Try this: Sundial

You will need

• Ruler
• Craft knife
• Thin cardboard
• Glue
• A sundial template from our web site
  • If you live in an Australian state capital or Townsville
  • If you live somewhere else in the Southern Hemisphere
  • If you live in the Northern Hemisphere
• A compass
• Sticky tape (optional)
• A toothpick
• An adult

• A protractor
• Your latitude (the angle between where you live and the equator). In Australia, you can find your latitude through Geoscience Australia

Warning: have an adult help you use the knife.

What to do

You need to set up your sundial so it is leaning over. How far over it leans depends on your latitude.

1. Print out the templates and stick them to cardboard.
• If you can, try printing them directly onto the cardboard with a printer or photocopier.
2. Cut out the parts marked Dial, Dial Holder and Crossbar from the template.
3. On each of the Dial Holders, there is a corner with several lines coming from it. Draw a line from this corner, so the angle between your line and the side of the Dial Holder is the same as your latitude. (If you live in an Australian capital or Townsville, your line is already marked.)
4. With the help of an adult, cut along your line, between the two curved lines.
5. Cut along the lines marked "Cut here" on the Dial holders and Crossbar.
6. Put the tabs of the Dial into the slots you have cut in the Dial Holders.
7. Attach the crossbar to the back of the Dial Holders.
8. Stick a toothpick through the centre of the sundial. (You may need to use a piece of blu-tak or plasticine to make sure it sticks straight up.)
9. Set up your sundial somewhere the Sun is shining, with the top of the Sundial facing north (south if you live in the northern hemisphere).
10. The shadow of the toothpick will show you the time. In winter months, you may find the Sun is too low to shine on the numbered side of the sundial, but you can still tell time by using the sunlight and shadow shining through the cardboard.

What's happening?

You have made a simple equatorial sundial.

A basic sundial consists of two parts: one that casts the shadow, called a gnomon; and something for the shadow to be cast on to, called the dial plate. As the Earth spins, the shadow of the gnomon moves against the dial plate, which is marked to show the time.

Your sundial is tilted so the gnomon (toothpick) is parallel to the Earth's axis (the line the Earth spins around) and the dial plate is parallel to the equator. In 24 hours the Earth spins 360 degrees relative to the Sun, so it spins 15 degrees per hour. On your sundial, the hour marking are 15 degrees apart, so the shadow takes around one hour to more from one marking to the next.

You may find your sundial does not agree with your watch. There are two main reasons for this:

• The path the Sun appears to take as it moves across the sky changes over the course of a year. This is due to two effects. Firstly, the Earth's axis is tilted, so in summer the Sun appears to be higher in the sky than in winter. Secondly, the Earth isn't always the same distance from the Sun. The Earth's orbit is an ellipse, not a circle, so sometimes we are slightly closer to the Sun than other times. These two effects combine so the Sun isn't always in the same place in the sky at a particular time of day. Therefore any sundial can run fast or slow, depending on the time of year.
• Time zones: If one town is east or west of another, the times shown on a sundial in both towns will be different. For example, today a sundial in Canberra would have said it was 12:00 pm at the same time that a sundial in Melbourne, to the west, said it was 11:42 am. This is just because the Earth is spinning eastwards, so the further west you go, the later the Sun rises and sets. Many years ago, people would measure their local time using sundials and then set their clocks and other timepieces to match. As transport and communication became faster, this became confusing, so the world was divided into time zones. The time is considered to be the same everywhere inside a particular time zone, even if a sundial says the local time is faster or slower.

Applications

• Sundials were one of the earliest ways of measuring time and have been used for over 3500 years.
• By comparing the time measured on a sundial at two locations, you can work out how far east or west they are from each other. Before GPS and other high-tech devices became available, sailors and mapmakers would measure their longitude (how far east and west they were) by measuring the local time and comparing it to clocks set to match a known location, such as the Royal Observatory at Greenwich in the UK, where 0 degrees longitude is considered to be.