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Astronomy: Part 2
| Term | Definition |
|---|---|
| Photosphere | The visible surface of the Sun |
| Chromosphere | Thin layer of the Sun’s atmosphere that lies directly above the photosphere; glows red |
| Corona | Outermost layer of the Sun; a plasma that extends millions of kilometers into space |
| Solar Wind | High-speed protons and electrons that fly through the solar system from the Sun. The solar wind extends millions of kilometers out into space and can reach out into the solar system |
| Sunspot | Cool, dark area on the Sun’s surface that have lower temperatures than surrounding areas; sunspots usually occur in pairs and come and go on an 11-year cycle |
| Prominence | A stream of incandescent gas projecting above the sun's chromosphere. |
| Solar Flare | A violent explosion on the Sun’s surface. |
| Aurora | A natural electrical phenomenon characterized by the appearance of streamers of reddish or greenish light in the sky, usually near the northern or southern magnetic pole |
| Nuclear Fusion | The merging together of the nuclei of atoms to form new, heavier chemical elements; huge amounts of nuclear energy are released in the process |
| Constellation | A group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure. |
| Binary Star | A system of two stars in which one star revolves around the other or both revolve around a common cente |
| Light-Year | The distance light can travel in one year; 9.5 trillion kilometers |
| Apparent Magnitude | The magnitude of a celestial object as it is actually measured from the earth |
| Absolute Magnitude | The magnitude of a celestial object as it would be seen at a standard distance of 10 parsecs |
| Main-Sequence Star | A star that is fusing hydrogen atoms to helium; a star in the main portion of its “life" |
| Red Giant | Stage in a star's development when the inner helium core contracts while the outer layers of hydrogen expand |
| Supergiant | A very large star that is even brighter than a giant, often despite being relatively cool |
| Cepheid Variable | A variable star having a regular cycle of brightness with a frequency related to its luminosity, so allowing estimation of its distance from the earth |
| Nova | A star showing a sudden large increase in brightness and then slowly returning to its original state over a few months |
| Nebula | An interstellar cloud of gas and dust |
| Hertzsprung-Russell Diagram | A two-dimensional graph, in which the absolute magnitudes of stars are plotted against their spectral types. Stars are found to occupy only certain regions of such a diagram. |
| Protostar | A contracting mass of gas that represents an early stage in the formation of a star, before nucleosynthesis has begun |
| Supernova | A tremendous explosion that occurs when the core of a star is mostly iron |
| White Dwarf | A small to mid-sized star that has collapsed |
| Neutron Star | The remnant of a massive star after it explodes as a supernova |
| Pulsar | A celestial object, thought to be a rapidly rotating neutron star, that emits regular pulses of radio waves and other electromagnetic radiation at rates of up to one thousand pulses per second |
| Black Hole | The super dense core left after a supergiant explodes as a supernova |
| Galaxy | A very large group of stars held together by gravity; few million to a few billion stars |
| Hubble's Law | A law of cosmology stating that the rate at which astronomical objects in the universe move apart from each other is proportional to their distance from each other, 71 kilometers per second per megaparsec |
| Big Bang Theory | The hypothesis that all matter and energy were at one time compresses into a very small volume; then there was an explosion that sent everything moving outward, causing the universe to expand |
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3172004