Comets and Asteroids
The path of asteroid Flora points the way to open clusters lurking near Gemini’s feet
Asteroid Flora.
Asteroid Flora is well positioned this month, passing through the southwest part of Gemini, in the direction of a group of open clusters that reside close to the mythological twin Castor’s foot. The asteroid
starts the month as a binocular target of mag. +8.2, but fades by one magnitude to +9.2 by the end of January.
Flora was the second asteroid discovered by John Hind. His first was Iris, which he identified on 13 August 1847. Flora was discovered two months later on 18 October 1847. It’s a large oblate body measuring 136x136x113km and is ranked as the seventh-brightest asteroid, with an average opposition magnitude of +8.7.
Flora reaches opposition on 2 January, half a magnitude brighter than this and close to its brightest achievable value of mag. +7.9. The asteroid reaches this peak brightness when opposition occurs close to Flora’s perihelion position. It spins once on its axis every 12.8 hours.
It’s a main belt asteroid, one of many orbiting between Mars and Jupiter and takes nearly four years to complete an orbit. Over this time its distance from the Sun varies between 1.86 AU and 2.55 AU. Flora is the closest of the large asteroids to the Sun and has the second closest mean orbital distance (2.20 AU) of the main belt asteroids, only beaten by 149 Medusa at 2.17 AU.
It is the lead member of the Flora family of asteroids, containing an estimated 80% of the group’s mass. This is a large family of silicaceous, S-type, or stony asteroids, thought to be the source of the body that collided with our planet and led to the extinction of the dinosaurs.
By 10 February, Flora will be 1° east-northeast of the mag. +5.7 open cluster Collinder 89, which itself sits 2° east-southeast of mag. +5.1 M35. Consequently, a wideangle sequence of images of this region from mid-January onward should reveal the movement of Flora towards the clusters. After 10 February, its track appears to bend north before continuing its journey northeast.