Astronomy-Chapter 4-Stars, Galaxies, and the Universe-w/o images
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44 terms
Terms | Definitions |
|---|---|
 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 |
| spectrum | the range of wavelengths of electromagnetic waves |
| 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 |
| constellation | an imaginary pattern of stars in the sky |
| spectrograph | 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 |
| light-year | the distance that light travels in one year, about 9.5 million million kilometers |
| parallax | the apparent change in position of an object when seen from different places |
| 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 |
| nebula | a large cloud of gas and dust in space, spread out in an immense volume |
| protostar | 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 |
| supernova | the brilliant explosion of a dying supergiant star |
| neutron star | the small, dense remains of a high-mass star after a supernova |
| pulsar | 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 |
| binary star | a star system with two stars |
| eclipsing binary | a star system in which one star periodically blocks the light from another |
| open cluster | a star cluster that has a loose, disorganized appearance and contains no more than a few thousand stars |
| globular cluster | a large, round, densely-packed grouping of older stars |
| galaxy | a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity |
| 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 |
| quasar | an enormously bright, distant galaxy with a giant black hole at its center |
| universe | all of space and everything in it |
| scientific notation | a mathematical method of writing numbers using powers of ten |
| big bang | the initial explosion that resulted in the formation and expansion of the universe |
| Hubble's law | the observation that the farther away a galaxy is, the faster it is moving away |
| cosmic background radiation | the electromagnetic radiation left over from the big bang |
| 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 |
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