A few months ago, I provided the link to kuriositas’ 10 Spectacular Radio Telescopes Around the World. I’m providing the link again so you can read about the Nobeyama Radio Observatory, home to the 45-meter telescope shown in the image above. I’d tell you more about it myself, but I have a pounding headache and just don’t feel like it.
Ancient Measuring Well, Aswan, Egypt. Image credit: Bob Sacha/National Geographic
Today’s post celebrates the arrival of the June solstice. The image above shows a measuring well in Aswan (Syene), Egypt. Aswan is situated such that at high noon on the solstice, the sun appears directly overhead. If you stand a stick straight up in a pile of sand, you won’t see its shadow. If you lean over a well, you won’t cast a shadow on the water because the sun is directly overhead. If you repeated this behavior the next day, and the day after that, and so on, you would see slivers of shadow appear and gradually grow larger as the days passed.
It was just this observation that inspired Eratosthenes’ legendary calculation of the Earth’s circumference. Eratosthenes was already in the habit of measuring the shadows cast in his hometown of Alexandria at noon on the solstice. When he noticed the lack of shadow in the southern city of Syene at the same time of day/year, he realized he could use the angle of the shadow in Alexandria to calculate the angle between the two cities as measured from Earth’s center. A few applications of geometry later, he arrived at a decent estimate of Earth’s circumference.
Was there any doubt that I’d be looking for a wallpaper featuring yesterday’s Transit of Venus? I’m happy to report that we didn’t have to rely on SDO images (as spectacular as they are!) to view it. We had mostly clear skies, warm evening temperatures, and lots of viewing equipment. I had my doubts as to whether we’d be able to view it with the naked eye—that is, the naked eye with protection—but it was easy to see through eclipse glasses. I used a solar projector made with a pair of binoculars. That was a last-minute project, but it made beautiful images, complete with cloud cover, sun spots, and Venus. We attended a public viewing event for part of the evening, courtesy of the DNR, Stonebelt Stargazers, and the Indiana University Astronomy Club, so we also had some excellent views through 8″ and 10″ telescopes. You can see a few photographs, including one from the solar projector showing Venus against the backdrop of the Sun, on my flickr site.