Thursday, January 17, 2013
Exploration and Observation: North-South and Local Noon (Sundials, Part 2)
It's time for part 2 of our sundials activity from astronomer and physicist Laura Cotts! For this activity, you'll just need a piece of cardboard (I used the top of a pizza box) with a golf tee attached to the center, flat side down. In sundial terms, the golf tee is called a gnomon.
Find a sunny spot for your experiment and anchor it firmly. Draw the shadow of your gnomon every 15 minutes from 10:30 to 1:30. Record the time for each shadow. Find your very shortest shadow. It should point to the North because when the sun is at the highest point in its path, the sun is in the South.
The time of your shortest shadow is called “local noon”, when the sun is highest in the sky at your location. But this time may or may not match 12 noon on your clock! This is because the world is divided into “time zones” to make it easier for people to communicate. For instance, everyone in the Mountain Time Zone has clocks that say 12 noon at the same time, but the sun will cross its highest spot sooner for people in the eastern part of the time zone and later for people in the western part. (You can tell from the photo above that I'm in the western part of my time zone.)
Ever since there have been people, they have used the sun to help them find their way and to help them mark the passage of time. See what else you can learn!
What time was local noon for you? Was it before or after 12:00? Based on your local noon, do you think you live on the east or west side of your time zone? Check your answer here for a US time zone map or here for a world time zone map!