Asteroid 20 Massalia is a good target with a small telescope through the month

Asteroid 20 Massalia reaches opposition this month in Cancer, the Crab. It’s located near to the border of Cancer and Leo, the Lion on the 1st, 5˚ east-northeast of mag. +4.3 Acubens (Alpha (α) Cancri). It then tracks west-northwest along a line that takes it to a point about 4˚ southeast of mag. +3.9 Delta (δ) Cancri.

Massalia has an orbit that keeps it within the inner part of the main asteroid belt. It’s the parent body of a large group of asteroids known as the Massalia family, a collection which has over 6,000 members. Massalia is an S-type, or stony asteroid, with a mean diameter of 145km. Its orbital period is 3 years 9 months and its mean distance from the Sun is 2.41 AU (361 million kilometres). When at aphelion, its orbit takes it out as far as 2.75 AU from the Sun, and when at perihelion it moves in as close as 2.07 AU. Massalia is believed to be nearly spherical in shape, having triaxial ellipsoidal dimensions of 160x145x132km. It is also believed to have large, flat regions on its surface. Its rotation period is 8.1 hours.

Massalia’s geometric albedo is 21%, a figure that indicates how much incoming sunlight is reflected back from the asteroid’s surface. This leads to an apparent magnitude that ranges from +8.3 at favourable oppositions to mag. +12.0 at its least favourable oppositions. This month is favourable, Massalia reaching opposition on the 5th when it appears to shine at mag. +8.5.

On 1 February, Massalia is mag. +8.7, brightening by one-fifth of a magnitude as it reaches opposition. By the month’s end it will have dimmed to mag. +9.3.