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Unit 4 Semester 2
Astronomy
| Question | Answer |
|---|---|
| Doppler effect | the change in the observed frequency of a wave because of the motion of the source or the observer toward or away from the other; the frequency increases when the source and observer approach each other and decreases when they move apart |
| Doppler shift | apparent change in the wavelength of light, as seen by an observer, when the distance between the source and observer along the line of sight is changing |
| Hertzsprung Russell diagram | a diagram that shows the relationship among color, temperature, and brightness of stars |
| Kuiper Belt | a region beyond Neptune in which many thousands of small objects orbit; considered the source of short |
| Oort Cloud | a cloud of rocks and dust surrounding the solar system; considered the source of long |
| Roche limit | the lowest possible altitude at which a natural satellite can form and orbit, withstanding the gravitational force of the larger body |
| absorption spectrum | spectrum produced when specific wavelengths are absorbed when light from a continuous source passes through a given substance |
| adaptive optics | a process that removes distortions (such as those caused by the atmosphere) from a telescopic image in real time |
| aperture | the size of the main lens or mirror of a telescope |
| aphelion | the orbital point of an object in the solar system that is farthest from the sun |
| Apogee | for an object orbiting the earth, the point in its orbit farthest from the earth |
| astronomical unit | or AU; 1 AU is equal to the average distance from the earth to the sun, about 93 million mi (150 million km) |
| axis | an imaginary line through the center of a planet about which the planet rotates |
| big bang theory | the theory that states that the universe formed by rapid expansion of matter and energy from an initial infinitely small, dense point |
| black hole | a region in space where it is theorized that no mass or light can escape |
| bureaucratic waste | Unnecessary bureaucratic spending of money without providing real benefits. |
| chromosphere | the part of the atmosphere of the sun that is just above the photosphere |
| circumstellar disk | a broad ring of material orbiting a star |
| coma | the cloud of gas and dust surrounding the nucleus of a comet |
| comet | a body of ice, rock, and dust that orbits a star |
| convection | the process in which heat energy is transferred through the movement of matter |
| core | the center of the sun; the energy of the sun comes from nuclear fusion deep inside its core |
| corona | the outermost layer of the atmosphere of the sun |
| cosmology | the study, both in theory and by way of observation, of the space |
| density | a measure of how closely packed the particles in a substance are; the mass of an object divided by its volume |
| deuterium | an isotope of hydrogen with an atomic number of 1 and an atomic |
| dwarf planet | a body that is in orbit around the sun, has sufficient mass for its self |
| eclipse | the darkening of a planet, moon, or other object in space by the shadow of another object in space |
| ejecta | material thrown (ejected) from an impact crater during formation; ejecta may distribute around the crater in patterns (rays) and may build up the rim of the crater |
| electromagnetic energy | energy that moves as a wave at the speed of light |
| electromagnetism | the fundamental physical force that governs the electric and magnetic interaction of particles |
| ellipse | a closed geometric figure with two foci |
| emission spectrum | electromagnetic spectrum produced when the atoms or molecules of a transparent gas are excited |
| epicycle | a circular obit within an orbit |
| equinox | one of two times each year (about March 21 and September 23) when the sun crosses the equator and day and night are approximately equal length |
| extrasolar planets | planets orbiting a star other than the sun; that is, planets outside our solar system |
| frequency | the number of waves that pass through a point during a specific amount of time |
| galaxy | an enormous group of stars, dust, and gas all held together by gravity; the Milky Way is just one of many galaxies in our universe |
| geocentric | with the earth as the center |
| gravity | a physical force that pulls objects together; every bit of mass produces a gravitational force, which attracts all other masses; the more massive the object, the stronger its gravity |
| heliocentric | with the sun as the center |
| horizon | the line where the sky and earth appear to meet |
| ion tail | the part of a comet composed of ionized gases and created by interaction with the solar wind |
| iridium | a rare, hard, and heavy metallic element |
| kinetic energy | the energy of an object in motion |
| light year | the distance that light travels through space in one earth year; light travels through space at a speed of 186,000 miles per second |
| luminosity | the amount of energy radiated by a star |
| lunar eclipse | the darkening of part or all of the moon by the shadow of the earth, when the earth is between the sun and the moon |
| lunar month | the time it takes the moon to complete all its phases; the interval between successive new moons, 29.5 days |
| main sequence | a star that lies along a roughly diagonal line on a Hertzsprung Russell diagram; most stars spend most of their lives on the main sequence |
| nebula | a collection or cloud of interstellar gas and dust |
| neutrino | a particle with no electric charge and nearly no mass |
| neutron star | a very small, superdense star composed mainly of tightly packed neutrons |
| nuclear fusion | a reaction in which the nuclei of two elements combine to produce a nucleus of a heavier element and a great deal of energy |
| nucleus | of a comet, the frozen core (in the head of the comet), containing almost the entire cometary mass |
| orbit | the path an object takes as it revolves around another object |
| parallax | the apparent change in the position of a star that is caused only by the motion of the earth as it orbits the sun |
| parsec | unit of distance equal to 3.26 light years; it is the distance at which a star would have a parallax of 1 second of arc |
| penumbra | the outer, larger, less dark part of the shadow cast by one space body onto another |
| perigee | for an object orbiting the earth, the point in each orbit closest to the earth; perigee varies a small amount from orbit to orbit |
| perihelion | the orbital point of an object in the solar system that is closest to the sun |
| photosphere | the very thin layer of gas that makes up the visible surface of the sun |
| planetesimals | small bodies orbiting the sun, thought to have formed when the solar system formed and which may have formed the planets |
| posigrade motion | orbital motion in the same direction as is normal to bodies in a given system |
| positron | a particle with the same mass as an electron, but with a positive charge |
| protogalactic cloud | a massive gas cloud that collapsed to form a galaxy |
| protostar | a star that is forming; nuclear fusion has not yet begun |
| reflection | process whereby light bounces back from an object at the same angle and intensity that the object received it |
| refraction | the bending of light as it moves from one medium to another |
| retrograde motion | temporary reversal of apparent motion of an orbiting object |
| revolution | the action of one object going around another in an orbit or elliptical course |
| solar eclipse | the darkening of a place on the earth by the shadow of the moon, when the moon is between the sun and the earth |
| solstice | when the day is either at its greatest (summer solstice) or least (winter solstice) in duration |
| spectrogram | an image (map, picture, photograph) of a spectrum, usually produced by a spectrograph |
| spectrograph | a spectroscope (instrument for producing and observing a spectrum) designed to map and photograph a spectrum |
| spectroscopy | the production and observation of a spectrum as well as all associated methods of recording and measuring, including the use of a spectroscope (the instrument used to produce and observe a spectrum) |
| spectrum | the distribution of energy given off by a light source such as a star, arranged in order of wavelengths |
| supernova | a large explosion caused by the collapse of a massive star |
| tides | the rise and fall of water levels due to gravitational forces |
| umbra | the inner, darkest, cone shaped part of the shadow cast by one space body onto another |
| wave | a disturbance that travels through a medium transporting energy from one location to another location |
| wavelength | in transverse waves, the horizontal distance between one wave crest or trough and the next |
| zenith | the point directly overhead in the sky |
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