Universe All matter and energy, including Earth, all the galaxies and space

Galaxy A collection of stars, gas, and dust that make up the universe. Diameter range: 1,500 to 300,000 light years

solar system The sun (a sun) combined with planets, moons, asteroids and comets, all traveling at high speed in orbits around the sun

star A giant sphere (ball) of gas that produces its own light by making its own energy through nuclear fusion. It’s held together by its own gravity. Life span: hundreds of millions or billions of years

sun A star that is orbited by planets and other bodies in a solar system Earth’s Sun: 93 million miles from Earth Diameter:864,000 miles (more than 100 times bigger than Earth) Supplies our planet Earth with light and heat

planet A celestial (relating to the sky or heavens) body that does not produce its own light, is larger than an asteroid and revolves around a sun which gives it light. Our Solar System: 8 planets

moon A natural satellite of a planet that orbits around a planet Jupiter has 28 moons Saturn has 30 moons Earth has 1 moon

eclipse The total or partial blocking of light from one celestial body as it passes through the shadow of another celestial body.

comet A celestial object that orbits the sun in an elliptical path.

asteroid Any small (often irregularly shaped bodies that orbit a sun. Diameter range: size of a speck of dust up to several hundred miles Many found in the region between the orbits of Mars and Jupiter

meteoroid A small rock floating in orbit near Earth (not in Earth’s atmosphere) When it enters atmosphere, it becomes a meteor and the friction with the air cause the rock to glow with heat

nebula A cloud of interstellar gas and dust Plural: nebulae or nebulas

black hole An extremely dense celestial object that nothing can escape, not even light. A black hole is formed by the collapse of a massive star’s core called a supernova

gravity is the attraction that objects have for each other because they have mass and occupy space. Because Earth is so huge it has a lot of gravity and it “pulls” us to the center of the Earth and keeps us attached to the surface.

Speed of light Light travels at a speed of 186,000 mi/sec. A traveler, moving at the speed of light, would circum-navigate the equator approximately 7.5 times in one second. By comparison, a traveler in a jet aircraft, moving at a ground speed of 500 mph, would cross the continental U.S. once in 4 hours.

Light year A light-year is a unit of distance. It is the distance that light can travel in one year. So in one year, light can travel about 10 trillion km. We use the term "light years" to describe the distance between stars, galaxies, and other objects that are humongous distances apart. For example, the closest star to the earth, not counting our own sun, is Alpha Centauri. This star, our closest stellar neighbor is 4.3 light years away from the earth! Think about that for a moment... The closest star to the earth (besides the sun) is 23,462,784,000,000 miles away from us!

rotation The motion of an object around its own axis The “spin” axis

revolution The motion of an object around another point, for example, around a sun, or the moon around the Earth.

orbit The path of a celestial body or an artificial satellite as it revolves around another celestial body

alien extraterrestrial being: a form of life assumed to exist outside the Earth or its atmosphere