binary star
Member of a double star system
constellation
A group of stars that form a pattern in the sky
nebula
a large cloud of dust and gas that can break apart into smaller pieces and form stars
galaxy
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 spherical or elongated galaxy with a bright center and very little dust and gas; contain older stars
irregular galaxy
a galaxy that does not fit into any other category; one with an irregular shape
spectrum
colored band produced when a beam of light passes through a prism
big-bang theory
theory that the universe began to expand with the explosion of concentrated matter and energy and has been expanding ever since
quasar
a "quasi-stellar" object; a starlike source of light that is extremely far away; one of the most powerful sources of energy in the universe
cosmic background radiation
radiation left over from the beginning of the universe
open cluster
a star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars
globular cluster
circular shaped star cluster tightly bound with thousands to millions of very old stars
white dwarf
Small dense star
neutron star
smallest of all stars
apparent brightness
the brightness of a star when viewed from Earth
absolute brightness
Amount of light a star actually gives off
Hertzsprung-Russell diagram
chart that shows the relationship between the absolute magnitude and the surface temperature of stars
main-sequence star
star that falls in an area from the upper left corner to the lower right corner of the H-R diagram
parallax
The apparent change in position of a nearby star due to Earth's orbital motion around the sun
protostar
Early form of a star; This stage lies between the collapsing of dust and gas and the beginning of nuclear fusion
supernova
tremendous explosion in which a star breaks apart, releasing energy and newly formed elements
pulsar
a neutron star that produces radio waves
black hole
the final stage in evolution of a very massive star, where the core's mass collapses to a point that it's gravity is so strong that not even light can escape
telescope
A device built to observe distant objects by making them appear closer
visible light
Electromagnetic radiation that can be seen with the unaided eye
wavelength
the distance between the crest of one wave and the crest of the next wave
optical telescope
a telescope that uses lenses or mirrors to collect and focus visible light
electromagnetic radiation
energy that travels through space in the form of waves
refracting telescope
a telescope that uses convex lenses to gather and focus light
convex lens
a piece of transparent glass curved so that the middle is thicker than the edges
reflecting telescope
a telescope that uses a curved mirror to collect and focus light
radio telescope
a device used to detect radio waves from objects in space
observatory
a building that contains one or more telescopes
spectrograph
an instrument that separates light into colors and makes an image of the resulting spectrum
light-year
the distance that light travels in one year, about 9.5 million million kilometers
scientific notation
a mathematical method of writing numbers using the powers of ten
universe
all of space and everything in it
eclipsing binary
a binary star system in which one star periodically blocks the light from the other
Hubble's law
the observation that the farther away a galaxy is, the faster it is moving away
solar nebula
a large cloud of gas and dust, such as the one that formed our solar system
planetesimal
One of the small asteroid-like bodies that formed the building blocks of the planets
dark matter
matter that does not give off electromagnetic radiation but is quite abundant in the universe
dark energy
a mysterious force that appears to be causing the expansion of the universe to accelerate