p.2 #3 · I shot a 50 minute star trail (15 3-min exp.) but what are these...
Come on, guys---all this theorizing about simple astronomic facts!
The answer to the original question---the cause of the hot spots---is definitely cosmic ray hits. They are NOT completely blocked by the Earth's atmosphere and cause lots of hits on astrophotographs. That's one reason we generally take many subexposures when imaging a faint astro object (we're talking hours of exposure) and by using the appropriate averaging or statistical software, the hits can be eliminated.
The question about relative movement is straight-forward: everything EXCEPT satellites and meteors is fixed in space at the short time intervals involved in seconds/minutes/hours exposures and ALL the movement we see in a star trail image is due to the rotation of the earth. It's true that space is expanding and that objects in space have their own proper motion, but that is not visible on the "short" exposures we're talking about.
Constellations vary from star-size to much larger (Andromeda, our closest neighboring galaxy, is huge compared to the size of a star in our galaxy even though the stars in the Milky Way are millions of times closer. Even a ten-power binocular will show Andromeda as a significantly elongated smudge, while the stars remain pinpoints.)
Geostationary satellites do not move relative to an observer on Earth; they could produce a single spot, but they are too far away (26,000 miles up) to reflect that much light and (as far as I know) are not so far north as these hot spots.
Nonstationary satellites (200-300 miles up) have complex orbits and are best seen just after sunset or just before sunrise, when they reflect the most light from the sun but the sky is still dark enough to see them. Their motion is easy to see, usually taking just a few minutes to go from horizon to horizon. NASA has websites that predict when various satellites and the International Space Station will pass across the sky in any given locality.
Finally, what direction are the star trails going? Well picture yourself standing in an open field. The stars rise in the east and set in the west, right? So;
Looking north they go counterclockwise.
Looking south, they go clockwise.
And yes, the hot spots were cosmic ray hits.
Spend some time at one of your local astronomy club's star parties---you'll come away with a much better understanding of what's going on and maybe catch the astrophotography bug yourself!
Bert
www.astronomy-images.com
p.2 #5 · I shot a 50 minute star trail (15 3-min exp.) but what are these...
Every exposure having the same specks changes the picture (;-)) and suggests that you've got hot pixels in the sensor. To get rid of them, take some exposures ("darks") of the same duration with the lens capped. Then subtract these from the light exposures.
Cosmic ray hits can come from anywhere in the field of view and they mostly all originate from outer space with just a few from solar flares. They travel at very nearly the speed of light and consist of the nuclei (protons and neutrons) from hydrogen, helium, and a few of the heavier elements. My astronomy text says they probably come from dying stars (nova, etc).
Bert
p.2 #7 · I shot a 50 minute star trail (15 3-min exp.) but what are these...
I can confirm that these dots are ET and some of his gang - parked up and watching us from afar
I can also confirm that they have been reading these posts on *gww.fm.con and have delayed their arrival in order to enjoy the high levels of creative answers
p.2 #9 · I shot a 50 minute star trail (15 3-min exp.) but what are these...
It's hot pixels. Depending on the camera (New models are better) they start to appear after 5 minutes or so exposure on digital SLR's. I have done some tests on my cameras with the folllowing results :-
EOS 10D - Unuseable for exposures of more than about 5 minutes due to a combination of noise/hot pixels and amplifier glow.
EOS 5D - Ok up to 10-15 minutes.
EOS 40D - OK up to 20 minutes.
Hot pixels can be minimised by dark frame subtraction.
