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Unit 2 part 2
science
| Term | Definition |
|---|---|
| Photosphere | the region of the Sun that radiates energy to space; visible surface of the Sun |
| Chromosphere | the first layer of the solar atmosphere found directly above the photosphere |
| Corona | the outer weak layer of the solar atmosphere |
| Solar Wind | streams of protons and electrons ejected at high speed from the solar corona |
| Sunspot | a dark spot on the sun, which is cool by contrast to the surrounding photosphere |
| Prominence | a concentration of gases above the solar surface that appears as a bright archlike structure |
| Solar Flare | a sudden and tremendous eruption in the solar chromosphere |
| Aurora | a bright display of ever-changing light caused by solar radiation interacting with the upper atmosphere in the region of the poles |
| Nuclear fusion | the way in which the sun produces energy; Nuclear fusion occurs when less massive nuclei combine into more massive nuclei, releasing tremendous amounts of energy |
| Constellation | an apparent group of stars originally named for mythical characters; The sky is presently divided into 88 constellations |
| Binary star | one of two stars revolving around a common center of mass under their mutual gravitational attraction |
| Light-year | the distance light travels in a year, about 9.5 trillion kilometers |
| Apparent magnitude | the brightness of a star when viewed from Earth |
| Absolute magnitude | the apparent brightness of a star if it were viewed from a distance of 32.6 light-years; used to compare the true brightness of stars |
| Main-sequence star | a star that falls into the main sequence category on the H-R diagram; This category contains the majority of the stars and runs diagonally from the upper left to the lower right on the H-R diagram |
| Red Giant | a large, cool star of high luminosity; a star occupying the upper-right portion of the H-R diagram |
| Supergiant | a very large, very bright red giant star |
| Cepheid variable | a star whose brigthness varies periodically because it expands and contracts; a type of pulsating star |
| Nova | a star that explosively increases in brightness |
| Nebulae | a cloud of gas and/or dust in space |
| Hertzsprung-Russell Diagram | a two dimentional graph in which the absolute magnitudes of stars are plotted against their spectral types |
| Protostar | a collapsing cloud of gas and dust destined to become a star; a developing star not yet hot enough to engage in nuclear fusion |
| Supernova | an exploding star that increases in brightness many thousands of times |
| White dwarf | a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size, believed to be near its final stage of evolution |
| Neutron star | a star of extremely high density composed entirely of neutrons |
| Pulsar | a variable radio source of small size that emits radio pulses in very regular periods |
| Black hole | a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light |
| Galaxy | a group of stars, dust, and gases held together by gravity |
| Hubble's law | a law that statesthat the galaxies are retreating from the Milky Way at a speed that is proportional to their distance |
| Big Bang Theory | the theory that proposes that the universe originated as a single mass, which subsequently exploded |
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