225 Henrietta is a very large outer main-belt asteroid. It was discovered by Austrian astronomer Johann Palisa on April 19, 1882, in Vienna and named after Henrietta, wife of astronomer Pierre J. C. Janssen. The asteroid is orbiting at a distance of 3.39 AU from the Sun with a period of 2278.9 days and an eccentricity (ovalness) of 0.26. The orbital plane is inclined at an angle of 20.9° to the plane of the ecliptic. 225 Henrietta belongs to Cybele group of asteroids and is probably in a 4:7 orbital resonance with the planet Jupiter. This is classified as a C-type asteroid and is probably composed of primitive carbonaceous material. It has a very dark surface, with an albedo of 0.040. Photometric measurements made from the Oakley Southern Sky Observatory during 2012 gave a light curve with a period of 7.352 hours and a variation in brightness of 0.18 in magnitude. This is consistent with a synodic rotation period of 7.356 hours determined in 2000. In 2001, the asteroid was detected by radar from the Arecibo Observatory at a distance of 1.58 AU. The resulting data yielded an effective diameter of 128 km.