September: Prime Time for Asteroid Hunting

Although the number of asteroids we have is now up in the hundreds of thousands, many of those have been discovered by automated searches, within the past several decades; however, before the 1970s, finding a new little object was more a matter of search and search and search… To try their best, hopeful observers always looked most prominently around the ecliptic in the middle of the night, as away from the Sun as they could get.  The best time to do so was in September, near Pisces and other nearby constellations which are relatively “star-poor,” making it the best time to discover a new object.  Also, Jupiter, our largest planet and the one on the outer boundary of our major asteroid belt, has its perihelion there.  This allows it to align some of their orbits with its own, giving many of them their own perihelia in this similar region.  Because of this, of the first 1,940 asteroids discovered, 344 were found during September, more than twice the average of any other month.

Not surprisingly, the two worst months were June, with 65, and December with only 75.  There seem to be two good reasons for this discrepancy: First, both months are when the Milky Way is most prominent around midnight; and second, the differences in observing time.  June nights are very short, and December nights are too cold to stay outside for very long periods of time just to look for something that may or may not be there.  

At present, we are losing the two major asteroids (or asteroid and dwarf planet), Ceres and Vesta, that we’ve had for the last several months, so, before we lose them totally, take a last look before they leave our sky, and, maybe, just maybe, you might be fortunate enough to find an undiscovered minor body.  Happy observing.