Minor planet 29 Amphitrite reaches opposition on 22 February 2021 when it can be found shining among the stars of Leo, the Lion at mag. +9.1.

At 00:00 UT on 1 February it can be found south of mag. +6.9 TYC 852-1298-1, about a degree north-northeast of the mag. +9.5 elliptical galaxy M105 near the Lion’s belly.

At the start of February, Amphitrite will be at mag. +9.6: its dimmest for the month. The asteroid then brightens to mag. +9.1 by 20 February, remaining at this level until 24 February before dimming back to mag. +9.2 by the end of February.

For help understanding these values, read our guide to stellar magnitude.

Its track takes it into the body of Leo to end 4˚ northwest of Regulus (Alpha (α) Leonis) on 28 February.

An image of 29 Amphitrite captured by the Very Large Telescope. Credit: ESO
An image of 29 Amphitrite captured by the Very Large Telescope. Credit: ESO

Amphitrite is one of the largest S-type asteroids known, with a diameter around 200km. S-type asteroids are stony in composition (siliceous mineralogical). Approximately 17% of all known asteroids are S-type.

If its opposition is favourable, Amphitrite can reach mag. +8.6, but normally it hovers around mag. +9.5, the threshold brightness for average binoculars.

Amphitrite’s small magnitude range comes from its fairly circular orbit. A more eccentric orbit typically produces a more pronounced variation between brightest and dimmest magnitudes.

Its orbital distance from the Sun varies from 2.7 AU (410 million km) at aphelion to 2.37 AU (355 million km) at perihelion.

Amphitrite takes 4.09 years to complete each orbit, rotating once on its own axis every 5.4 hours.

The Moon will be in its fuller phases towards February’s start and end, but this shouldn’t stop you from seeing Amphitrite as the asteroid appears as a point source of light.

Have you managed to spot Amphitrite in the night sky this month? Let us know! Get in touch via contactus@skyatnightmagazine.com.


Pete Lawrence, astronomer and BBC The Sky at Night presenter.
Pete LawrenceAstronomer and presenter

Pete Lawrence is an experienced astronomer and astrophotographer, and a presenter on BBC's The Sky at Night.