Learn to find the time of the day without the help of a clock!
Sundials were used to tell the time of the day in olden times and is based on the principle that the position of the sun changes continuously during the day. In reality, it is the Earth that rotates around the sun making it seem like the sun rises in the east and sets in the west. As the sun moves across the sky, the central post on the sundial casts a shadow on its circular plate. It is just like reading a clock – the marks or calibrations on the plate tell you what time it is.
- Large paper or Styrofoam drinking cup with a plastic lid and straw
- Permanent marker
- Enough small pebbles to fill half of the cup
Estimated Experiment Time
15 minutes to set up the instrument and a day to get it working.
Making the Sundial:
What you will have now is a cup with a slanting straw passing through it – the major part of it forming an acute angle with the cup’s plastic lid.
- 1. Using the pencil, poke a hole on the side of the paper / Styrofoam cup approximately 2 inches below its top (rim).
- 2. Place the pebbles in the cup so to give it some weight and hold it upright.
- 3. Cover the cup with the plastic lid.
- 4. Put the straw through the hole on the side of the cup and its lid while letting about half an inch of the straw stick out from the side.
- 4. Secure the straw to the cup by taping it down on the side.
Setting up the Sundial:
In order to prepare the sundial you will need to rely on your wrist watch, so do keep it handy.
Begin in the morning on a sunny day when you will be home all day. Identify a spot out in the open that is sunny from 10 AM until 3 PM.
Next, use the compass to locate the North and let the long end of the straw point towards the North. Ensure that the position that you have chosen has no trees or buildings obstructing the Southern direction. Thereafter, place the sundial on level ground or else on a level table.
Once placed, be careful not to move the sundial. It is a good idea to make a mark the original position of the base of the cup on the ground or the table, so that it can be lined up again in case it moves accidentally.
Next, starting at 10 in the morning use the permanent marker to make marks on the lid of the cup where the shadow cast by the straw falls on it. Repeat this process every hour until 3 in the evening.
Remember, you can always continue with the marking process in case it becomes cloudy or if you have to leave.
Simple articles can be used to set up the ancient instrument that was used to tell the time of the day.
Using the wrist watch to calibrate (mark) your home-made sundial, you can use it to tell the time. All that needs to be kept in mind is that it is aligned properly with the straw on the cup’s lid pointing towards the North.
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