Thursday, October 30, 2008

Just asking because we really don't know

Is there any way to know whether or not this picture was taken at sunrise or sunset?

Does the difference in temperatures (colder at dawn than at dusk) or moisture content in the air do anything to visibly alter the color spectrum where one could tell by the naked eye when this picture was taken?

With a front moving in this afternoon, it should be a spectacular sunset this evening.


Ohioan@Heart said...

Assuming you are asking in a sense that means we should ignore horizon cues that would tell us east vs. west, then the answer is no. Not by the naked eye.

Now could it be told, in any way? From a photo? I don't see how. If the person and some instrument were there live? I think the answer is, yes. At least in principle.

The relative motion of the surface of the earth to the sun would produce a TINY doppler shift in the light. Slight blue shift at dawn, red shift at dusk. So if the sun is visible I think the aborption lines in the spectrum would make this worth trying. If the sun is already down, then alhough the same shift is present in the general spectrum, and so the position of the peak of the black body curve must shift, I think it would be too small to be reliably measured.

Seems like just standing there and seeing if it gets brighter or darker would be way easier...

Dean said...

O@H, I was hoping you would chime-in on this one. Thanks!

OK, some of that was a little over my head (black body curve) but I get the general drift.

My scientific method would be to look at a picture of a sunrise/sunset and ask myself whether it made me feel like having a cup of coffee or a cocktail. ;)

Ohioan@Heart said...

Almost didn't post that answer.

Glad I did. If you want to understand the black body thing, go to wikipedia, it's a great explanation (with more equations and details than you'd really want).

The coffee/cocktail method won't work for me - I'd always take the coffee. Now coffee/beer... That's a whole 'nother kettle of fish.