Stars and Planets
Stars and planets are both objects in space, but they are not the same kind of object. The most important difference is this:
- a star makes its own light
- a planet does not make its own light
Examples:
- the Sun is a star
- Earth is a planet
- Jupiter is a planet
What a star is
A star is a huge, extremely hot ball of gas.
Stars produce their own light and heat, which is why the Sun is so important to life on Earth.
Some stars are:
- bigger than the Sun
- smaller than the Sun
- red, white, blue, or yellowish
Even though stars can look tiny in the night sky, many of them are far larger than Earth.
What a planet is
A planet is a large, nearly round object that orbits a star.
Planets do not produce their own light. We usually see them because they reflect light from a star.
Planets can be:
- rocky
- icy
- covered by thick gas
Some planets are relatively small, and some are enormous.
How stars and planets are different
Stars and planets are different in a few big ways:
- stars glow with their own light
- planets reflect light
- stars are much hotter than planets
- planets travel around stars
A star is a light source. A planet is an object lit by that source.
Different kinds of planets
In our solar system, planets are not all alike.
- Mercury, Venus, Earth, and Mars are rocky planets
- Jupiter and Saturn are giant planets with lots of gas
- Uranus and Neptune are often called ice giants
So the word "planet" includes several different kinds of worlds.
Different kinds of stars
Stars are not all alike either.
They can be different in:
- size
- color
- temperature
- brightness
Some stars are cooler and look redder. Some are hotter and look whiter or bluer.
Solar systems and galaxies
A solar system is a star and the objects that orbit it.
That can include:
- planets
- moons
- asteroids
- comets
Our solar system is built around the Sun.
A galaxy is a huge collection of stars, gas, dust, and planetary systems held together by gravity.
Our solar system is part of the Milky Way galaxy.
What we see in the night sky
Many of the points of light you see in the night sky are stars.
Some of the brighter objects that slowly shift position over time are planets.
People also group stars into patterns called constellations. These patterns are useful for identifying regions of the sky, even though the stars in a constellation are often very far apart in space.
Final takeaway
At the most basic level:
- stars and planets are not the same
- stars make their own light
- planets travel around stars
- planets can be rocky, icy, or gas-rich
- solar systems belong inside galaxies