Comets and asteroids

View asteroid 230 Athamantis reaching opposition as it passes into Libra

Asteroid 230 Athamantis reaches opposition on 22 May, when it will appear as a mag. +10.2 object passing into eastern Libra. It’s conveniently located during May, tracking from a position 1˚ northwest of globular cluster M80. This is one of two Messier catalogued globulars in Scorpius located close to Antares (Alpha (a) Scorpii). The other is M4, a globular that’s larger and brighter in appearance than M80. M80 appears 10 arcminutes across and shines at mag. +7.3, while M4 appears an impressive 36 arcminutes across and shines with an integrated magnitude of +5.4.

In its position north of M80 on 1 May, Athamantis is mag. +10.9. This puts it beyond average binocular range but well within the ability of a small scope. During May, the asteroid tracks northwest, passing between the stars representing the northern claws of Scorpius; Graffias (Beta (b) Scorpii) and Delta (d) Scorpii. It ends May less than 2˚ northeast of mag. +4.8 Kappa (k) Librae.

Number 230 in the ever-expanding list of recorded minor planets, now numbering over a million, Athamantis was discovered on 3 September 1882 by astronomer Leo Anton

Karle de Ball at the German observatory in Bothkamp, the only asteroid he discovered. It is an S-type, or siliceous asteroid, meaning it has a stony or mineralogical composition.

Athamantis has a diameter of around 111km ,which means that it’s larger than 99 per cent of known asteroids. It orbits the Sun once every 3.68 years in an orbit that takes it out as far as 2.53 AU and in to 2.24 AU. It’s placed between the orbits of Mars and Jupiter, making it a main belt asteroid. Analysis of the asteroid’s light curve has revealed that it rotates once on its axis every 24 hours; and over this period it varies in brightness by 0.2 magnitudes.