The Solar System
Earth does not exist in isolation. It is one of eight planets orbiting a star called the Sun. Together, this collection of objects is called the Solar System.
The Sun
The Sun is a star — a massive ball of hot plasma fusing hydrogen into helium and releasing enormous energy. It is about 109 times the diameter of Earth and accounts for 99.86% of the Solar System’s total mass.
For humans, the Sun is essential. It:
- Provides light and heat
- Powers photosynthesis (how plants make food)
- Drives weather patterns
- Has been worshipped as a god by many civilizations (Major World Religions)
The Sun rises in the east and sets in the west every day. This is how humans originally oriented themselves in space before compasses and GPS.
The Eight Planets
In order from the Sun:
| Planet | Notable Features |
|---|---|
| Mercury | Smallest, closest to Sun, extreme temperatures |
| Venus | Hottest (runaway greenhouse effect), covered in clouds |
| Earth | You are here. Only known inhabited planet. |
| Mars | Red, thin atmosphere, polar ice caps. Humans want to colonize it. |
| Jupiter | Largest planet. A gas giant with a massive storm (Great Red Spot). |
| Saturn | Famous for its beautiful ring system |
| Uranus | Rotates on its side, extremely cold |
| Neptune | Windiest planet, very far away |
Other Objects
- Moon — Earth’s natural satellite. It orbits Earth once every ~27 days. Humans have landed on it (1969). It causes ocean tides.
- Asteroids — rocky objects, mostly between Mars and Jupiter
- Comets — icy objects that form tails when near the Sun
- Dwarf planets — including Pluto (formerly a planet, demoted in 2006, which caused significant human controversy)
Why Does This Matter?
Humans track the Sun and Moon for:
- Calendars — months are based on the Moon; years on Earth’s orbit
- Agriculture — planting by seasons
- Navigation — sailors used stars to find their way
- Culture — many holidays align with solstices, equinoxes, and lunar cycles
Related: What is Earth | The Universe | What is Culture Next: The Universe