What's That Light in the Sky ?

[Bill Jobes]

Last evening, my son called me out to see something unusual in the night sky.

Close to the horizon, there was a tiny bright light that was rapidly changing colors. This was much more than a 'twinkling star.' Even though it was only a pinpoint of light, the colors were visible to the naked eye. Through binoculars, though the light was tiny, I could make out what looked like a bright white center, with red and green on the sides. Since it was stationary, I surmised it was perhaps a helicopter with a strobe and red and green navigation lights in the far distance.

I decided to take a long shot, literally, and see if I could capture an image. I quickly set my Nikon D300 with the 600VR and 1.4 TC on a monopod and attempted to capture the image. Needless to say, this was a very iffy, shaky effort. I did, however, manage to get a few images.

When I uploaded them to my computer, the light was still a tiny spot on the screen. Imagine a pixel or two.

I enlarged it as much as possible to see some detail, with Capture NX 2, and then Photoshop CS3.

There were the colors ! Spectacular, and somewhat different on each of the images.

I'm posting a representative image here.

Camera settings were 1/640, 7.1, and ISO was 0.7 EV over 3200.

Unable to determine the source, I called upon Dr. Roger Clark, BPN's own Moderator of Digital Photography Workflow, and an internationally recognized space scientist and photographer, for his thoughts on what I had seen.

He generously permits me to quote his comments here:

First, before seeing the images, Roger said:

"This sounds like a common situation. All objects close to the horizon are stretched out into a small spectrum due to the variation of the index of refraction of the atmosphere with wavelength. Large objects, like a planet or the Moon have many overlapping spectra so the effect is usually not seen. But stars, being point sources are stretched into a nice little spectrum. Then add a little turbulence and the spectrum dances around giving many colors."

Then, after reviewing the images, he replied:

"Those are great examples of starlight being split into a spectrum and
distorted by atmospheric turbulence!"


At Roger's suggestion, I am posting the image and the account of the adventure.

Just in case you've wondered about those strange colors, blinking away on the horizon ! :)

[Roger Clark]

Hi Bill,

To add one more piece of trivia, when looking at something outside our atmosphere, like the Moon or stars near the horizon, the equivalent atmospheric thickness is about 35 (where viewing straight overhead =1). With that much atmospheric path, a little turbulence goes a long way to messing up an image.

Roger

[Harshad Barve]

wow , Bill thanks for posting this and Thanks to Roger also

[Bill Jobes]

Thank you Harshad, and thanks, Roger, for the valuable additional comment !

[Jeff Parker]

So THAT'S why stars sometimes shimmer and change colors! Very cool, thanks for sharing.

[Michael Pancier]

which also explains why we get amazing hues during the golden hour

[Roger Clark]

which also explains why we get amazing hues during the golden hour

Michael,
Golden hour color is a different effect, caused by two things. The Rayleigh scattering that makes the sky blue also scatters away the blue wavelengths leaving sunlight more red. The effect is small when the sun is overhead but becomes greatly magnified where the sun (or moon or stars, etc.) are near the horizon where the atmospheric thickness is 20 to 30+ times greater. Second, dust in the atmosphere over that great path length, when the sun is low, absorbs blue light more than red, making the light redder.

We'll probably get some redder sunsets this spring and summer because of the fine dust from the Iceland volcano plume.

Roger

[Arthur Morris]

It sorts of looks like a colorful kidney stone....:confused: