The diagonal of your triangle is in line with the equator.
Starting at the point where the other line is touching the circle, draw a second line so it makes a right angle (it doesn’t matter whether it goes left or right). Make this new line the length you just calculated in Step 11.
Join the ends of these two lines to make a right-angled triangle.
Draw a line that cuts the circle in half. This line must run parallel to the long side of the triangle. This line represents the Earth’s equator.
Draw another line that cuts the circle into quarters. This line must be at right angles to the equator. This represents the line connecting the Earth’s poles.
Find where you wrote ‘me’. How close is your position to the equator? How close is your position to the South Pole?
What’s happening?
This activity measures the angle between the ground and the Sun. This angle changes throughout the day, with the Sun at the horizon at dawn and dusk, and high in the sky at noon. The measurement also changes throughout the year – in summer, the southern half of the world is tilted towards the Sun. In winter, the south pole is tilted away from the Sun. There are only two days a year where the Earth is not tilted with one end closer to the Sun. These two days are called the equinoxes, and they occur in September and March, when the seasons are changing.
On the equinox, the Sun is sitting directly above the equator, which makes calculating latitudes a lot easier. After the equinox, the Earth tilts, and the Sun no longer sits directly above the equator – in Summer, the Sun is directly above a point somewhere in the southern tropics. You can still calculate your latitude when it is not the equinox, but the calculation is more complicated.
Real-life maths
People have known that the Earth was round for thousands of years, and they have used this fact to calculate latitude. Using the Sun to calculate latitude is quite difficult, because the Sun moves around throughout the day and the year. However, the stars are a lot more predictable, and one star in particular is very useful. Polaris, the North Star, sits directly above the North Pole. If you can measure the angle to Polaris, you can work out your latitude. Unfortunately, you can only see Polaris if you are in the northern hemisphere.
Latitude only tells you how far north or south you are. In order to know exactly where you are on the Earth, you also need to know how far east or west you are. This measurement, called longitude, is just as important for navigating as latitude, but is much more difficult to measure. Captain Cook had an experimental clock on his second and third journeys that he used to calculate longitude.
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