Yesterday I presented readers with a problem – Can you tell the approximate time of day an image was created in Google Earth? Using the image above of Cherrydale Shopping Center in Greenville, I pointed out some clues and some strategies for making a guess. Here’s another, sure-fire way of figuring out the problem…
First, visit the website for the Royal Observatory at Greenwich, England. They’ve got an excellent tutorial on how to create your own sundial. However, what you’re really after is the sundial template JPG, which I have posted below…
What you need is the URL to that image, which I’ve conveniently pasted below:
The next step is to open Google Earth and zoom in fairly close to your target area. Make sure that you have north at the top of the screen. Pick out a nice, clear shadow, preferably one made by something tall and skinny like a pole or sign. Click on the Add Image Overlay button. In the box next to “Browse” paste the URL for the sundial image.
Once the sundial image appears, set the opacity of the image about halfway so that you can see the sundial, but can also see what’s on the map underneath. Position the image so that the lines of the sundial converge on the shadow you selected. You should then be able to read the time of day on the sundial. This will tell you when the image was captured.
As shown in the illustration above, this particular image was captured at about 9:00 am.
This is also fun to try with large landmarks, such as the CN Tower in Toronto, Canada, the Eiffel Tower, the Burj Dubai, and other tall structures.
Once you have looked at several structures from around the world, look back at the length of the shadows. Does latitude have an effect on the length of the shadow? There’s lots of science you can work into this lesson.
UPDATE: As I think about this, I doubt it would work for the southern hemisphere. I think you would have to create a graphic that points south. You can’t just rotate the existing image. You would need to do a horizontal flip.