Welcome to OZNZ Extras

The smallest asteroid included in Steve Preston’s predictions¹ has a diameter around 15km. This is to limit the size of the world wide search and to include events where the probability of success is reasonably good. This is not a criticism; it’s just that the limit has to be set somewhere.

The fact is, the smaller the asteroid, the larger the asteroid’s positional errors, the lower the probability of seeing a positive event. But the probability is not zero.

The position of most stars in the sky are known to a few milli-arc-seconds (mas), thanks to the Hipparcos Satellite. A positive observation for any asteroidal event is highly valuable because now we can tie the position of the asteroid to that of the star at the instant of the event. All positive asteroid occultations for which there is absolutely no doubt involved are reduced to the Geocentre² and submitted to the Minor Planet Centre. Further, when the known position of that star is improved, then the position of the asteroid at event time is also improved.

Three or more positives events are required to obtain information about the asteroid’s profile and for small asteroids this is not impossible but unlikely. Why? Well due to the low probability of these events, observers are not encouraged to “chase the shadow” because there is simply no point driving to the centreline when the probability at the centreline is no better than anywhere in the 1-Sigma zone.

Due to the brief nature of even a central event, these events are ideal for time inserted video, where good signal to noise light curves can be made due to the mag. 10 or brighter star.

These events are set up to be distributed via Occult Watcher³. To receive these predictions, simply install Occult Watcher and subscribe.

Good luck.

Regards

DaveGault