Thursday, August 21, 2008

Astronomy and Sunsets

Whoopee! I saw Mercury last night! I have been trying for years to add that planet to my list but it always somehow eluded me. Once I thought I saw it but couldn't be sure. Since Mercury is always close to the sun from our vantage point, trying to catch it just after sunset and before it sets itself is tricky. This time I got a little help from Venus, so I feel more secure that I actually did see it. I also saw the "green flash" at sunset that I have heard about.

The conditions were almost perfect last night for seeing both of these wonders. There was haze but no real fog bank waiting on the horizon. The accompanying photos were taken the night before because, unbelievable as it may sound, I forgot my camera last night! I packed my binoculars and the spotting scope, a blanket to sit on, my hat, jacket because it would be chilly after sunset, quarters for the parking meter, but somehow forgot the camera. Oh well. The sunset was not a spectacular one as far as color goes, which was good. Beautiful sunsets are caused by smog and dust in the atmosphere, and of course clouds, and that sort of thing would obscure my view.

When I took these photos on Tuesday evening, I was just interested in the sunset, but when I got home I decided to check to see what stars were coming up and found that a very nice conjunction of the planets is happening this week. In the photo below, which was taken several minutes after the first photo, you can see Venus coming out. (It looks like a ball when magnified, but that is an artifact of my unsteadiness.) Mercury was just below Venus, but was not bright enough for the camera to capture it. And since I wasn't prepared, I didn't have my binoculars with me. So I didn't see it. I didn't even know it was there.

Last night, Mercury was just a little lower and to the left of Venus. Also Venus is magnitude -3.89 right now, and Mercury is -0.29—a can't miss it situation. (Magnitudes are reversed from what you would think, with negative numbers being brighter than positive numbers. It has to do with history.) Saturn at 0.83 was lower still and to the right, but not bright enough to break through the red haze. Mars at 1.71. never came out either even though it was higher and much further to the left of Venus. Sunset was at 7:31 pm, then Venus popped out and Mercury finally became visible at 7:55 pm.

My husband had told me about the "green flash" that can occur at sunset, but I never knew what it was I was supposed to be looking for. Thanks to Alex Filippenko and the Teaching Company's course, "Understanding the Universe: An Introduction to Astronomy" I learned that it is caused by the bending of light rays by the Earth's atmosphere and can occur at sunrise or sunset. Violet and blue rays, having short wavelengths, are bent more than the longer yellow, orange, and red rays. The green rays are in the middle. Blue and violet get scattered more and are absorbed by dust, the reds and yellows set first, leaving the green behind. That's an extremely simplified explanation. You can find out more than you ever wanted to know from the link above but a simpler explanation can be found here.

My flash was enhanced by a mirage and this is where things get really complicated. In this case, the rays are distorted, bending at different angles due to differing temperatures and densities in the atmosphere. What I saw (and now I wish I did have my camera with me) was a yellow sun melting into the water, breaking up into pieces with a green glow along the edge of the top piece. It was very slight and very brief. I probably would not have been able to catch it with a camera. Here is an amazing movie that is similar to what I saw.

Oh, and by the way, to protect my eyes, I did not really look at the sun until very close to 7:30.

1 comment:

  1. I tried to view the stars that night but AZ was full of clouds :-(

    Tonight we are having a major storm! Non stop lightning and thunder. It's very impressive.