The kite-shaped constellation Böotes, the Herdsman, is best known for its brilliant yellow-orange star Arcturus, the third-brightest individual star in the heavens. Böotes was one of Ptolemy’s original 48 constellations in the first century. The origin of the constellation is unclear, but one reference has Böotes moving a celestial plough (Ursa Major) around a pivot point marked by the north star.
While Böotes is a large constellation, it holds just a handful of deep-sky sights for small scopes. The region has the lovely globular M3, of course, just over the border in Canes Venatici. But unlike neighbouring Virgo and Coma Berenices, Böotes contains few galaxies. Indeed professional astronomers have recently mapped out what’s called the “Böotes Void”, a spherical region of space some 250 million light years across, which contains just a few dozen galaxies (see image above).
But Böotes does hold some fine double stars that make excellent targets for small telescopes. My favourite is the star Izar, or ε (epsilon) Bootis. Find Izar up the east side of the “kite” and north from Arcturus. The star is also called Pulcherrima, which is Latin for “most beautiful”. The star has components of magnitude 2.6 and 4.8, but they’re a close 2.9” apart. This requires at least 100-150x to split in a 4” scope. In nights of very unsteady seeing, the pair might be difficult to split in any telescope.
Izar’s primary is a yellow-orange giant, and the secondary is a white main sequence star. To some observers, the primary causes the secondary to appear not white but blue or even purple. This pair revolves around each other in 1,000 years and lies about 200 light years from Earth.
From the northern hemisphere you can see Böotes rising high in the eastern sky by 10 p.m. in April and 8 p.m. in May. And southern observers: you can see Arcturus, Izar, and the rest of Böotes well over the northern horizon this month and next.
Publisher’s Note: An earlier version of this article suggested the globular cluster M3 lies within the boundaries of Bootes. It lies in the constellation Canes Venatici.