Rockin’ ’round The Big Dipper Clock

The need to know the time is a trait that goes back to the early days of civilization. Photo: Petar Milosevic

Does anyone use a watch anymore? Unless it’s a Rolex for show, it seems time keeping has migrated to mobile phones.  Not that I miss the good old days. I enjoy how ingenious we are, constantly re-inventing and re-packaging old ideas.

Time-telling is as ancient as the stars.  Planting, harvesting and important civil and religious ceremonies were tied to calendars based on the movements of the sun, planets and particular stars and star groups. If you’re in a retro mood and willing to extricate phone from palm, how about a mind-meld with the ancients the next clear night?

Before you go out, visit this site and make yourself a star clock. This simple device, which you can assemble from two pieces of paper, lets you tell time using the Big Dipper. Here is a direct link to the Adobe Reader pdf file to print out the star clock. If your computer doesn’t have Adobe Reader, you can download a free copy here.

This simple star clock uses the Big Dipper and polestar to tell time. Turn the outer dial so the current month is at the top. Then turn the inner wheel to match the Big Dipper’s position in the sky (as you face north), and read the time off to the side. Remember to add an hour for daylight-saving time. Photo: Bob King

You can treat the two Pointer stars at the end of the Dipper’s Bowl as an hour hand on a clock with the North Star at the center. As the Earth turns, the Big Dipper describes a circle around the North Star every 24 hours, or one rotation of the Earth. From the northern U.S., that circle never gets cut off by the horizon and so the Dipper never sets.

The star clock is a fun little project that even I could put together in under 10 minutes. It’s the lowest of low-tech and would make a fun exercise for the classroom. There’s even a paperless way which I’ll share tomorrow after I check out how it works tonight. Stay tuned.

(Psst … the paperless method worked out great. Here’s the link.)

11 Responses

  1. les

    Hey bob…ive been seeing alot of chemtrails when i look in the sky..what are they and why are they doing it?? I figured u might know. Thnx

    1. astrobob

      Hi Les,
      Those are contrails created by condensing water vapor in the exhaust of jet engines. They’re extremely common. Chemtrails are another bogeyman concept.

  2. Lynn

    Hi Bob

    I just came across the nasa/jpl space calendar website, that’s the first I have seen it, and on it there is a list of asteroids and giving you details of their closest approach to earth or saying it’s a near earth flyby, and I was wondering if they are at the closest approach to earth etc why are they not on the JPL website for close approaches, hope you can help Bob. Thanks 🙂

    1. astrobob

      Not sure I can answer your question but I’ll try. The space calendar ( has been around a long time and lists lots of predicted asteroid and comet close approach dates plus meetings and other calendar items. Some of those Earth-flybys are relatively close like 2012 FH58 on April 3 at 837,000 miles; others like 2829 Bobhope are much farther – 204.6 million miles on April 9. My guess is they’re not on the close approach page because their close approach distances are not exceptional. If you go through the list, you’ll see many of the asteroids are named, which means they were discovered some time back and their orbits are well-known.

  3. Syed S

    I noted the similar trend about watches. I’m only in my 30s, but growing up as a kid, having a watch on your wrist was very ‘cool’. It was something that you could have, on your person, that would actually tell you something. Unique for back then and that was the 80s. In the 90s came pagers, and then advanced pagers that could tell you the weather and a few lines of news! Amazing. Then cell phones came along in earnest, hit their stride once they went digital and the rest is history. But you still cannot BEAT the convenience of a quick glance at the wrist for checking the time.

    1. astrobob

      Hi Syed,
      I like the quick glance, too instead of reaching into a pocket to dig out my cellphone.

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