[Geritol]

Boy am I confused! Why are half the sky objects moving, half not moving? Is the angular velocity of the asteroid belt objects the same as the angular velocity of the planet's rotation? Or are they very bright objects that just blinked once? Or is this an overlay of a time lapse and a more sensitive still?

[LibWhacker]

Wow, nice catch, Geritol! I hadn't even noticed that! Photograpic anomalies? I have NO idea.

[LibWhacker]

However . . . I have seen photographs like that before. I'm trying to remember why astronomers make them . . . No luck yet . . . But I'm still looking for an explanation . . .

[ElkGroveDan]

Its a bit complicated, but the objects without trails are very dim stars. As the dim star moves across the sky a small point on the film in the center of the erstwhile startrail gets light the entire time allowing the exposure to build up until enough photons gather to be seen. The points at the beginning and end of the star trail just don't get enough light to show up. Does that make sense?

As for the other small movements in directions different from the star trails that others have mentioned here, I am guessing many of them could be small meteor trails. Mars certainly gets its share of meteors, but since the atmosphere is so thin they probably don't burn up us spectacularly as they do on earth. So I'm guessing those little grains of sand and dust make little winks rather than fiery trails we are accustomed to..

[green iguana]

"Boy am I confused! Why are half the sky objects moving, half not moving?"

The dots in the pictures are sensor noise. If you have a digital camera, try taking a very long (30 seconds plus if you can) photo with the lens blocked. The longer the exposure, the more noise is picked up, which is why the three photos get noisier (more and brighter dots) as the star trails get longer.