COMETS AND ASTEROIDS

Observe minor planet 11 Parthenope reaching opposition in Pisces

Minor planet 11 Parthenope is a large body that orbits within the main asteroid belt between Mars and Jupiter. This year Parthenope has an opposition on 23 October when it will reach mag. +9.4 in Pisces. It starts the month off in Cetus, the Whale, immediately to the west of the small misshapen pentagon that represents its head. Then, during October it slowly tracks to the southwest, ending up just inside the pointed part of the portion of Pisces which is supposed to represent the rope tying two fish together.

The rope is in two parts and is ‘knotted’ at the star Alrescha (Alpha (a) Piscium). Parthenope’s brightness varies over the month, but only slightly. On the 1st it shines at mag. +9.8, and brightens to reach a peak of mag. +9.4. By the end of the month it will have barely changed, being at mag. +9.5. This makes it an ideal target for a small scope to track. Parthenope has a diameter of 153km and during favourable oppositions can reach a peak of mag. +8.7.

This area of sky is busy at the moment; Mars is nearby, reaching opposition on the 13th, while mag. +5.7 Uranus is near too, reaching opposition on the 31st. In terms of asteroids, eighth magnitude 8 Flora, 12th magnitude 45 Eugenia and 34 Circe, together with 11th magnitude 67 Asia, will all be in the vicinity.

Parthenope is an S-type, or siliceous asteroid, a type which accounts for around 17 per cent of all known asteroids. They tend to be bright with albedos (reflectivity) around 20 per cent.

Parthenope’s albedo is 18 per cent and its 3.84–year orbit takes it out as far as 2.7 AU from the Sun and in as close as 2.2 AU. It spins on its axis once every 13.7 hours. It was discovered by Annibale de Gasparis on 11 May 1850 and is named after a Greek siren who is said to have founded the city of Naples. Its name was originally suggested by John Herschel after his discovery of 10 Hygiea in 1849.