How to Make a LEGO Sundial

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Recently, we have been working on how to read the time. My son curiously asked, how did people tell time before the clock was invented? 

The sundial is probably the oldest instrument that people used to tell time. All you need is an upright stick positioned in the ground with small stones to indicate the time. 

LEGO Sundial Outdoor

But why not go fancy and make a LEGO sundial? By using LEGO bricks to build the sundial, you add engineering into the project. 

Start with the LEGO sundial outside in the sun as early in the day as possible. You want to maximize the number of times in which you can mark each hour throughout the day.

Make a LEGO Sundial

Materials:

  • LEGO blocks
  • LEGO baseplate
  • Dry-erase marker

Instructions:

  1. Determine where the middle of your baseplate is by counting the studs.
  2. Start building the gnomon, the part of the sundial that casts a shadow. We used 2×2 LEGO bricks to make ours. Tip: I recommend putting a small plate down where the middle of the baseplate is to mark the spot. A few times, the gnomon got knocked over, and we had to recount the studs every time to find the center.
  3. Choose a time to bring the LEGO sundial outside. It’s best to start at an exact hour. For example, 9:00, 10:00, etc. versus 9:15 or 10:15.
  4. Choose a good, sunny spot for the LEGO sundial. Make sure the spot is exposed to the sun all day with no shadows nearby.
  5. Mark the time on a LEGO block. Again, we used a 2×2 block.
  6. Place the LEGO block marked with the time where the gnomon casts the shadow. 
  7. Repeat every hour as many times as you can. 
  8. Place the rest of the LEGO blocks directly across the sundial to complete the entire “clock.”
LEGO Sundial Hour Numbers

I know what you are thinking – I need to remember to go outside every hour to mark the sundial? Don’t worry, that’s what technology is for. Set a reminder on your phone or watch so you don’t forget. And even if you do miss an hour here and there, you can just fill in the gaps later.

There was a concern that the LEGO blocks wouldn’t do well in the sun and heat. But ours survived an entire day outside. So if you are worried, rest assured that the LEGO blocks will be okay. We live in Arizona and today it was 114°C outside.

LEGO Sundial Outdoor 12PM

My kids thought it was amazing that we could use the sun to tell time. The LEGO sundial also demonstrated how the shadow started out long in the morning and got much shorter by noon. Then it got longer again by late afternoon! 

Another observation was that the shadow moved in a clockwise direction. That’s why the modern clocks have the numbers set in the right rotation! Eureka!

LEGO Sundial Outdoor 430PM

Building the LEGO sundial was easy, but there was so much we learned from the sundial activity. I hope you and your kids enjoyed this activity as much as we did!

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