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omega sunrise


omega sunrise
Photo Information
Copyright: Bob Harrison (BobH) Silver Star Critiquer/Gold Note Writer [C: 40 W: 8 N: 192] (650)
Genre: Landscapes
Medium: Color
Date Taken: 2002-09-29
Categories: Sky
Camera: Olympus 700C UZ
Exposure: f/8, 1/1000 seconds
Details: Tripod: Yes
Photo Version: Original Version
Theme(s): Sunrises, Sunrise & Sunsets [view contributor(s)]
Date Submitted: 2007-12-07 3:09
Viewed: 12292
Points: 6
[Note Guidelines] Photographer's Note
This post is an interesting complement to my recent "ameboid sunrise" composite. It was taken from a different spot in my town a few km away, but also looking unobstructed over the open Atlantic Ocean. This one is not as aesthetic, but is still quite unusual, and a reminder of how nature's oddities are often hidden in plain sight.

This phenomenon is called Daruma Sun in Japan, and an omega sunrise elsewhere, after the obvious resemblance of one of the stages to the Greek letter omega. I've seen this numerous times, have recorded several, and have spent some web research time trying to understand what seems truly bizarre at first. A number of single frame images of omega suns can be found on the web, but only one not so clean depiction of the time course of the event, so I did one myself.

In a nutshell, this image shows an inferior mirage (meaning the inverted image is below the erect image) due to refraction through air layers close to the ocean surface. Any detailed description of the physics of the refraction is a bit more than I want to put in a TN note, so I'll instead provide links to what I found to be the best source of information- several pages by Andrew Young.

Young's pages include a helpful simulation (http://mintaka.sdsu.edu/GF/explain/simulations/inf-mir/Omega.html) that matches well what I've recorded here. The strangest feature of this image is the apparent boundary above the horizon, called the "fold line" and described by Young (http://mintaka.sdsu.edu/GF/mirages/Wollaston.html) in both historical and current context.

A couple of pieces of Young's writing are just right for extraction here. In reference to the temperature driven density gradient which is responsible for the phenomenon, he wrote, "...as we approach the surface, the temperature increases more and more rapidly... Below the fold line, the rapid change in temperature gradient with height makes the atmosphere act like a positive, cylindrical lens, which forms a real, inverted image: the inferior mirage. This lens is located near the apparent horizon. The power of this lens is proportional to the curvature of the density (or temperature) profile."

Also, "...the fold line appears at the altitude where the focal length of the atmospheric lens approximately equals the distance from the eye to the apparent horizon. The lower the eye, the shorter is the distance to the horizon, and the closer and more powerful is the lens at the fold line. This makes the mirage look bigger."

I've found it nearly impossible to be sure I was seeing the effect until viewing images after capture, likely because of the increasing light levels and lack of prior eye adaptation. I suspect that the sunset version would be easier because of the decreasing light levels, but I've never seen an omega sunset.

I hope this is a helpful introduction to an intriguing atmospheric effect. If you want to capture your own images like this, Young's writings give some guidance about what to look for. Beyond that, all you need is the willingness to look carefully and a camera to record what's there.

Tech notes- all shot at max optical zoom (35 mm equivalent focal length of 380 mm) with 3x digital zoom, hence not the best clarity. Duration was 68 sec from first to last frame. No modification beyond minor brightness and contrast adjustment and the obvious cut and paste in PS. Sorry about the black banding top and bottom- I had to cheat to get the 250 pixel vertical minimum.

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To papajoehermit: appreciation on TNBobH 1 04-29 05:41
To Ric: thanksBobH 1 12-17 10:32
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Critiques [Translate]

  • Great 
  • NinaM Gold Star Critiquer [C: 773 W: 3 N: 1157] (4077)
  • [2007-12-07 9:04]

Thank you once again Bob, I feel privileged to see such photos with such great notes. Very interesting, I find it quite fascinating. The photos demonstrate very well your comments and add to it. It is clear, sharp and every time I read your notes, I learn so much. Thank you to share your knowledge and "savoir-faire" on TN. This one is captivating.

Francine

Dear Bob,
Interesting phenomena you show us in these sequential photos. The explanation is very illustrative and really helps to understand the optical effect.
Note: I also check your gallery and I can see that you discover a lot of interesting things here in Maine.
Thanks & Regards
Ricard

Belongs in a scientific journal. As lovely as it is, it can't be appreciated on TN.

JoeG, Louisville, KY

Hi Bob, How did you did that?

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