The Elemental Incremental Sunrise

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The alarm rang at 05:30 this morning. What a drag! Eunie had to get up to go the airport for something. I poked my head out of the front door. Hmmmm . . . First time in a week that the sky was clear in the East at this time of morning. I grabbed by camera and tripod and staggered down to the edge of the harbour about 10 metres from my front door.

This shot, taken at about 05:45 needed a ten second exposure. That’s why the water looks so glassy:

05:45 Sunrise at my house in Madang, Papua New Guinea

You can clearly see the lights of town. The sky appears almost completely blue, because the sun’s light is only striking the upper layers of the atmosphere, which is relatively clear of dust and other nasty stuff that causes the red colours.

At about 06:00 things were beginning to change. This exposure was less than a second, so you can see wavelets on the water. Also, since the sky is much brighter, you can barely see the remaining lights in town. The sun’s rays are coming into the lower atmosphere now, not quite at cloud top level, but low enough to pick up red-scattering dust close to the horizon:

06:00 Sunrise at my house in Madang, Papua New Guinea

Now, at about 06:15 the sun is beginning to catch local clouds and light them up. Light is coming straight through the troposphere, where most of the dust is, so we’re getting as much red as we’re going to get:

06:15 Sunrise at my house in Madang, Papua New Guinea

All three images appear to be about the same brightness. However the actual light available in the first shot, during which I could barely see a bluish glow in the sky, is probably several hundred times dimmer than in the third one, which was nearly as bright as day. I can tell that from the shutter speeds. They ranged from 10 seconds down to about a tenth of a second. If my rusty old memory serves to do the numbers that’s about 8 f  stops which come out to something like 250 times more light on the third shot than the first. (No, wait. Forget that. I remember now – it’s a logarithmic  scale. There was probably several thousand times more light for the last shot than the first. This is what modern digital cameras do to you. They make you forget the fundamentals. Just twiddle the knobs and buttons until it looks okay on the little screen.)

If I’ve got it wrong, leave a comment. I love to be publicly humiliated. I’m funny that way.

It never fails to amaze me what one can learn from simple observations of the world around us. The beauty is a bonus.

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4 Responses to “The Elemental Incremental Sunrise”

  1. magnus Says:

    its due to rayleigh scattering.
    http://en.wikipedia.org/wiki/Rayleigh_scattering

  2. MadDog Says:

    Thanks for that, magnus. It’s good to be reminded of the terminology. It’s been a long time since university.

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