What is this skill?
Our solar system is the sun and everything that travels around it. Eight planets orbit the sun, held in their paths by its gravity. The four inner planets are Mercury, Venus, Earth and Mars, and they are small and rocky. The four outer planets are Jupiter, Saturn, Uranus and Neptune, and they are giants. Earth takes about one year to orbit the sun once, and the moon orbits Earth. The sun itself is a star, the one closest to us.
In this practice a child puts the inner planets in order from the sun, then the outer planets, and later all six of the planets from Earth outward. Choice questions ask which planet we live on, what is at the center of our solar system (the sun), which planet is closest to the sun (Mercury), which is famous for bright rings (Saturn), which is the biggest (Jupiter) and which is called the Red Planet (Mars). Others ask what keeps the planets orbiting the sun (gravity), how long Earth takes to orbit the sun (about one year) and how many planets are in our solar system (eight). A sort asks whether a planet is rocky or a giant. The hardest questions ask why Mercury is very hot in the day and very cold at night (it has almost no atmosphere to hold heat), why the sun looks so much bigger than other stars (it is much closer to us), and whether a year on Jupiter is longer than a year on Earth (it is).
Why it matters
Space is one of the topics children love most, and it is a way to connect them to bigger science ideas: gravity, orbits, light and time. A child who is curious about Mars will happily learn about gravity and atmosphere to find out more.
The skill also pulls together the earlier lessons on day and night, seasons and forces. Earth spinning, Earth orbiting and gravity are the same ideas on a bigger scale.
Scale is the hard part, and it is good for the brain. The sun is a star that looks big only because it is near, and a year on another planet has a different length. Thinking about sizes and distances too large to picture is a stretch in the right direction.
Common mistakes
- Mixing up the order of the planets. A mnemonic sentence, one word per planet, helps: make up one together for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- Thinking a planet far from the sun must be hotter or colder in a simple way. Mercury is closest to the sun but swings from hot to cold because it has almost no atmosphere to hold heat.
- Believing the sun is the biggest or only star. It is a star like many others, and looks bigger because it is much closer.
- Thinking the moon is a planet or the sun orbits Earth. The moon orbits Earth, and Earth and the other planets orbit the sun.
How to help at home
- Make a scale model with a walk. Pick a spot for the sun and place a marker for each planet farther out, with the inner planets close together and the outer ones spread far apart.
- Invent a sentence to remember the order of the planets, and say it each time you see the moon or a bright planet at dusk.
- Use a flashlight and a ball to show how the moon appears to change shape as it orbits Earth. A dark room works best.
- Use a free sky map or telescope night at a local library or science center, if one is nearby, and try to spot a planet with your child.
Worked examples
These are real questions from the Tutorsaurus the solar system practice, with the answers worked out.
Example 1
Put the inner planets in order from the sun.
The pieces, mixed up: Earth / Mercury / Mars / Venus
Answer: Mercury Venus Earth Mars. From the sun: Mercury, Venus, Earth, Mars. These four are the rocky inner planets.
Example 2
Rocky planet or giant planet?
To sort: Mercury, Jupiter, Earth, Saturn, Mars, Neptune
Answer: Rocky planet: Mercury, Earth, Mars · Giant planet: Jupiter, Saturn, Neptune. Mercury, Earth and Mars are rocky inner planets. Jupiter, Saturn and Neptune are giant outer planets made mostly of gas and ice.
Example 3
A year on Jupiter is longer than a year on Earth.
Answer: True. True! Jupiter is much farther from the sun and takes almost 12 Earth years to orbit once.
Printable worksheet (PDF) — one page of questions from this practice that work on paper, easier ones first, with an answer key on page 2. Free to print, no sign-up.