59 Sagittarii is a single star in the southern constellation of Sagittarius, about a degree to the south of Omega Sagittarii near the constellation border with Capricornus. It has the Bayer designation b Sagittarii, or sometimes b¹ Sagittarii, while 59 Sagittarii is the Flamsteed designation. The star is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.544. It forms the southeast corner of the asterism called the Terebellum. Based upon parallax measurements, the star is located approximately 830 light years away from the Sun. It is moving closer to the Earth with a heliocentric radial velocity of −16 km/s.

This is an aging bright giant star with a stellar classification of K2.5IIb, having exhausted the supply of hydrogen at its core and expanded to 100 times the radius of the Sun. It is 64 million years old with 6.2 times the Sun's mass. The star is radiating 2,825 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,204 K.