The Solar System: Vocabulary and Science in English

Introduction

The solar system is one of the most fascinating topics in science — and a rich source of English vocabulary. This guide covers the planets, key astronomical terms, and the language used to describe space and celestial phenomena.

The Eight Planets

In order from the Sun:

Planet	Key Facts	Type
Mercury	Closest to the Sun, no atmosphere, extreme temperatures	Terrestrial
Venus	Hottest planet, thick CO₂ atmosphere, rotates backward	Terrestrial
Earth	Only known planet with life, one moon	Terrestrial
Mars	Red planet, thin atmosphere, two moons (Phobos, Deimos)	Terrestrial
Jupiter	Largest planet, Great Red Spot storm, 95 known moons	Gas giant
Saturn	Famous rings made of ice and rock, 146 known moons	Gas giant
Uranus	Rotates on its side, ice giant, faint rings	Ice giant
Neptune	Farthest planet, strongest winds in solar system	Ice giant

Memory trick for planet order: “My Very Educated Mother Just Served Us Nachos” (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)

The Sun

The Sun is a star — a massive ball of hot plasma held together by gravity. Key facts:

Type: G-type main-sequence star (yellow dwarf)
Age: ~4.6 billion years
Diameter: ~1.4 million km (109 times Earth’s diameter)
Distance from Earth: ~150 million km (1 AU — Astronomical Unit)
Surface temperature: ~5,500°C
Core temperature: ~15 million°C

The Sun produces energy through nuclear fusion — hydrogen atoms fuse to form helium, releasing enormous energy.

Key Astronomical Vocabulary

Celestial Bodies

Term	Definition
star	a massive ball of plasma that produces light and heat through nuclear fusion
planet	a large body orbiting a star, with enough gravity to be roughly spherical
moon / satellite	a natural body orbiting a planet
asteroid	a rocky body smaller than a planet, mostly in the asteroid belt
comet	an icy body that develops a tail when near the Sun
meteor	a piece of rock burning up in Earth’s atmosphere (“shooting star”)
meteorite	a meteor that reaches Earth’s surface
dwarf planet	a body like Pluto — large enough to be spherical but hasn’t cleared its orbit
nebula	a cloud of gas and dust in space
galaxy	a system of billions of stars, gas, and dust

Orbital Mechanics

Term	Definition
orbit	the path of one body around another
revolution	one complete orbit around the Sun
rotation	spinning on an axis
axis	an imaginary line through a planet’s center
gravity	the force that attracts objects toward each other
gravitational pull	the attractive force of gravity
elliptical	oval-shaped (most orbits are elliptical, not circular)
perihelion	the point in an orbit closest to the Sun
aphelion	the point in an orbit farthest from the Sun

Light and Distance

Term	Definition
light-year	the distance light travels in one year (~9.46 trillion km)
astronomical unit (AU)	the average distance from Earth to the Sun (~150 million km)
light-second	the distance light travels in one second (~300,000 km)
parsec	~3.26 light-years (used by astronomers)

The Solar System’s Structure

Sun (center)
├── Inner Solar System (terrestrial planets)
│   ├── Mercury (0.39 AU)
│   ├── Venus (0.72 AU)
│   ├── Earth (1.00 AU)
│   └── Mars (1.52 AU)
├── Asteroid Belt (2.2–3.2 AU)
├── Outer Solar System (gas/ice giants)
│   ├── Jupiter (5.2 AU)
│   ├── Saturn (9.5 AU)
│   ├── Uranus (19.2 AU)
│   └── Neptune (30.1 AU)
├── Kuiper Belt (30–50 AU) — Pluto, Eris, other dwarf planets
└── Oort Cloud (2,000–100,000 AU) — source of long-period comets

Earth and Moon

Earth’s Key Features

Atmosphere: 78% nitrogen, 21% oxygen, 1% other gases
Hydrosphere: ~71% of surface covered by water
Tectonic plates: Earth’s crust is divided into moving plates
Magnetic field: protects from solar wind
Seasons: caused by Earth’s 23.5° axial tilt

The Moon

Only natural satellite of Earth
Distance: ~384,400 km
Diameter: ~3,474 km (about 1/4 of Earth’s)
Phases: new moon → crescent → quarter → gibbous → full moon
Tidal locking: the Moon always shows the same face to Earth
Tides: the Moon’s gravity causes Earth’s ocean tides

Space Phenomena

Phenomenon	Description
solar eclipse	Moon passes between Earth and Sun, blocking sunlight
lunar eclipse	Earth’s shadow falls on the Moon
aurora (borealis/australis)	colorful lights caused by solar particles hitting atmosphere
solar flare	a burst of radiation from the Sun’s surface
solar wind	a stream of charged particles from the Sun
black hole	a region where gravity is so strong nothing can escape
supernova	a massive stellar explosion
red giant	a star that has expanded as it ages
white dwarf	the remnant of a star after it sheds its outer layers

Useful Phrases for Discussing Space

"The Earth orbits the Sun once every 365.25 days."
"Jupiter is approximately 5.2 astronomical units from the Sun."
"The Moon's gravitational pull causes ocean tides."
"Scientists believe Mars may have had liquid water in the past."
"The Milky Way galaxy contains an estimated 100-400 billion stars."
"Light from the Sun takes about 8 minutes to reach Earth."
"The universe is approximately 13.8 billion years old."

Space Exploration Vocabulary

Term	Definition
spacecraft	a vehicle designed for travel in space
rocket	a vehicle propelled by burning fuel
satellite	an object placed in orbit around Earth
space station	a habitable structure in orbit
astronaut	a person trained for spaceflight (US/general)
cosmonaut	a Russian astronaut
rover	a vehicle that moves across a planet’s surface
probe	an unmanned spacecraft sent to explore
launch	to send a rocket into space
orbit	to travel around a celestial body
reentry	returning to Earth’s atmosphere
splashdown	landing in the ocean