Earth's Place in the Solar System

Earth is the third planet from the Sun and one of eight planets that orbit our star in a specific order.

Reading is good — doing is better. Practice Earth's Place in the Solar System as an interactive lesson.

Definition

Our solar system is made up of the Sun at the center, eight planets that travel around it in oval-shaped paths called orbits, along with moons, asteroids, and comets. Earth is the third planet from the Sun and the only known planet with liquid water, breathable air, and life.

Remember the rule

My Very Educated Mother Just Served Us Nachos — the first letter of each word stands for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, in order from the Sun.

Key words

Solar System: The Sun and everything that travels around it, including planets, moons, asteroids, and comets.
Orbit: The curved path an object takes as it travels around the Sun or another large body in space.
Planet: A large, round object in space that orbits the Sun and has cleared other objects out of its path.
Rotation: When Earth spins on its own axis, like a top — one full spin takes 24 hours and gives us day and night.
Revolution: Earth's full trip around the Sun — it takes about 365 days, which is one year.
Axis: An imaginary line through Earth from the North Pole to the South Pole that Earth spins around.
Astronomical Unit (AU): A unit of distance equal to the average distance from Earth to the Sun — about 93 million miles.
Inner and Outer Planets: The four planets closest to the Sun (Mercury, Venus, Earth, Mars) are inner planets; Jupiter, Saturn, Uranus, Neptune are outer planets.

Worked examples

Which planet is third from the Sun?

→ Earth is the third planet from the Sun, after Mercury (1st) and Venus (2nd). · Knowing the order helps you understand why Earth gets just the right amount of heat from the Sun.

How long does it take Earth to rotate once on its axis?

→ Earth completes one full rotation every 24 hours, which is one day. The side facing the Sun has daytime; the side facing away has nighttime. · Rotation causes day and night, not the seasons.

How long does it take Earth to revolve around the Sun?

→ Earth takes about 365 days (one year) to complete one full orbit around the Sun. · Every four years we add an extra day (February 29) called a leap day to make up for the leftover quarter-day each year.

How far is Earth from the Sun?

→ Earth is about 93 million miles (1 AU) from the Sun on average. · This distance puts Earth in the 'habitable zone' where liquid water can exist.

Name the planets in order from the Sun and identify which are inner planets.

→ Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mercury, Venus, Earth, and Mars are the four inner planets because they are closest to the Sun and are made mostly of rock.

Why does Earth have seasons?

→ Earth's axis is tilted at about 23.5 degrees. As Earth orbits the Sun, different parts of Earth receive more direct sunlight at different times of the year, creating spring, summer, fall, and winter. · Seasons are caused by Earth's tilt, NOT by how close Earth is to the Sun.

Common mistakes

Thinking seasons happen because Earth is closer to or farther from the Sun — seasons are actually caused by Earth's 23.5-degree tilt, not its distance from the Sun.
Confusing rotation and revolution — rotation is Earth spinning on its axis (1 day), revolution is Earth going around the Sun (1 year).
Believing the Sun moves across the sky — it only looks that way because Earth is rotating, not the Sun moving.
Saying there are nine planets — Pluto was reclassified as a dwarf planet in 2006, so there are eight official planets.
Thinking all planets take the same amount of time to orbit the Sun — planets farther from the Sun take much longer (Neptune takes 165 Earth years for one orbit).

FAQs

Why is Earth the only planet with life?

Earth is in the habitable zone — the right distance from the Sun for liquid water to exist. It also has a protective atmosphere with oxygen and a magnetic field that shields us from harmful solar radiation. No other planet in our solar system has all these conditions together.

What is the difference between a day and a year on Earth?

A day is the time it takes Earth to spin once on its axis — 24 hours. A year is the time it takes Earth to travel all the way around the Sun — about 365 days.

Does the Sun move?

The Sun looks like it moves across our sky from east to west, but that is actually caused by Earth rotating from west to east. The Sun does slowly orbit the center of the Milky Way galaxy, but we do not notice that motion day to day.

What holds Earth in its orbit?

Gravity! The Sun's gravity pulls on Earth and keeps it traveling in its oval-shaped orbit instead of flying off into space.

Why is Pluto no longer a planet?

Scientists decided a planet must orbit the Sun, be round, and have cleared other objects out of its orbital path. Pluto shares its orbit with many other icy objects in the Kuiper Belt, so it did not meet the third rule and was reclassified as a dwarf planet in 2006.

What is the difference between the inner and outer planets?

The four inner planets — Mercury, Venus, Earth, and Mars — are smaller, rocky, and closer to the Sun. The four outer planets — Jupiter, Saturn, Uranus, and Neptune — are much larger, made mostly of gas or ice, and much farther from the Sun.

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