From: "milton_aupperle" <milton@outcastsoft.com>

Date: October 26, 2011 2:22:24 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Asteroid Lucretia

Hi Folks;

I managed to record the light curve for Lucretia (Mag 13.7, 12 kilometers in diameter, Stoney type) last night:

http://www.outcastsoft.com/AstroImages/Lucretia_20111025_MJA.png

over a 4.6 hours, which is over 1 full rotational period (4.3 hour). Lucretia is nearly at opposition to the earth, so it's only ~0.92 AU away. That's 335 images taken at 50 second intervals and a focal length of 1625 mm.

I measured a rotational period of 4.361 +/- 0.027 hours and a change in magnitude of 0.34.

Assuming a constant albedo, the magnitude change means the asteroid is egg shaped with a 1.37 times long to short difference along it's rotational axis. Compare that to asteroid Budrosa:

http://www.outcastsoft.com/AstroImages/Budrosa_20111018_MJA.png

which has a 0.04 magnitude dip and likely has a rounder shape at 1.04 long to short axis ratio.

Lucretia probably has craters and ridges that are causing local brightness anomalies on the shallower sun lit side after maximum brightness and up to half way through the next rotation. That could mean the planar surfaces (i.e. crater walls, ridges) are reflecting sunlight back at us and have faces that are > 45° to the observer.

TTYL..

Milton Aupperle