1677 Tycho Brahe, provisional designation 1940 RO, is a stony Marian asteroid from the central region of the asteroid belt, approximately 12 kilometers (7.5 miles) in diameter. It was discovered on 6 September 1940, by Finnish astronomer Yrjö Väisälä at Turku Observatory in Southwest Finland.^[1] The common stony S-type asteroid has a short rotation period of 3.89 hours.^[5] It was later named after Tycho Brahe, one of the fathers of astronomy.^[2]

When applying the hierarchical clustering method to its proper orbital elements, Tycho Brahe is a member of the Maria family (506),^[4] a large family of stony asteroids.^[11]: 23 Based on osculating Keplerian orbital elements, the asteroid has also been classified as a member of the Eunomia family (502), the largest family in the intermediate main belt with more than 5,000 members.^[5]

It orbits the Sun in the central main-belt at a distance of 2.3–2.8 AU once every 4.03 years (1,472 days; semi-major axis of 2.53 AU). Its orbit has an eccentricity of 0.11 and an inclination of 15° with respect to the ecliptic.^[3] The asteroid was first observed as A916 UA at Bergedorf Observatory in October 1916, extending the body's observation arc by 24 years prior to its official discovery observation at Turku.^[1]

The asteroid has been characterized as a stony S-type by Pan-STARRS survey, and in the SDSS-MFB (Masi Foglia Binzel) taxonomy,^{[5][10][lower-alpha 1]} which agree with the overall spectral type for members of the Maria family.^[11]: 23

This minor planet is named for the great Danish-born astronomer Tycho Brahe (1546–1601) an early forerunner and father of modern astronomy. He is known for his unprecedented precise measurements in the pre-telescopic era.^[2] The official naming citation was published by the Minor Planet Center on 15 October 1977 (M.P.C. 4236).^[12] Brahe is also honored by the prominent crater Tycho in the southern highlands of the Moon and by the Martian crater Tycho Brahe.^[2] The bright supernova, SN 1572, is also known as Tycho's Nova.