Updated: Sep 4
The stars and constellations that make up the Spring Triangle reach their highest point as the season comes to an end, making for a perfect time to observe the nearby "Realm of the Galaxies."
We're coming down to the home stretch of the spring season and this week, soon after nightfall, two constellations associated with the vernal season are reaching their highest point in the southern part of the sky: Boötes the Herdsman and Virgo the Young Maiden. Zero magnitude Arcturus and first magnitude Spica are, respectively, the brightest stars in these star patterns.
Now, were we to add the second-magnitude star Denebola, from nearby Leo the Lion, we can then trace out a large, nearly perfect equilateral triangle. George Lovi (1939-1993), who for many years penned the "Ramblings" column of Sky & Telescope magazine, called this pattern the "Spring Triangle," perhaps by analogy with the more famous Summer Triangle (made up of the stars Vega, Altair and Deneb).
However, in his book "A Primer for Star-Gazers," Henry Neely (1879-1963) described Arcturus, Spica and Denebola as the "Virgo Triangle." In either case, it's an easy pattern to identify in our current evening sky, both for stargazing novices and for navigators. Unlike the Summer Triangle, however, the Spring (or Virgo) Triangle is nowhere near the Milky Way.
Be that as it may, the Spring Triangle does overlap a vast number of other "milky ways." But more on that later.
The host constellations
Of the two constellations that supply the two brightest stars of the Spring Triangle, Virgo may not be easy for some beginners to trace out, but it does have Spica as a convenient starting point. Much fainter stars located above and to the west of Spica form a cursive Y-shaped pattern.
To American stargazers, Boötes is the Herdsman or the Bear Driver, an allusion to the way he follows the Big Bear (Ursa Major) around the sky. To the British, he is the Ploughman, since he follows the Plough (better known to us as the Big Dipper) around the sky. Boötes brightest star, the orange-yellow Arcturus, holds the distinction of being not only the brightest star in the Spring Triangle but the fourth brightest in the entire night sky.
Many pronounce the Herdsman's name incorrectly as Boo-teez, instead of the way it should be, Bo-oh-teez. Take note of the umlaut over the second 'o' (Boötes) to prevent this mispronunciation.
The best way to identify Arcturus and Spica is to first locate the Big Dipper, which is now located almost directly overhead during early evenings. Following along the curve of the Dipper's handle you'll be tracing a broad arc. Eventually, you'll come to Arcturus, quite unmistakable due to its brilliance and eye-catching fiery color. Now continue your imaginary arc past Arcturus and eventually, you will arrive at a bluish star shining with about one-third the radiance of Arcturus.