What is a hemisphere?

Half of the Earth. The equator cuts it into a northern half and a southern half, and the United Kingdom is in the northern one. You can halve it the other way too, along the prime meridian and the line opposite, which gives an eastern and a western hemisphere.

Why can I only see half the world?

Because that is what a ball looks like. Half of a globe faces you and the other half is round the back, so the picture stops at the edge, which is called the limb. The world map tool is the flat picture that shows all of it at once, at the cost of stretching the shapes.

Why does the globe not spin?

The lines are the point of it, and they only behave when the globe is centred on the equator with Greenwich in the middle: the lines of latitude are straight, the prime meridian is straight down the middle, and both poles are on the edge of the disc. Turned even a little, the equator bends into an arc and one of the poles disappears.

What are the tropics and the polar circles?

The Tropics of Cancer and Capricorn are at 23.5 degrees north and south, and they mark how far from the equator the Sun can ever be directly overhead. The Arctic and Antarctic Circles are at 66.5 degrees north and south, and inside them there are days in summer when the Sun does not set and days in winter when it does not rise.

Lines of the Globe

Geography · Year 3–Year 6

The equator, the tropics, the poles and the two halves, on a ball.

About the globe lines

A globe on the board, with the lines a class has to know on it. The first board is the five lines that run across it: the equator, the Tropics of Cancer and Capricorn, and the Arctic and Antarctic Circles. The second is the poles, the prime meridian and the two hemispheres. Tap any of them to name it, or work round the board with Next.

It is a ball rather than a flat map, and that is the whole reason for it. On a rectangle the northern hemisphere is the top half of a picture, which is true and says almost nothing; on a ball it is half the thing. The poles are two points rather than two long edges, and the prime meridian runs from one to the other instead of standing up a wall.

The coastlines are projected from public domain Natural Earth data, and only the half of the world facing you is drawn. That matters more than it sounds: a globe drawn without that clip puts Australia over the Atlantic and looks perfectly plausible.

The globe does not turn, and the reason is the lines. Centred on the equator at zero degrees, every line of latitude comes out as a straight line across the face of it, the prime meridian as a vertical one, and both poles land exactly on the top and bottom. Tilt it and the equator becomes an arc and one pole hides round the back.

The climate zones tool names three of these lines as well, over the bands they are the edges of, and that is the other half of the lesson: here they are lines on a sphere, there they are the boundaries of hot, mild and cold. The world map is where the rest of the world is.

How to use it on your whiteboard

1Tap a line, a pole or a half of the globe to name it.
2Tap Next to work round the board in order, and on into the second board.
3Tap Show all to put every label up at once, and Hide to ask the class again.
4Tap the board buttons to swap between the lines across and the poles and halves.

Questions

What is a hemisphere?: Half of the Earth. The equator cuts it into a northern half and a southern half, and the United Kingdom is in the northern one. You can halve it the other way too, along the prime meridian and the line opposite, which gives an eastern and a western hemisphere.
Why can I only see half the world?: Because that is what a ball looks like. Half of a globe faces you and the other half is round the back, so the picture stops at the edge, which is called the limb. The world map tool is the flat picture that shows all of it at once, at the cost of stretching the shapes.
Why does the globe not spin?: The lines are the point of it, and they only behave when the globe is centred on the equator with Greenwich in the middle: the lines of latitude are straight, the prime meridian is straight down the middle, and both poles are on the edge of the disc. Turned even a little, the equator bends into an arc and one of the poles disappears.
What are the tropics and the polar circles?: The Tropics of Cancer and Capricorn are at 23.5 degrees north and south, and they mark how far from the equator the Sun can ever be directly overhead. The Arctic and Antarctic Circles are at 66.5 degrees north and south, and inside them there are days in summer when the Sun does not set and days in winter when it does not rise.