...stationary dots in the image?

Below is a star-trail shot I took Friday night from 9:10 to 10:00pm at Dinosaur Valley State Park, Glen Rose, TX. This photo is a composite of 15 3-minute long exposures with a 30 second interval between exposures. If you look close or zoom in on the image you well see the segmented trails...each skip represents 30-seconds of relative earth movement to star location (can you find the exposure that I shot at 2 minutes instead of 3?).. Shot at ISO 100, shutter speed in bulb at 3 minutes, aperture stop f/8, on tripod. Combined in Photoshop using layer-lighten and the 16th frame on the top of the stack of layers was a shot with the lens cap on and layer mode darken. Shot with a Canon 30D and Canon EF-S 17-55mm f/2.8 IS USM lens.



View Original Size here to see the dots I'm asking about

I don't see how any light in the sky wouldn't trail so my only guess is that these could be artifacts genereated by the camera and/or lens?

-Roy

Nice work, Roy.

There is a better than even chance that I'm "all wet" here, but I'm wondering if you only get star trails from stars in our galaxy due to their “relatively” close distance. If I’m even in the ball park, the “stationary spots” might be galaxies that are so far away, that their relative viewing angle doesn’t change as the Earth spins beneath Polaris.

The situation I’m trying to describe is a bit like a train crossing directly in front of us, while another vehicle running parallel to the train, barely seems to move as it travels along on the horizon.

Great question! Maybe someone knows for sure. Best wishes. -Art

What Art suggests sounds reasonable. I suppose they could be satelites in Geosationary orbit, but then I wouldn't expect them to be that visible. Are they hot pixels?

Interesting,
J

They are most probably hot pixels. They cannot be any "objects" in the sky, since satelites, planets, galaxies and every other object would make the trails because of the Earth movement. Try 90 exposures for 30 seconds, mabye they won't be as visible as they are now.

I'd say hot pixels too, particularly with such long exposures.

Satellites in geo-stationary orbit could do that, particularly because the sun would be at a nice angle to give reflections off of them. Satellites general have massive flat panels for solar power and the like, so a reflection is possible.

The fact that I've never seen this type of thing before though, and that most star trails have been captured on film, I'd say hot-pixels is much more likely.

Great shot, although the multiple exposures has, unfortunately, made the trails discontinuous. You need film: open the shutter, have a nap, wake up a few hours later, stumble back to the camera and close the shutter... No hot pixels or heat noise!

Ross

yes its the 12th exposure

at F8 if dust were on the lens, it would not be in focus, even dist on the sensor would be dull, so any sharp objects in the photo must rotate with the camera, and earth, it might be possible that a 15 minute exposure would register a geosynchronis satalite, such as a space shuttle or space station or military satalites or even civilian satalites, out that far they are not in shade, so they will be constantly be reflecting light from the sun to us.

and hot pixels dont come up as white, they are red green or blue.

also satalites that are not in geosychronis orbit dont rotate with the stars, a satalite that is due north cant rotate in a small circle withoug using power and alot of it.

Oh boy...great discussion here. What about "dead" pixels? I think Greg is correct, aren't hot pixels colored?

Here's an interesting trivia question for those who haven't shot star trails. Which way did the star trail form? clockwise or counter clockwise?

-Roy

These are not external galaxies - they are too far away. These don't look like hot pixels (they're too big and you'd notice them in other images) or dead pixels (that would show up dark). Dust would show up as unfocussed dark circles.

These are cosmic ray hits -- I've saw them quite a bit when I took data at KPNO. Effectively, these things are coming in all the time, and they light up the sensor. You don't notice them in other images because either (a) the exposure time isn't long enough to capture them, or (b) the light in the rest of the image swamps their contribution. They're roughly evenly scattered over the area of the image; this makes sense to me.


I hope this helps.


Cheers,


Tony

Cosmic Rays eh? That's interesting...I'll need to look up this term

Maybe it can be solved using Einstein’s energy equation E=mc² Energy equals mass times the square of the speed of light

-Roy

My guess would be almost certainly hot pixels whatever -something to do with your sensor - your shot with lens cap on should tell you if it was your sensor - perhaps reshoot with cap on and a long exposure. The size of the dots could be because of the way you post-processed and stacked the pictures.

One of the dots clearly emerges from the tree in the image.
some type of noise pattern
I am highly doubtful of the cosmic ray idea...check your composites the dots would have to be in diffrent locations as they come and go.
Noise would most likely have some kind of randomness as well

intresting speculation to say the least going on here.

My hunch im going conspiracy theory
dat mus be sum-a den green aliens and der flyin saucers!

Yea, I see the one in the tree line and so now I'm going to look closer at each frame and get back with you all.

Thaks,
Roy

Art B:

It's an interesting theory, but thinking it through, I see some problems...

(1) You can only see stars discretely in our galaxy. Given that the nearest galaxy to us something like 2,000,000 light years away, you would only see it as a dot, not unlike a star.

(2) Your analogy to the moving train implies that the object viewing the nearby train and the faraway train is stationary relative to both moving trains. But the problem is that a photographer on earth is not stationary with respect to distant celestial objects; in fact, he or she is moving a lot faster relative to any object in the sky than any object is moving relative to the earth, albeit the movement being rotational rather than linear.

What we are seeing in the motion of the stars is the earth's rotational motion, not the movement of celestial bodies toward or away from us. Even though the relative change in position of celestial bodies as we see them here on earth would clearly fall into your "train and distant vehicle" analogy, the motion trails captured here are almost entirely a result of the the earths rotation, and not the motion of objects through the heavens.

Again, I may be out of my element here as well, but the dots seem to me to be either camera artifacts, or perhaps satellites in geosynchronous orbit. Either way, the dots must be synchronized with the earth's orbit, rather than independent of it. A camera artifact or geosynchronous satellite meets that limitation.

Arka C.

Arka C:

On item 1: I think we are in exact agreement... i.e. local stars and distant galaxies would both appear as dots... relative motion not being a consideration.

On item 2: I also agree with your "stationary vs. moving" analysis... i.e. what is moving and what is stationary is all a function of the relative coordinate system that is choosen as the reference point. That said, because two of the three objects in question are very close to each other, I can't help but wonder if it still might "seem" to work over this relatively short period of time.

Great discussion. -Art

I once had a high school student neighbor who was taking photography in school. He had an assignment to do a picture with the theme of "stars and stripes" and he didn't want to do a picture of a flag like everybody else was doing. He'd seen one of these, so he asked if he could borrow my tripod and set up to do it in my yard (we lived in the country, and there weren't so many trees in my yard.
He did an excellent picture of the stars making stripes, then doted each stripe with a star at the end after a small lapse. He got a nice print made.
Teacher gave him an F on the work because "it's not what I had in mind"
He should have received an A+ for being creative and thinking of something original!

The earth is spinning at a rate of 30 kilometers a second.
the farther away that object is the faster it must travel in order to remain relative in position to the earth. think of a fan blade the core of the blade is spinning slower than the outer tips.

So IF we were to presume it was a star its distance would be at least 2.3 light years.... In order for the object to remain in the same place in the sky its speed would have to AT least more than the speed of light...I would be intrested for someone to do the math and tell us the exact speed that object would have to be.....

Maybe its dos durn aliens messing with there jump drive running huge 2.3 light year wide arcs of travel around the earth.....kinda the equivilant of us doing donuts in a parking lot :-p


So no way its a star or celestial body.
Satilites, or Camera noise.

As for radiation the only type of radiation i know of that would be able to pass through the earths atmosphere and into camera would be a neutrinos, Neutrinos are extremely hard to detect as they rarely react with anything....many pass through the entire earth without interacting with an atom once. The worlds largest photo sensor is located in alaska to pick them up...its measured in kilometers. So i doubt your lil camera caught nuetrinos :-p

Ohh and MKweaver....
I hope you took the case up with the princable and district or whoever else above the teacher, unless the teacher stressed a patriotic American based image focusing on FLAGS he had no right to grade your child as he did. That kind of judgment especially on something that is a ART and not a science smashes creativity.

it goes counter clockwise, thats why i knew it was the 12th exposure and not the 4th exposure

looks like I found the answer.. dropped the image into this new enlarging app i just got, and it was able to give us a better look.

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

News flash, every single exposure had the same light spec. Humm...do cosmic ray hits happen from the same source? I think these are from my camera.

And, the 2 min. exposure was the 4th exposure, not the 12th, because yes, the trail moves counter-clockwise.

-Roy

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