Ages 6–8 · 8 little discoveries
Piko’s Space Models
Eight discoveries about the Sun, Earth and Moon model, Earth’s spin, day and night, orbits and years, the eight planets, rocky and giant planets, the Moon’s changing looks and the limits of a model that is not to scale.
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The Sun, Earth and Moon model
Say what goes around what in the Sun, Earth and Moon model: Earth goes around the Sun, and the Moon goes around Earth.
Piko draws a model of space. The Sun is in the middle. Earth is a planet, and it goes around the Sun along a path. The dotted ring is that path.
The Moon goes around Earth. In this picture Earth is in the middle, and the Moon travels on a small ring around it.
Careful: both of these pictures are wrong. The Sun does not go around Earth, and Earth does not go around the Moon. In real life the smaller body goes around the bigger one.
Now put it together. Earth goes around the Sun, and the Moon goes around Earth at the same time. Now you try: point to the Moon, then say what it goes around.
Earth spins on its axis
Show that Earth spins around its own axis, a line through the North and South Poles, and tell this spin from the trip around the Sun.
Earth is a big ball, and it spins. It turns around a line through its middle. The line is called the axis, and it runs from the North Pole to the South Pole. It is not a real stick; we only imagine it.
A toy top is a small model. It turns around a line through its middle and stays in one place. Earth spins the same way. One whole spin of Earth takes about a day, 24 hours.
Careful: spinning and going around are different. Something that spins stays in its place. Something that goes around makes a trip, like Earth around the Sun.
Now you try. This is Earth seen from above the North Pole. The golden dot marks one place, and Earth turns the way the little arrow points. Say where the dot goes next.
How day and night happen
Tell, from a picture, whether a marked place on Earth is in day or in night, and say that Earth’s spin carries the place from one to the other.
The Sun lights the half of Earth that faces it. Here the Sun is on the left, and the golden dot is our place. The dot is on the lit half, so it is day here.
The other half faces away from the Sun and is dark. Now the dot is on the dark half, so it is night here. The Sun has not gone out; it is lighting the other side.
Earth spins, so the dot is carried round. It moves from the lit half, across the edge, onto the dark half, where the Sun seems to go down. The Sun does not travel around Earth.
Careful: night does not come because the Sun goes away. It comes because our place turns away from the Sun. Now you try: find the golden dot. Is it on the lit half or the dark half?
Orbit: a trip takes a year
Say that Earth’s orbit is its path around the Sun, and that one whole trip along it takes one year.
The path a planet follows around the Sun is its orbit. Earth’s orbit is a ring, almost a circle. One whole trip around the Sun takes one year, about 365 days.
The flag shows where the year starts. Earth moves along the ring: a quarter of the way, half of the way, three quarters of the way. After a year it is back at the flag.
Careful: a day and a year are not the same trip. One spin of Earth on its axis takes about a day. One trip around the Sun takes about 365 days.
Now you try. Start at the flag and follow the four pictures. How many quarters of the trip make one whole year? Say it as you point.
The eight planets in order
Put the eight planets in order from the Sun, from Mercury to Neptune, and say that Pluto is a dwarf planet and not one of the eight.
Eight planets go around the Sun. In order from the Sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The picture puts them in a row. Earth is the third planet.
The four planets after Mars are Jupiter, Saturn, Uranus and Neptune. Neptune is the eighth planet and the farthest from the Sun.
Careful: Pluto is not one of the eight planets. Pluto is a dwarf planet. It is very small, even smaller than our Moon, and scientists do not count it among the eight.
Now you try. Say the planets in order. Then answer: which planet is fourth from the Sun? Which planet comes just after Jupiter?
Rocky planets and giant planets
Sort the eight planets into the four small rocky planets near the Sun and the four giant planets farther out.
Mercury, Venus, Earth and Mars are rocky planets. They are small, with hard ground, and they are the four planets closest to the Sun.
Jupiter, Saturn, Uranus and Neptune are giant planets, far from the Sun. Jupiter and Saturn are mostly gas. Uranus and Neptune are called ice giants. A giant has no hard ground to stand on.
Giants are huge. Here Jupiter and Earth are drawn to the same scale. Jupiter is about eleven times as wide as Earth, and more than a thousand Earths would fit inside it.
Careful: rings and heat do not decide the family. Saturn has rings, but it is a giant. Venus is very hot, but it is small and rocky. Now you try: ask how big it is and how far from the Sun.
The Moon’s changing looks
Say that the Sun always lights half of the Moon, and name four looks of the Moon, new moon, crescent, first quarter and full moon, by how much of the lit half we can see.
The Moon does not make its own light. The Sun lights it, like a lamp lighting a ball. The Sun always lights the half of the Moon that faces it. The other half is dark.
Over about four weeks the Moon seems to change. At new moon we cannot see it. Then a thin bright crescent appears. At first quarter half of the round shape is bright. At full moon all of it is bright.
Careful: the Moon does not change shape. It is always a ball. As the Moon goes around Earth, we see a different amount of its lit half. Earth’s shadow is not the reason.
Now you try. Look at how much of the round shape is bright: none, a thin curve, half or all. Say the name of the look.
When a model is not to scale
Say that a picture of the Sun, Earth and Moon is a model that is not to scale: it shows the order and who goes around whom, but not the real sizes and distances.
This model shows the Sun, Earth and Moon. It is a good model for who goes around whom. But it is not to scale: the sizes and the distances in it are not real.
Here the Sun and Earth have their real proportions. The Sun is about 109 times as wide as Earth, so Earth is only a tiny speck, the one the arrow points to.
Distances are not real in the first model either. If Earth were 1 centimetre wide, the Moon would be a small ball about 30 centimetres away, about the length of a ruler.
Careful: do not trust the sizes or the distances in a picture like this. Do trust the order and who goes around whom. Now you try: for the first model, say one thing you can trust and one you cannot.