May 27 – June 9, 2019
Mount Washington —Â While writing my recent column about bright stars in the south at nightfall, I was reminded of patterns those stars shape in addition to the position each has in an official constellation. Arcturus is the brightest star in the constellation Bootes the Herdsman; Spica brightest in Virgo the Virgin; and Denebola marks the tail of Leo the Lion. Draw imaginary lines to connect Arcturus to Spica and Denebola and we have the Spring Triangle, an asterism. Asterisms are easily distinguishable patterns often composed of stars from more than one constellation. In the case of the Big Dipper, the asterism is an outstanding part of one official constellation, Ursa major, the Great Bear.
A larger rendition of the Spring Triangle connects Arcturus, Spica and Regulus, the Lion’s alpha star. This version does not lend itself to visualizing the Great Diamond asterism – an extension of the Spring Triangle – whereas Denebola is in the perfect position to lead up to the dimmer star at the top of the diamond, Cor Caroli, 2.84m. Cor Caroli, Charles’ Heart*, is one of only two naked-eye stars in the constellation Canus Venatici, the Hunting Dogs. Look above and between Arcturus and Denebola to alight upon Cor Caroli. Look below to Spica to complete the Great Diamond, also known as the Virgin’s Diamond. Study the illustration that shows the diamond shape overlaid on each of the four constellations that contribute to it. Virgo the Virgin is at its base. Remember the diamond that Corvus the Crow is poised to snatch? Notice Corvus at the bottom edge of the diagram.
While venturing out at nightfall to enjoy the asterisms, be sure to appreciate the Crow careening in the south and the full figure of the Lion striding high in the southwest.
Stargazer’s calendar: Least moonlight makes for best two-week period for stargazing: last quarter moon yesterday, the 26th; waning crescent today rises in the east-southeast at 2:16 a.m., introducing a week of early-morning crescents in the east, also visible in the daytime sky. New moon next Monday, June 3, introduces week of evening crescents in the west. First quarter moon near Denebola on the 9th.
Resources
https://earthsky.org/favorite-star-patterns/spring-triangle-regulus-arcturus-spica
https://www.space.com/2418-star-sight-celestial-diamond.html
https://en.wikipedia.org/wiki/Great_Diamond
*https://en.wikipedia.org/wiki/Cor_Caroli
