubles: Izar and Xi Bootis.

Izar is the second-brightest star in Bootes. It lies at the midpoint of the constellation’s “kite” shape, about 10° northeast of Arcturus. Izar is a tight double, with its component stars separated by only about 3 arcseconds. At low magnification, it looks like an ordinary bright yellow star. Higher magnifications (try a minimum of 150–200×) should reveal a bluish companion star right next to the golden primary component.

You’ll only be able to split tight double stars like Izar on nights with good seeing—that’s the astronomer’s term for a steady atmosphere. You can get a good idea of whether the atmosphere is steady or turbulent by looking at how much the brighter stars are twinkling. If they are barely twinkling, you’ve probably picked a good night for looking at tight doubles and other objects with fine details (the planets, for example). If the stars are twinkling significantly, a magnified view of Izar will only look like a fuzzy, flickering bead of light.

Another outstanding double, Xi Bootis, lies about 8.5° east of Arcturus and 8° south of Izar; it forms a nearly equilateral triangle with these two stars. Xi Boo is easier to split than Izar, but it is still moderately tight, with a separation of about 5 arcseconds. You should be able to split the pair with moderate magnification (100× should give a nice tight split), revealing a yellowish primary star alongside a more vivid orange secondary.

Although none of the deep sky objects in Bootes are very impressive with a mid-sized telescope, there is an outstanding globular cluster just across the official boundary in the neighboring constellation Canes Venatici. This cluster, M3, lies directly between Arcturus and Cor Caroli, the brightest star in Canes Venatici. M3 lies slightly closer to Arcturus, but it is within 1° of the midpoint between the two stars. M3 is bright enough to be easily visible as a fuzzy spot of light when viewed with binoculars, but you’ll need a telescope, preferably an 8” or larger, to really do justice to this cluster. At high magnification, a mid-sized telescope should be able to resolve stars across most or all of the cluster.

star map of Bootes

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