Advertisement Upgrade to remove ads


the apparent shift in an objects position when viewed from two locations


all of space and everything in it


The distance that light travels in one year

Scientific Notation

Uses powers of 10 to write very large numbers or very small numbers in a shorter form.


A giant ball of gas primarily hydrogen and helium


An object that orbits a star, is large enough to have become rounded by its own gravity and has cleared the area of its orbit.

Solar System

the system composed of the sun (a star) and the planets and other bodies that travel around the sun

Binary Star

a star system with two stars


large group of stars, dust, and gas held together by gravity; can be elliptical, spiral, or irregular

Spiral Galaxy

A galaxy with a bulge in the middle and arms that spiral outward in a pinwheel pattern.

Elliptical Galaxy

a galaxy shaped like a round or flattened ball, generally containing only old stars

Irregular Galaxy

a galaxy that does not have a regular shape


an enormously bright, distant galaxy with a giant black hole at its center


the path of an object as it revolves around another object in space


a push or pull exerted on an object

Law of Universal Gravitation

the scientific law that states that every object in the universe attracts every other object


a measure of the amount of matter in an object


The measure of the force of gravity on an object.


the tendency of an object to resist a change in motion.

Newtons first law of motion

an object in motion will remain in motion unless acted upon by another force


The process of building something up gradually by the gathering together of smaller pieces.


an instrument that separates light into colors and makes an image of the resulting spectrum.

Apparent Brightness

the brightness of a star as seen from earth

Absolute Brightness

the brightness a star would have if it were at a standard distance from earth

Hertzsprung-russell diagram

a graph relating the surface temperatures and absolute brightness of stars

Main Sequence

a diagonal area on an H-R diagram that includes more than 90 percent of all stars


a large cloud of gas and dust in space, spread out in an immense volume.

Proto star

A contracting cloud of gas and dust with enough mass to form a star.

White Dwarf

the blue-white hot core of a star that is left behind after its outer layers have expanded and drifted out into space.

Super Nova

The brilliant explosion of a dying supergiant star.

Neutron Star

the small, dense remains of a high-mass star after a supernova.


a rapidly spinning neutron star that produces radio waves

Black hole

an object whose gravity is so strong that nothing, not even light, can escape.


The central region of the sun, where nuclear fusion takes place.

Nuclear Fusion

the process in which two atomic nuclei combine to form a larger nucleus, forming a heavier element and releasing huge amounts of energy.

Radiation Zone

a region of very tightly packed gas where energy is transferred mainly in the form of electromagnetic radiation.

Convection Zone

the outermost layer of the sun's interior.


The inner layer of the sun's atmosphere that gives off its visible light.


the middle layer of the sun's atmosphere.


Outer layer of the sun's atmosphere.

Solar Wind

A stream of electrically charged particles produced by the sun's corona.


A loop of gas that protrudes from the sun's surface, linking parts of sunspot regions.

Solar Flare

An eruption of gas from the sun's surface that occurs when the loops in sunspot regions suddenly connect.


violent and excited activity.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again


Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording