The planets

The Planets (plus the Dwarf Planet Pluto)
Our solar system consists of the sun, eight planets, moons, dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The sun is the center of our solar system; the planets, their moons, the asteroids, comets, and other rocks and gas all orbit the sun.

The nine planets that orbit the sun are (in order from the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet or plutoid). A belt of asteroids (minor planets made of rock and metal) lies between Mars and Jupiter. These objects all orbit the sun in roughly circular orbits that lie in the same plane, the ecliptic (Pluto is an exception; it has an elliptical orbit tilted over 17° from the ecliptic).

Easy ways to remember the order of the planets (and Pluto) are the mnemonics: "My Very Excellent Mother Just Sent Us Nine Pizzas" and "My Very Easy Method Just Simplifies Us Naming Planets" The first letter of each of these words represents a planet - in the correct order.





The largest planet is Jupiter. It is followed by Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury, and finally, tiny Pluto (a dwarf planet). Jupiter is so big that all the other planets could fit inside it.

The Inner Planets vs. the Outer Planets
The inner planets (those planets that orbit close to the sun) are quite different from the outer planets (those planets that orbit far from the sun).
The inner planets are: Mercury, Venus, Earth, and Mars. They are relatively small, composed mostly of rock, and have few or no moons.
The outer planets include: Jupiter, Saturn, Uranus, Neptune, and Pluto (a dwarf planet). They are mostly huge, mostly gaseous, ringed, and have many moons (again, the exception is Pluto, the dwarf planet, which is small, rocky, and has one large moon plus two tiny ones).

Temperatures on the Planets
Generally, the farther from the Sun, the cooler the planet. Differences occur when the greenhouse effect warms a planet (like Venus) surrounded by a thick atmosphere.

Density of the Planets
The outer, gaseous planets are much less dense than the inner, rocky planets.

The Earth is the densest planet. Saturn is the least dense planet; it would float on water.

The Mass of the Planets
Jupiter is by far the most massive planet; Saturn trails it. Uranus, Neptune, Earth, Venus, Mars, and Pluto are orders of magnitude less massive.

Gravitational Forces on the Planets
The planet with the strongest gravitational attraction at its surface is Jupiter. Although Saturn, Uranus, and Neptune are also very massive planets, their gravitational forces are about the same as Earth. This is because the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of the planet's radius squared.

A Day on Each of the Planets
A day is the length of time that it takes a planet to rotate on its axis (360°). A day on Earth takes almost 24 hours.

The planet with the longest day is Venus; a day on Venus takes 243 Earth days. (A day on Venus is longer than its year; a year on Venus takes only 224.7 Earth days).

The planet with the shortest day is Jupiter; a day on Jupiter only takes 9.8 Earth hours! When you observe Jupiter from Earth, you can see some of its features change.

The Average Orbital Speed of the Planets
As the planets orbit the Sun, they travel at different speeds. Each planet speeds up when it is nearer the Sun and travels more slowly when it is far from the Sun (this is Kepler's Second Law of Planetary Motion).

The Planets in Our Solar System
Planet Distance from the Sun
(Astronomical Units
miles
km) Period of Revolution Around the Sun
(1 planetary year) Period of Rotation
(1 planetary day) Mass
(kg) Diameter
(miles
km) Apparent size
from Earth Temperature
(K
Range or Average) Number of Moons
Mercury 0.39 AU, 36 million miles
57.9 million km 87.96 Earth days 58.7 Earth days 3.3 x 1023 3,031 miles
4,878 km 5-13 arc seconds 100-700 K
mean=452 K 0
Venus 0.723 AU
67.2 million miles
108.2 million km 224.68 Earth days 243 Earth days 4.87 x 1024 7,521 miles
12,104 km 10-64 arc seconds 726 K 0
Earth 1 AU
93 million miles
149.6 million km 365.26 days 24 hours 5.98 x 1024 7,926 miles
12,756 km Not Applicable 260-310 K 1
Mars 1.524 AU
141.6 million miles
227.9 million km 686.98 Earth days 24.6 Earth hours
=1.026 Earth days 6.42 x 1023 4,222 miles
6,787 km 4-25 arc seconds 150-310 K 2
Jupiter 5.203 AU
483.6 million miles
778.3 million km 11.862 Earth years 9.84 Earth hours 1.90 x 1027 88,729 miles
142,796 km 31-48 arc seconds 120 K
(cloud tops) 18 named (plus many smaller ones)
Saturn 9.539 AU
886.7 million miles
1,427.0 million km 29.456 Earth years 10.2 Earth hours 5.69 x 1026 74,600 miles
120,660 km 15-21 arc seconds
excluding rings 88 K 18+
Uranus 19.18 AU
1,784.0 million miles
2,871.0 million km 84.07 Earth years 17.9 Earth hours 8.68 x 1025 32,600 miles
51,118 km 3-4 arc seconds 59 K 15
Neptune 30.06 AU
2,794.4 million miles
4,497.1 million km 164.81 Earth years 19.1 Earth hours 1.02 x 1026 30,200 miles
48,600 km 2.5 arc seconds 48 K 2
Pluto (a dwarf planet) 39.53 AU
3,674.5 million miles
5,913 million km 247.7 years 6.39 Earth days 1.29 x 1022 1,413 miles
2,274 km 0.04 arc seconds 37 K 1 large (plus 2 tiny)
Planet Distance from the Sun
(Astronomical Units
miles
km) Period of Revolution Around the Sun
(1 planetary year) Period of Rotation
(1 planetary day) Mass
(kg) Diameter
(miles
km) Apparent size
from Earth Temperature
(K
Range or Average) Number of Moons

Another Planet?
In 2005, a large object beyond Pluto was observed in the Kuiper belt.

A few astronomers think that there might be another planet or companion star orbiting the Sun far beyond the orbit of Pluto. This distant planet/companion star may or may not exist. The hypothesized origin of this hypothetical object is that a celestial object, perhaps a hard-to-detect cool, brown dwarf star (called Nemesis), was captured by the Sun's gravitational field. This planet is hypothesized to exist because of the unexplained clumping of some long-period comet's orbits. The orbits of these far-reaching comets seem to be affected by the gravitational pull of a distant, Sun-orbiting object.

Planet Activities and Quizzes
Planet Coloring pages

An interactive puzzle on the Solar System.

Find It!, a quiz on the planets.

A fill-in-the-blank (cloze) activity on the Solar System - or go to the answers.

Solar System Model to make.

Solar System calendar to print out and color.

Solar System Crafts

How to write a report on a planet - plus a rubric.



Astronomy: K-3 Theme Page
Activities, quizzes, books to print, and printouts.

Nine Planets
A Book With Tabs
An activity book on the Solar System to print for fluent readers. The book contains information, pictures, and questions to answer.

The Solar System Book
A simple printable coloring book about the Solar System to print (for early readers). Pages on the Solar System, the sun, Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Solar System Coloring Book


Color and learn about our Solar System, the Sun, the planets, asteroids, comets, and our moon.


Solar System Diagram
Label the Sun and planets.
Answers

Earth's Atmosphere
Label the atmospheric layers of the Earth.
Answers

Earth Diagram
Label the inside of the Earth.
Answers

Celsius Bar Graph Questions #2:
Printable Worksheet
A printable activity worksheet in which the student reads a bar graph of the average temperatures of the planets to answer questions, for example, "On average, is it warmer on Jupiter or Mars?" Or go to the answers. Go to a pdf version of the worksheet.


Moon Phases Diagram
Label the phases of the waxing and waning moon.
Answers

Lunar Eclipse Diagram
Label the lunar eclipse.
Answers

Planet-Sun Orbital Diagram
Label the aphelion (farthest point in orbit) and perihelion (closest point in orbit) of a planet in orbit.
Answers


Put 10 Planet Words in Alphabetical Order - Worksheet
Put 10 planet words in alphabetical order. The words are: Earth, Jupiter, Mars, Mercury, moon, Neptune, Pluto, Saturn, Uranus, Venus. Go to the answers.

The Planets in English
A Label Me! Printout
Label the Solar System in English.
Answers

The Planets in French
A Label Me! Printout
Label the Solar System in French.
Answers


The Planets in German
A Label Me! Printout
Label the Solar System in German.
Answers

The Planets in Italian
A Label Me! Printout
Label the Solar System in Italian.
Answers

The Planets in Portuguese
Label the planets in Portuguese.
Answers