Lesson 3 Page 3
Discover: Using the Sun to Tell Time
Before clocks were invented, people used water, sand, candles, and even shadows to tell time.
Try This
You might have noticed that the length and location of your shadow changes throughout the day. Go outside early in the morning on a sunny day and mark an “x” on the ground. Place a tall object on the “x” – such as a vase or paper towel roll. Trace its shadow on the ground. Go outside again at noon and trace the shadow as it appears at that time. Then, go one more time in the afternoon and trace the shadow a third time. You will see how the shadows have changed.
Depending on where you are located and the time of year, the location of the Sun and the shadows it produces will vary.
In summer or closer to midday, the Sun seems higher in the sky and it casts shorter shadows than in morning or afternoon.
In the winter or closer to morning or evening, the Sun is lower in the sky and casts longer shadows.
Video
In this activity, you will build your own simple sundial.
Because the time depends on where you are on the planet, you need to use a compass to orient yourself in this activity. A compass needle (which is attracted to the magnetic field of the earth) points in a direction called magnetic north. It is not exactly the same as geographic north (the North Pole), but for the purposes of this activity, it is close enough.
The Sundial in this activity uses geographic north as a reference point. If you do not line up the diagram printout with geographic north, the Sundial will not give you the correct time.
If you live in the middle of your time zone, your Sundialwill be quite accurate. If you are at one edge of your time zone, the time on your Sundial (solar time) may differ from the time on your watch (standard time) by as much as forty minutes. That
means, if you live in Lloydminster or Medicine Hat, your Sundial will be very different from that of someone in Grande Prairie. It should be reasonably accurate for Edmonton and Calgary. (You could find a time zone map in an atlas or on the Internet
to determine where in your time zone you live.)
Historical Connection
Why do we use standard time rather than sun dials? We have Canadian engineer, Sir Sanford Flemming to thank.He invented time zones with one hour time difference between regions.
Technology Connection
Have you ever watched your local news when the newscaster told the time the Sun will rise and set that day? How do they know this?
The rise and set of the Sun is on a predictable cycle in relation to Earth. You may google the sunrise and sunset times for your location at this website. If you download the free Sundroid app for an android phone, you can find what time the Sun will rise and set anywhere on any date!
- Scroll on the map of the world and locate where you live. (The map might show Europe! Place your cursor on it and move the map around to find your location.) Click the + or – sign in the upper left-hand corner of the map to see more or less detail. You should be able to find a town or city near you.
- Click that spot on the map (and a red pushpin will appear).
- Confirm that the correct name of the town or city appears next to the map (in the top right corner).
- On the bottom right-hand corner, click the “Change” Time Zone and select the correct time zone (MT for Alberta) from the list.
- Confirm that the times displayed are now for the correct time zone.
You can read the information given about your location!
Video |
Watch this ADLC Digital Lesson on making a Sundial.
Notebook: How can a sundial track the time of day?
- Click here to download this activity.
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Save to your Sky Science Notebook.