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I woke up this morning with star trails on the brain. I'm not sure why exactly, but from the moment I woke up I pretty much knew I would drive back to Murray Hill and try some star trails. I'd been waiting for cooler, drier air to do this again and now I had it. The moon would rise at midnight and the sun would set at 7, so there would be a good window to try it. For a wide area of the central plains there were NO clouds to be found. I checked visible satellite and it confirmed there would be no clouds at all for this. I also checked water vapor and noticed some cool eddies on the back side of the major upper low to the east. The problem was the water vapor image wasn't that great as it showed there was some moisture aloft, even though there wasn't a cloud to be found. Anyway, more on this later. Just remember, it's pretty darn clear and crisp out and there are no clouds for hundreds of miles around. The above image at early twilight should show how clear it was. I had to bump the iso up to 1600 since I didn't want to grab the tripod and mess with it. I wound up with 1/6 second at F4. At full size it's not exactly sharp but I didn't care, it serves its point here. I wanted to go up to the top of Murray Hill and do the star trails but, well, screw that, it's spooky there alone! I went up there when I arrived(shortly after sunset) and walked around for 30 minutes in the cold before coming back down. On the way down it was getting pretty dark and this owl started to hoot. I knew then I would not return once it was completely dark out. I was walking down the trail thinking to myself, this trail back to the car would be damn long once I convinced my mind to screw with me!
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My parents wanted to see this spot and the stars, so they drove here too. They arrived about the same time I got back down from the walk. I imagine it was 30 minutes or more after the sun had set. They stayed there until I started the long exposure. Before doing the main, long exposure I wanted to be sure it was focused as well as it could be. I set it earlier but the camera/lens was still warm from being in the car. So, I wanted to get a good focus with my now cold camera/lens. I thought turning the ISO up to 1600 and getting a short exposure would work, but they kept looking soft. There seems to be a shutter length where the stars will look soft even if you are set at infinity properly. The above photo is at 1600 ISO and for 35 seconds at F4. 35 seconds will leave just a small streak and make the stars look soft. But, this photo does show something I wanted to mention. Notice the faint whitish coloring above and just left of the tree. It shows up the best in that area just left of center. You could see this belt of faint white light in the stars, mostly directly overhead. It's not the Zodiac light. I'm not sure what the name is for it, but I imagine even the slightest astronomy buff would know. It's not a cloud, I'm 100% sure of that. I've seen it before on very clear nights, but never took the time to learn what exactly it is.
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Ok, back to focusing. Since the iso to 1600 and short exposure wasn't making me satisfied, I had to try another way. I knew this way would work, but was trying to save my battery. If you do this and want to be sure your stars are sharp, just do a 2-3 minute exposure and view it full size. I was sharp all along, it just wasn't looking like it on the shorter exopsures, even viewing at full size. It's odd, but many times when I resize something down to web size(like the above 720x480 image) they look softer than they did viewed at full size. This sometimes happens even after sharpening. In this case it is probably again related to the size/length of the star trails. Viewed resized here they are much shorter/smaller than when i looked at them full size.
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Here is my 1 hour and 20 minute exposure. Not too bad I don't think. I could have done a lot better on the composure of it, but I'm still experimenting. I learned exactly where the north star was 40 minutes into the shot. I wish I would have at least had that in the frame. I feel stupid for not knowing how to find it(a line upward from the two stars making up the right edge of the scoop on the big dipper....or is that the small one, lol.....I need some work on stars). You can again see that white area going horizontally just above the center. Clouds weren't causing that, something in space makes that light. I'm sure I'll find out what by one of my nice readers? I learn a lot from readers of the site! Thanks in advance. A couple things learned from this outing. I think the most important thing learned is the value of using water vapor imaging along with visible satellite. Clear skies don't always mean the same thing. Hell, it was wall to wall sunshine and the ground was cool and very dry. But, more on this below. I learned it gets boring FAST in a parked car, in the dark, out in the boonies, waiting on a looooong exposure. I wanted to do the shot for at least an hour when I started it. I think I was 2 or 3 minutes into it when I was very ready to leave. I was like, how the hell am I going to convince myself to sit here for this long. I'm definitely dragging someone else with next time. I learned where the north star is for sure as I just said. I knew it had to be very high in the sky and just to the north, from my first time trying star trails. Oh well, I'll get it next time. I think I knew I wasn't going to get it when I took this shot anyway. Which brings me to the other thing I learned. The horizons are rather hazy and lacking stars. Composing the shot seems best if you can shoot up a hill or something. Well this is the case when using a DSLR with a 1.6 times crop factor and only 17mm for a lens. 17mm on my cam is just wide enough for storms, but really could be much more for the star shots. Next time I will try shooting from the bottom of those hills and pointing up them. Another thing was the huge number of aircraft in the sky. Holy cow. For some reason I was thinking they'd be more common to the south going into Omaha. I did not think there would be as many as there were either. They were everywhere and I quickly became concerned about them ruining my shots. They are moving quick enough that at ISO 100 they really weren't showing up. I thought I might have to stop down to 5.6 or more to make sure they didn't show up, but I was fine at F4. I think the last thing was the number of shooting stars. I think it was 6 of them I saw. I wonder what an average number an hour is, when not during some "event". Ok, on to what is probably the most important thing to look at when looking for the clearest of clear skies.
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This is the water vapor image for right when I got back home. The black arrow points to the location I was shooting at. Now this is water vapor, this is not a visible satellite image showing clouds. Believe it or not, pretty much the entire plains are under full clearing at this time. I looked at visible satellite before I left and can assure you that for the most part there wasn't a cloud to be found in ND, SD, NE, KS, OK, IA, MO. Looking at this water vapor image it is obvious though that there was moisture aloft. By looking at my stills above they should be able to tell it was pretty clear and crisp out. It was. It was plenty clear to do this. So, visible satellite can work well enough(remember....no clouds to be found anywhere in the neighborhood during this). But, what I was hoping for was one of those EXCEPTIONALLY clear nights. These are the nights where the stars really jump out at you. It can be rather surreal to look up at the night skies at those times. I've seen this kind of night sky many times heading back home after chases. I know where light polution is the cause and where it is not. I have seen this exceptionally clear stuff in this location before, so I know Omaha is not a factor. I did not see this kind of display tonight. It was very clear and the stars were very bright, but it was never one of those surreal events. I would have to believe I can thank the moisture aloft for that. It is strange to see this perfectly clear, blue sky and think, hey, it's probably still not clear enogh for "super" stars. Many of these upper storm systems will have this strong dryslot, or areas of strong drying associated with them. See the orange and brown colors across the south and southeast states here? Now that is some very dry air. Had that area been over my area then I would expect an exceptionally clear night. I'll try and post some comparison frames tomorrow when I can grab a visible satellite image so that you can see how the moist areas on the above water vapor image can be clear as clear can be. I hope no one is seeing this water vapor image I have here and thinking it was kind of cloudy when I took these. Think of the water vapor image and think of a very humid day...one with no clouds. The satellite can pick that moisture up and represent it like it does here, even when the visible says it is completely. Sorry for beating the dead horse here, but not everyone that looks at the site also looks at the weather stuff much. And hell, I look at that watervapor image and think clouds. I need an archived image now darn it. This will show what I'm saying. See below.
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Ok, here is the water vapor image at 2115 UTC(see the top of the image). 2115 UTC is 4:15 p.m. central time. This shows the moisture content, not the cloud cover. But if you want super clear at night you want that as dry as possible(red/orange shadings would be the best, but even as it was here it was rather crisp).
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Now this is the visible image at basically the same time, 2132 UTC(4:32 p.m. central time). You can see on the visible image there are no clouds in the area. The clouds over MN are slowly moving off to the north and east. So, using that water vapor image can be a valuable tool for finding the DRY clear skies out there. Here is a link to one source on the net: http://www.rap.ucar.edu/weather/satellite/ |
