KnowSoda
ScienceEarth & Space
Solar System: fun facts and quiz
The essentials in 10 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
The Sun
The Sun is a star: a huge ball of hot plasma held together by its own gravity. It holds about 99.8% of all the mass in the Solar System.
Key fact
Sunlight is about 8 minutes old when it reaches you.
The Eight Planets
Eight planets orbit the Sun. In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Key fact
My Very Easy Method Just Speeds Up Naming them.
Rocky vs Giant Planets
The four inner planets are small and rocky. The four outer ones are giants: Jupiter and Saturn are gas giants, Uranus and Neptune are ice giants.
Key fact
You could not stand on Jupiter: it has no solid surface.
Our Moon
The Moon is Earth’s only natural satellite, about a quarter of Earth’s width. It shines by reflecting sunlight and always shows us the same face.
Key fact
The Moon has almost no air, so its sky is black even by day.
Days & Years
A planet’s day is one spin on its axis; its year is one trip around the Sun. Earth spins in about 24 hours and orbits in about 365 days.
Key fact
Venus takes longer to spin once than to orbit the Sun.
Orbits & Gravity
Planets orbit because the Sun’s gravity keeps pulling them inward while they move sideways. Their paths are ellipses, slightly stretched circles.
Key fact
Earth races around the Sun at about 30 km every second.
Distances in Space
Astronomers measure the Solar System in astronomical units (AU): Earth’s average distance from the Sun, about 150 million km.
Key fact
1 AU is about 150 million kilometres.
Seasons
Seasons happen because Earth’s axis is tilted about 23.4°. As Earth orbits, each hemisphere takes turns leaning towards the Sun.
Key fact
Earth is closest to the Sun in early January.
Moon Phases
The Moon is always half lit by the Sun. As it orbits Earth, we see different amounts of that lit half: the phases, from new to full.
Key fact
A full cycle of phases takes about 29.5 days.
Eclipses
In a solar eclipse the Moon passes between Earth and the Sun. In a lunar eclipse, Earth’s shadow falls on the Moon and can turn it coppery red.
Key fact
The Sun is about 400× wider than the Moon, and 400× farther.
Fun facts
About 1.3 million Earths could fit inside the Sun.
On average, all the other planets could fit side by side in the gap between Earth and the Moon.
Saturn is less dense than water. In a big enough bathtub, it would float.
The Moon is slowly drifting away from Earth, by about 3.8 cm every year.
Venus spins backwards compared with most planets, so there the Sun rises in the west.
Mercury’s orbit shifts slightly in a way Newton’s laws couldn’t explain. Einstein’s relativity could.
Sunlight takes about four hours to reach Neptune.
Uranus is tilted on its side, so each pole gets about 42 years of sunlight, then 42 years of darkness.
The Moon always shows us the same face, but it wobbles, so over time we can see about 59% of its surface.
As the Moon drifts away, total solar eclipses won’t last forever: in hundreds of millions of years it will look too small.
Story: The Planet Found with a Pen
The Planet Found with a Pen
1840s. Uranus keeps drifting off its predicted path, as if something unseen were tugging on it.
French mathematician Urbain Le Verrier works out where a hidden planet should be, and sends his prediction to Berlin.
On 23 September 1846, astronomers there point their telescope at that spot and find Neptune within an hour.
True or false?
Tap your answer to see if you got it, and why.
-
Question 1 of 10
The Sun is a star.
Show the answer
True. It is an ordinary star, the closest one to us.
-
Question 2 of 10
Mars is the fourth planet from the Sun.
Show the answer
True. Mercury, Venus, Earth, then Mars.
-
Question 3 of 10
Saturn is a rocky planet.
Show the answer
False. Saturn is a gas giant, made mostly of hydrogen and helium.
-
Question 4 of 10
The Moon makes its own light.
Show the answer
False. It only reflects sunlight.
-
Question 5 of 10
A year is the time a planet takes to spin once on its axis.
Show the answer
False. That is a day. A year is one full orbit of the Sun.
-
Question 6 of 10
Planets closer to the Sun travel faster in their orbits.
Show the answer
True. The Sun’s pull is stronger close in, so inner planets move faster.
-
Question 7 of 10
An astronomical unit is the distance from Earth to the Moon.
Show the answer
False. It is the Earth–Sun distance, about 390 times farther than the Moon.
-
Question 8 of 10
Seasons happen because Earth moves closer to and farther from the Sun.
Show the answer
False. The tilt of Earth’s axis causes seasons, not distance.
-
Question 9 of 10
Moon phases are caused by Earth’s shadow on the Moon.
Show the answer
False. Phases come from our changing view of the Moon’s sunlit half. Earth’s shadow only causes eclipses.
-
Question 10 of 10
A solar eclipse can only happen at new moon.
Show the answer
True. Only then does the Moon pass between Earth and the Sun.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. Solar System has 10 more ideas at the Advanced and Expert levels.
