Black silhouette in twilight sky, almond shaped UFO moving N to S at constant speed and low altitude

While walking out of K-mart I looked up at flock of birds in the twilight sky.  Above/beyond the birds I noticed an object slowly moving northward.  It immediately gave me chills because it didn't look like any flying vehicle I'd ever seen (and since I grew up in Wichita KS I've seem them all). 
For a moment I thought it might be a stealth fighter, since the nation was gearing up for the first Iraq war at the time, but the object had no wings or rotors or wheels, just a smooth oval (almond or maybe flattened egg) shape, slightly narrower in front, with a small oval bump on top. 
I couldn't determine surface details since the sun was down and I could only see a black silhouette against the sky.  It made no noise, there were no lights. 
When I first saw it, it was about 45 degrees up, to the west.  I estimate it was 20-30 feet wide, flying at approximately 1500' altitude moving north around 100mph (similar to a small private plane in size and speed). 
I thought 'hey, I see YOU' and looked around at other people in the parking lot, no one else was watching it. 
I observed it for a couple minutes until it disappeard over the horizon. 
After getting home I phoned the local airport and asked if they had any strange radar images or if anyone else had reported a UFO. They acted like I was crazy so I didn't bother to notify the police.
I considered the posibility that it might have been some type of balloon but it was moving much faster than the wind that night.
Observer info: Faculty member at the University of Illinois