The Planets in Order (and a Paper Model That Shows How Far Apart They Are)

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Eight planets, in order from the Sun. Here's an easy way to remember them, one fact about each worth keeping, and a paper model that shows what posters never manage to: just how empty the Solar System is.

A mnemonic that sticks

My Very Educated Mother Just Served Us Nachos.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. (Older versions ended with "Nine Pizzas" for Pluto. In 2006 the International Astronomical Union reclassified Pluto as a dwarf planet, so the nachos stayed and the pizzas went.)

One fact for each

1. Mercury: the smallest planet and the closest to the Sun. A year there lasts just 88 Earth days.
2. Venus: the hottest planet, even though it's further from the Sun than Mercury. Its thick carbon-dioxide atmosphere traps heat, with surface temperatures around 465 °C.
3. Earth: the only planet we know of with liquid water oceans on its surface, and with life.
4. Mars: red because of iron oxide (rust) in its dust. It's home to Olympus Mons, the tallest volcano known in the Solar System.
5. Jupiter: the largest planet. All the other planets combined would still weigh less than Jupiter alone. Its Great Red Spot is a storm bigger than Earth.
6. Saturn: famous for its rings, mostly made of ice. Its density is so low that it would float in a (very large) bathtub.
7. Uranus: tipped over on its side, so it rolls around the Sun rather than spinning upright.
8. Neptune: the windiest planet, with the fastest winds measured in the Solar System. It was found by mathematics before anyone saw it through a telescope.

Five of them (Mercury, Venus, Mars, Jupiter, and Saturn) are bright enough to see with the naked eye.

The problem with posters

Almost every Solar System picture lines the planets up neatly, close together. That makes sense on a poster but gives the wrong impression. The real gaps are enormous, and they get bigger the further out you go.

Astronomers measure these distances in astronomical units (AU): 1 AU is the average distance from Earth to the Sun, about 150 million km.

Planet	Average distance from the Sun
Mercury	0.39 AU
Venus	0.72 AU
Earth	1.00 AU
Mars	1.52 AU
Jupiter	5.2 AU
Saturn	9.5 AU
Uranus	19.2 AU
Neptune	30.1 AU

Make a paper-strip Solar System

You need a strip of paper about 32 cm long (tape two strips together if needed), a ruler, and coloured pens or stickers.

Use the scale 1 AU = 1 cm:

1. Draw the Sun at the very left edge.
2. Mark Mercury at 4 mm, Venus at 7 mm, Earth at 1 cm, and Mars at 1.5 cm.
3. Mark Jupiter at 5.2 cm and Saturn at 9.5 cm.
4. Mark Uranus at 19.2 cm and Neptune at 30 cm.

Now look at it. The four rocky planets are crowded into the first 1.5 cm, and then there is a lot of nothing. That crowded little corner and the long empty strip are the real Solar System.

(For a bigger version, try one sheet of toilet roll per AU. You'll need about 30 sheets and a long hallway.)

The Solar System, in paper

Placing every planet yourself is one of the nicest ways to learn the order. In Paper Worlds, the Solar System scene in the Outer Space world asks you to arrange paper planets around a paper Sun, one at a time, until the whole family is there. The same world includes Orion and the Big Dipper and the zodiac, so you can build the sky you just learned.