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Wednesday, June 27, 2012

Mid-Summer Sledge Hammer Sun Compass

Can you find the directions of the compass with only the sun to guide you? Did you know that midsummer, it's a little bit different from the other seasons?

I used the sledgehammer as a gnomon. (Isn't that a great word? It's the upright of a sundial). The reason this isn't a sundial is that I'm not trying to tell the time. In fact, I used the clock to note when to take the pictures- one every hour all day when the sun was high enough above the trees to make a shadow.

Then, I created a composite. You can click it to make it bigger. I recommend you do so.

Now, for the interpretation. The yellow line is the actual east-west line (pretty close- this isn't a technical drawing).

The first thing you should notice is that the shadow cast at 2 pm is the closest to pointing straight north. What's up with that? That's the easy answer. First of all, we are in Daylight Savings Time, which pushes the clock time of 1 pm to be most like noon sun time. But there's another thing going on that makes the shadow almost an hour off where I live. I'm in western Michigan, but I'm still in the Eastern Time Zone. In fact, I'm almost as far west as you can be and still be in Eastern Time. There are parts of the Upper Peninsula that are farther west and still in Eastern Time. So, the effect of that is to make the 2 pm clock time the closest to noon sun time. Got all that?

So what? So, if you are where I live and want to find north by your shadow, you have to make mental adjustments, or wait till almost 2 pm to see that north-pointing shadow.

Now for the other goofy thing! In the northern hemisphere, the sun is generally in the southern sky. That's why a shadow is cast at noon sun time. For most of the year, in the early morning your shadow will point slightly northwest, and in the late afternoon your shadow will point slightly northeast. So, to find true west or east, you just adjust a little bit.

At the equator, your shadow at noon should just be a spot around your feet equal to the largest diameter on your body.

However, at the summer solstice, the sun is at its farthest point to the north. This is extreme enough to overcome that generally southern track. Note on the picture that the shadows at 8 and 9 am, and 7 and 8 pm are all beyond the E-W plane. So, at this time of year, if you are walking directly into the sun in the evening, west is just slightly to your left. For most of the year, west would be slightly to your right.

OK, I'll stop now. If you are like my friend Marie, she is good with all this up until the part where I add any information beyond "the sun is in the sky." Well, I'm kidding. She knows it comes up in the east and sets in the west.

What can I say? She's glad I can find my way with the sun!

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vanilla said...

"...up until the part where I add info..." Good one.

I follow this; yet it rekindles my annoyance with the fact that we essentially have "double daylight" time due to the fact that we really should be in the Central Time Zone. Or not have daylight time.

Chuck said...

I recently exchanged e-mails with Vanilla about sun declination/length of day and difference between solar and standard time/equation of time. The analemma explains this well. You can thank Wm Durand (founder of GM) & his associates for convincing the Michigan legislature to the Eastern Time zone so that they could be on the same time as their New York bankers. We really are the auto state. :)

rainfield61 said...

You are so good.

Ann said...

After reading all of this it tells me that I am in big trouble if I ever need to find my way by this method :)

Sharkbytes said...

vanilla- It doesn't bother me. I like the long evenings

Chuck- Makes sense for the time it was chosen. I don't mind because I'm not a morning person.

rainfield- well, I don't know about that, but I'm handy to have around in the woods

Ann- You are funny! I think you'll be in good company with Marie.

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