Space

Asteroid | see definition»
one of thousands of rocky objects that move in orbits mostly between those of Mars and Jupiter and have diameters from a fraction of a mile to nearly 500 miles (800 kilometers)

Black hole | see definition»
a heavenly body with such strong gravity that light cannot escape it and that is thought to be caused by the collapse of a massive star

Comet | see definition»
A small bright heavenly body that develops a cloudy tail as it moves in an orbit around the sun.

Dwarf planet | see definition»
A heavenly body similar to a planet but too small to clear other objects from its orbit

Dwarf Planets in our solar system:
Ceres: a dwarf planet that orbits within the asteroid belt with a mean distance from the sun of 2.7 astronomical units (260 million miles) and a diameter of 590 miles (950 kilometers)

Eris: a dwarf planet with a mean distance from the sun of 67 astronomical units (6.2 billion miles) and a diameter of 1500 miles (2400 kilometers)

Haumea: a dwarf planet that orbits within the Kuiper belt with a mean distance from the sun of 43 astronomical units (6.45 billion kilometers) and a diameter of approximately 890 miles (1,430 kilometers)

Makemake: a dwarf planet that orbits within the Kuiper belt with a mean distance from the sun of 46 astronomical units (6.85 billion kilometers) and a diameter of approximately 930 miles (1,500 kilometers)

Pluto: a celestial object that orbits the sun at an average distance of 3.7 million miles (5.9 million kilometers) and has a diameter of about 1500 miles (2300 kilometers) and is often considered one of the planets

Galaxy| see definition»
Any one of the very large groups of stars that make up the universe

Light-year| see definition»
A unit of length in astronomy equal to the distance that light travels in one year or about 5.88 trillion miles (9.46 trillion kilometers)

Meteor| see definition»
One of the small pieces of matter in the solar system that enter the earth's atmosphere where friction may cause them to glow and form a streak of light

Milky Way | see definition»
a broad band of light that stretches across the sky and is caused by the light of a very great number of faint stars

Moon| see definition»
Smaller body that revolves around a planet

Planet | see definition»
Any large heavenly body that orbits a star (as the sun)

Planets in our solar system:
Mercury: the planet that is nearest the sun and has a diameter of about 3000 miles (4700 kilometers)

Venus: the planet that is second in order of distance from the sun and has a diameter of about 7,500 miles (12,100 kilometers)

Earth: the planet that is thirds in distance from the sun. The planet that we live on.

Mars: the planet that is fourth in order of distance from the sun, is known for its redness, and has a diameter of about 4200 miles (6800 kilometers)

Jupiter: the planet that is fifth in order of distance from the sun and is the largest of the planets with a diameter of about 89,000 miles (140,000 kilometers)

Saturn: the planet that is sixth in distance from the sun and has a diameter of about 75,000 miles (120,000 kilometers)

Uranus: the planet that is seventh in order of distance from the sun and has a diameter of about 32,000 miles (51,000 kilometers)

Neptune: the planet that is eighth in order of distance from the sun and has a diameter of about 31,000 miles (50,000 kilometers)

Solar system| see definition»
The sun and the planets, asteroids, comets, and meteors that revolve around it

Star| see definition»
Any of the heavenly bodies except planets which are visible at night and look like fixed points of light

Sun| see definition»
The heavenly body in our solar system whose light makes our day and around which the planets revolve