When is the best time to observe Rukbat?

Rukbat is best observed from June through August, with peak visibility during July when it transits around midnight in the Northern Hemisphere.

Where is Rukbat located in the sky?

Rukbat lies in the constellation Sagittarius at right ascension 19h 24m and declination -40° 37′.

What telescope do I need to see Rukbat?

At magnitude 4.0, Rukbat is visible to the naked eye from dark skies, easy in any binoculars.

Rukbat — Star in Sagittarius

HIP 95347; Alpha Sagittarii

Magnitude 4.0^m Star Sagittarius (Sgr) Visible

Star Map + List + Plan

About Rukbat

Description

Rukbat, Alpha Sagittarii, is a blue-white B8 V main-sequence star about 170 light-years away, notable for being the "Alpha" designation of Sagittarius despite being far from the brightest star in the constellation. It shines at magnitude 3.97, and the Sagittarius alpha status reflects Bayer's 17th-century labeling rather than modern brightness rankings. Rukbat has a weak infrared excess consistent with a circumstellar debris disk.

Observing Tips

Rukbat lies in the southern portion of Sagittarius, south of the Teapot asterism. It is a crisp blue-white naked-eye point. Finding Rukbat requires tracing Sagittarius far enough south to skirt the southernmost parts of the Milky Way. Best observed from mid-latitudes during June-September.

History

The name Rukbat comes from the Arabic "rukbat al-rāmī," meaning "the knee of the archer." The IAU adopted the name in 2016. The "Alpha" label dates from Bayer's 1603 Uranometria; Bayer assigned Greek letters partly by position in the figure, not purely by brightness.

Fun Facts

Rukbat's debris disk resembles our own Kuiper Belt scaled up — a young analog that may preserve clues about planetary formation timescales. Despite being the alpha star, Rukbat would be classed merely as one of Sagittarius's many modest B-type stars if modern catalogs had been first to label it.