My home-made globe. Apologies to anyone who lives on this planet for how badly it is drawn.
What you do:
If you don't have a globe, start by drawing a map of the world on the orange, so one end is the North Pole and the other is the South Pole. It doesn't have to be a work of art, just try to draw the continents in roughly the right spots.
Place the skewer through the orange. You may need an adult to help with this one.
Now if you spin the orange, it should look like the Earth spinning. You can use this as a globe.
Friday 21 June 2002, was that year's solstice. It is slightly different each year. You may have heard that this was the shortest day of the year, or the longest if you live in the northern hemisphere. When I first heard this, it confused me, because the day is always 24 hours long. What people are referring to when they are talking about the solstice is how long the sun is visible.
As the Earth orbits the Sun, its axis keeps pointing in the same direction.
You probably know that the Earth spins around once a day and that, every year, the Earth goes around the Sun in an almost circular orbit. If you imagine the Earth's orbit was a flat circle, then if the Earth's axis was straight up and down, the sun would always shine for the same amount of time each day: twelve hours. But the Earth is actually tilted over a bit, at 23.5 degrees to be exact. This week's activity looks at how this affects how much sunshine we receive each day.
Take your globe into the room and turn on the light. We are going to use the light to represent the Sun and the globe for the Earth.
Hold the globe at the same height as the light and with the axis straight up and down (North Pole at the top). If you are using a globe on a stand, you may need to tilt it over. Spin the globe and watch a couple of spots on the surface. You should find that each spot on the surface spends half its time in light and half its time in shadow. If the Earth's axis was not tilted, this is what would happen to us - the sun would shine for 12 hours each day.
Tilt the globe slightly so the North Pole points slightly towards the light. If you spin the globe now, you should see that points in the northern hemisphere spend more time in the light than in the dark, and the opposite is true for the southern hemisphere. Near the North Pole, there should even be areas that are constantly in the light, while near the South Pole, it is constantly in the shadow. This is what the Earth is like right now, with long summer days in the Northern hemisphere and short winter days in the South.
Keeping your globe tilted at the same angle and at the same distance from the light, move it around in a big circle to the other side of the light. The North Pole should now be pointing away from the light. If you spin the globe, you should find the opposite effect, points in the Southern Hemisphere spend more time in the light and the Northern Hemisphere less. This is what will happen to the Earth in six months, when there will be long summer days in the Southern Hemisphere and short winter days in the north.
Try moving the globe in a circle around the light with the axis tilted in the same direction. Compare how much light different spots receive at different points on the circle.
Right now, the Earth is tilted so the northern hemisphere has longer days
In six months, the Earth will be tilted the same way, but the Sun will be shining from the opposite direction, so the Southern Hemisphere will have longer days.
One day every year, the Earth is at a spot on its orbit of the Sun where the North Pole is pointed as close to the sun as it gets, so places in the Northern Hemisphere had the most hours of sunlight they will get all year, while places in the southern hemisphere received the least. In six months time, there will be another solstice, but this time Earth will be on the other side of the Sun, so the Southern Hemisphere will have more hours of sunlight and the northern hemisphere will have less.
The tilt of the Earth's axis is the reason we have seasons. This week, we have seen that it causes the length of the day to vary. This is one reason we have seasons, because the more hours the sun is shining on us, the more heat we receive from the sun and so, the warmer it is in our part of the world. But this is not the only factor that causes the seasons. The tilt of the axis also means that the intensity of the sunlight changes depending on the time of year. This will be the topic of another activity.
