Introduction of crow nest

Raven is one of the southern constellations. Located in the southwest of Virgo, between Dajue and Ophiuchus, it is an oblique quadrilateral composed of four third-class stars. In the quadrangle of Ursa Major, there are two stars, Ursa Major I and Ursa Major III, pointing to the southwest of Ursa Major. Ptolemy, an ancient Greek astronomer in the 2nd century A.D., listed this small constellation in his grand synthesis theory. There are few bright stars in corvus corax, and the image of crows is not obvious. The four brightest 3m stars in the constellation form an irregular quadrilateral, in which both γ and δ stars point to Virgo. The curve extending from the handle of the Big Dipper Ursa major passes through the big horn and the horn, and finally ends in this small quadrangle. This arc is called "big spring curve".