The Sun-Earth-Moon System, Solar System, and Universe Vocabulary

Vocabulary flashcards covering key terms and definitions regarding the Sun-Earth-Moon system, planetary objects, star systems, galaxies, and the universe.

Revolution

The orbit of an object around another object, such as Earth orbiting the Sun once every $365.25\,\text{days}$.

Astronomical Unit (AU)

A unit of measurement equal to the average distance between Earth and the Sun, which is about $150\,\text{million}\,\text{km}$.

Rotation

The spin of an object around its own axis, which takes $24\,\text{hours}$ for Earth and causes day and night.

Equinox

One of two days during the year (at the beginning of spring and fall) when Earth's axis does not tilt toward or away from the Sun.

Solstice

One of two days during the year (at the beginning of summer and winter) when Earth's axis tilts the most toward or away from the Sun.

Waxing Moon

The phase period over two weeks following a new moon during which the visible lit portion of the Moon facing Earth grows.

Waning Moon

The phase period over two weeks following a full moon during which the visible lit portion of the Moon facing Earth shrinks.

Tides

The daily rising and falling levels of the oceans and other large bodies of water caused by the gravitational pull of the Moon and the Sun.

Eclipse

The movement of one solar system object into the shadow of another solar system object.

Solar Eclipse

An event during which people in the Moon's shadow on Earth see the Moon partially or completely cover the Sun.

Lunar Eclipse

An event during which people on Earth see Earth's shadow partially or completely cover the Moon.

Solar System

The Sun and everything that orbits it, formed from a cloud of gas and dust that pulled together due to gravity.

Planet

An object that orbits the Sun, is massive enough to be pulled by gravity into a nearly spherical shape, and has no other large object in its orbital path.

Dwarf Planet

An object that orbits the Sun and is nearly spherical in shape, but shares its orbital path with other objects of similar size.

Moon

A natural satellite that orbits an object other than a star.

Asteroids

Small, rocky objects that orbit the Sun, many of which are located in the asteroid belt between Mars and Jupiter.

Comets

Small, icy objects that orbit the Sun and develop tails as they get close to the Sun.

Meteoroids

Solid bits of debris that travel through the solar system.

Meteor

A streak of light produced when a meteoroid passes through Earth's atmosphere.

Meteorite

A meteoroid that reaches Earth.

Inner Planets

The $4$ rocky planets closest to the Sun (Mercury, Venus, Earth, Mars) made of solid elements with few or no moons, which rotate more slowly than outer planets.

Outer Planets

The $4$ gas planets (Jupiter, Saturn, Uranus, Neptune) made mainly of gas and low-boiling materials, featuring large sizes, thick atmospheres, weather systems, and many moons.

Star

A large sphere of hydrogen gas that is hot enough for nuclear reactions to occur in its core.

Light-Year

A unit of measurement equal to the distance light travels in one year, which is $9.46\,\text{trillion}\,\text{km}$.

Binary Star System

A star system in which $2$ stars orbit each other's center of gravity.

Galaxy

A huge collection of stars, gas, and dust pulled together by gravity.

Elliptical Galaxies

Galaxies shaped like basketballs or footballs that contain mainly older, redder stars and very little dust or gas.

Irregular Galaxies

Oddly shaped galaxies containing large amounts of gas and dust where many new stars form.

Spiral Galaxies

Galaxies with a central bulge containing older redder stars and bluish, curved, dust-filled arms containing younger stars.

Milky Way

A large spiral galaxy containing more than $100\,\text{billion}$ stars, in which our Sun is located in one of the arms about halfway from the center.

Local Group

The cluster of galaxies that includes the Milky Way.

Big Bang Theory

The theory that the universe began from a single hot, dense point between $13$ and $14\,\text{billion}$ years ago and has been expanding and cooling ever since.