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Headshot of Bill Nye - Updated

Let’s Reckon Time Together

Observe the Shadow of Our EarthDial

Posted by Bill Nye

20-03-2013 24:51 CDT

Topics: Planetary Society Projects

EarthDial Live Cam

Our EarthDial is up and running, or up and reckoning. We encourage anyone within a mouse click to build one and send us images.

As you probably know, there are now three sundials on Mars. We call them the “MarsDials.” Their original and fundamental purpose is to serve as test patterns for the cameras on the Spirit, Opportunity, and now Curiosity rovers. They each feature an upright post right in the center of the pattern. The post casts a shadow, and the color of the Martian sky reveals itself. If you’ve never done this, look closely at a terrestrial shadow as it’s cast on something very white, like a piece of paper or a freshly laundered white shirt. Along with the gray, you’ll see a tinge of blue. It comes from the Earth’s blue sky. We didn’t’ have a word for it, so I made one up: “cirulescence,” a tinge of blue. Scientists, like our own Jim Bell, then can infer the contribution of the orange Martian sky to the colors recorded of the local Martian rocks. We did not have a word for this either, so I call it: “orangidescence.” (At first, I spelled it “arrangidescence,” but I’ve come to prefer the former.)

Since we had shadows being cast on Mars, I suggested it be a sundial… I admit I was quite enthusiastic about it. Steve Squyres, the Principle Investigator on the Spirit and Opportunity missions, made the call, and the MarsDials were created. He received the Society’s Cosmos medal a few years ago, for his wonderful leadership of the project.

The EarthDial project was born in 2004, and we’re bringing it back again for the Curiosity mission. It’s a sundial visually reminiscent of the MarsDials, but exactly ten times as big. We encourage you to set up your own EarthDial, rig up a webcam, and post the images. In the coming weeks, we’ll coordinate the EarthDials from around the world, just as we did for a few years after the Spirit & Opportunity landings. It’s a remarkable project that can engage individuals, classrooms, or entire schools. The price of webcams has come way down in recent years. So, we’re hopeful that several readers of this blog will give it a try.

Our first EarthDial of 2013 is built on a plastic table. In just these first few days, I can tell that we’re having problems with the thermal expansion and contraction of the dial table. In the coming days, we’ll work on that issue, and just as important we’ll add some artwork, what’s called “furnishing” to the dial surface. So, stay tuned.

As I write this, the 2013 vernal equinox is upon us. Observe the shadow of our EarthDial. Observe and note the shadow of any vertical post. The tip will follow a straight line (with a tiny variation). The insight one can get from the diligent observation of sundials is astonishing. Take a look at the pages here, many of which are still serviceable from eight years ago. Let’s reckon time together and learn a bit more about our place in space.

See other posts from March 2013


Or read more blog entries about: Planetary Society Projects


Barin: 03/21/2013 11:29 CDT

Hey Bill! Good to see the EarthDial is back! Don't know if you remember, but my middle schoolers built ED21 down in Lecheria, Venezuela. Good times! Back in the USA now and want to build another. Definitely will let you know! BHB

Chris Campbell: 03/23/2013 09:23 CDT

What a coincidence Bill ... Just today I finally cracked open my copy of "Postcards From Mars", the coffeetable book of MER photography by Jim Bell, and read your foreword that mentions the MarsDial. And thanks for your voice on my answering machine (I won the contest on Planetary Radio about a month ago). It's a riot!

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