Another Shot At The Sky

Last night’s photography has been “Topic A” with me today. After a disappointing astrophotography session Saturday night I was upset that Sunday night would be clouded out. Sometimes even I am happy to be wrong!

The clouds held south. As astronomical twilight set I carried my camera, tripod and intervalometer out onto the front yard.

night-sky-may-20-2012-hamden

Last night’s photography has been “Topic A” with me today. After a disappointing astrophotography session Saturday night I was upset that Sunday night would be clouded out. Sometimes even I am happy to be wrong!

The clouds held south. As astronomical twilight&#185 set I carried my camera, tripod and intervalometer out onto the front yard.

I make noise when I’m outside at night. I am still a city boy at heart. I don’t want any curious animals scaring the crap out of me.

Welcome to the digital age. Once the clicking began there was no need for me to be outside. The camera was driven by the intervalometer taking shot-after-shot.

With some sophisticated, but free, software I was able to combine my shots for the equivalent of a nearly 17 minute exposure! That’s why you see above.

Some shots needed to be thrown out. A few airplanes flew by. In a few more I picked out the faint signature of polar orbiting satellites flying by. All I wanted was natural points of light.

I used a much more sensitive lens Sunday than Saturday and it paid off! The sky was full of stars–thousands I’d guess.

One of my Facebook friends, Joe Roberts, estimated I was able to see down to magnitude 12 or 13. The naked eye can see around magnitude 5. That’s impressive considering no telescope was used.

I’m going to have to examine the image closely. Joe says there are at least a few galaxies visible. There are some ‘fuzzy’ stars which will have to be identified.

I’m disappointed in some distortion toward the edges of the frame. What should be tiny dots of light look triangular. Probably some weakness in my lens.

I will try again. Is it possible to get hooked on this without spending more money? Please, say yes.

&#185 Astronomical twilight is the time when the center of the sun is between 12° and 18° below the horizon. From the end of astronomical twilight in the evening to the beginning of astronomical twilight in the morning, the sky (away from urban light pollution) is dark enough for all astronomical observations.

Astrophotography: Anyone Can Do It

Meanwhile the Earth is spinning on its axis. Like the rotating restaurant on the top of a cheesy hotel we are constantly pointing in a different direction. That creates a photographic problem and opens a photographic opportunity!

A few nights ago I pulled “Clicky” out and shot the night sky. My intention was to produce a time lapse as the stars rotated by (at the bottom of this entry).

As I showed the video one thing became obvious. Many of those who saw it didn’t realize they’d see that effect from a camera in a fixed position. We’ve become out-of-touch with the nighttime sky which no longer is as visible nor has the importance it did to our great grandparents.

Stars are very, very far from us. The closest star (other than our own Sun) is Proxima Centauri which is about 25,260,733,353,600 miles away (that’s 25+ trillion miles)! Others in the visible sky are thousands or even millions of times more distant. That keeps our view of stars reasonably constant.

Meanwhile the Earth is spinning on its axis. Like the rotating restaurant on the top of a cheesy hotel we are constantly pointing in a different direction. That creates a photographic problem and opens a photographic opportunity!

The opportunity is time lapse. What my little movie shows isn’t stars moving, but the effect of the Earth rotating&#185. Aiming at any single point in the sky reveals stars passing by. They’ll return to about the same point 24 hours later.

The photographic problem is the same one faced any time you try to photograph something in motion: blur!

Because stars are dim the only way to photograph them is to keep the shutter open a long time and allow more photons to hit the camera’s sensor. The longer the shutter is open the farther those stars move. The result is streaks across the sky, not points of starry light.

Sophisticated astronomers (aka – not me) solve this problem with clock drives. Their telescopes and cameras move in exactly the opposite direction as the Earth. The effect is to hold the stars still.

There are simple mechanical devices that do exactly the same thing. I’ve got a little wooden wedge with a hand turned screw which allows my camera to take long star exposures with impunity.

Nowadays the easiest way to eliminate the blur is with a software assist.

When I shot my time lapse I took over 400 images one-after-the-other. Each was a single second’s look at the sky. Using a program called DeepSkyStacker I combined those images and restacked them eliminating the effect of Earth’s rotation.

As a bonus DeepSkyStacker looks at specially shot blank frames to understand my specific camera’s weaknesses and counteract them!

The resulting photo is the equivalent of an eight minute plus exposure–though digitally made superior.

I’ve taken a small piece of it an placed it at full resolution at the top of this entry. Just below it is the full frame (though not at full resolution). These shots, compilations of over 400 separate photos, show stars I couldn’t see with my naked eye.

It’s all very heady stuff and amazing to me. It’s not just that these techniques are available, it’s that they’re available to anyone for free and easily used with cameras a lot less sophisticated than mine.

&#185 – Here’s re-tweaked version of my time lapse nighttime sky movie from a few night ago.