Comprehensive Astronomy: Universe, Galaxies, Solar System, and Celestial Bodies

What is the universe?

Everything that exists — all matter, energy, space, and time.

What is a galaxy?

A huge system of billions of stars, planets, gas, and dust held together by gravity.

What is the Milky Way?

The galaxy that contains our solar system.

What is the solar system?

a group of planets, asteroids, comets and other celestial bodies that are in orbit around a star.

What is a star?

A massive ball of hot gas that produces energy by nuclear fusion.

What is a planet?

a celestial body that is in orbit around a star

What is an orbit?

The curved path an object follows around another due to gravity.

What is gravity?

The force of attraction between objects with mass.

What causes day and night?

Earth rotating on its axis once every 24 hours.

What causes the year?

Earth orbiting the Sun once every 365 days.

What causes the seasons?

The tilt of Earth's axis as it orbits the Sun.

What is the Moon?

Earth's natural satellite that orbits Earth.

What causes the phases of the Moon?

Different amounts of the Moon's sunlit side being visible from Earth.

What is an eclipse?

When one object in space blocks light from another.

What happens during a solar eclipse?

The Moon blocks sunlight from reaching Earth.

What happens during a lunar eclipse?

Earth blocks sunlight from reaching the Moon.

What is an asteroid?

A small rocky object that orbits the Sun

What is a comet?

A small icy object that orbits the Sun and forms a tail when heated.

What is the difference between a meteoroid, meteor, and meteorite?

Meteoroid: in space; Meteor: burning in atmosphere; Meteorite: reaches Earth.

What is the Big Bang Theory?

The theory that the universe began in a very hot, dense state and has been expanding ever since.

What is a celestial body

a naturally made object outside the Earth's atmosphere