Asteroid 10 Hygiea reaches opposition in the constellation of Virgo, the Virgin
This month there are several low numbered asteroids reaching opposition, including 8 Flora on 12 April, 15 Eunomia on the 16th and 10 Hygiea on the 28th. Of the three, 10 Hygiea will be the brightest, reaching mag. +9.3 as it sneaks into Virgo, the Virgin having spent much of the month in neighbouring Libra, the Scales. On 1 April, 10 Hygiea can be seen 5˚ to the southwest of mag. +2.7 Zubenelgenubi (Alpha2 Librae). Zubenelgenubi is a double star, the mag. +2.7 primary having a mag. +5.2 companion, which is 3.8 arcminutes to the northwest of it.
As the month progresses, Hygiea performs a gently arcing movement to the west-northwest, crossing the border between Libra and Virgo on the night of 22/23 April. It begins its monthly path at mag. +9.9, brightening to its peak opposition brightness of mag. +9.3 on the 25th, a level it maintains to the month’s end.
10 Hygiea was discovered on 12 April 1849 by Italian astronomer Annibale de Gasparis at the Naples observatory. It’s a large body located in the main asteroid belt, with dimensions of 450km x 430km x 424km. It’s estimated to contain 3 per cent of the total mass of the main asteroid belt. 10 Hygiea takes 5.57 years to complete one orbit of the Sun at an average distance of 3.1 AU.
As a C-type or carbonaceous asteroid it was once considered for dwarf planet status, mainly by virtue of its nearly round shape, which is close to what you’d expect if it had undergone plastic deformation due to gravity, also known as hydrostatic equilibrium. It’s now believed that Hygiea’s shape is due to it being a ‘collisional family’ object, a body disrupted by an impact which resulted in fragments coming together to form it.