O,B,A,F,G,K,M. (each letter is also divided into 10 subdivisions)
the condition in which pressure and gravitational forces in a star or planet are in balance. Without such balance, bodies will either collapse or expand.
the lower part of the Sun's outer atmosphere that lies directly along the Sun's visible surface (photosphere)
a low-density region in the Sun's corona. The solar winds may originate in these regions.
the visible surface of the Sun, when we look at the Sun in the sky, we are seeing its photosphere.
the nuclear fusion process that converts hydrogen into helium in stars like the Sun and thereby generates their energy. This is the dominant energy-generation mechanism in cool, low-mass stars.
a sudden increase in brightness of a small region on the Sun. This flare is caused by a magnetic disturbance.
a dark, cooler region on the Sun's visible surface created by intense magnetic fields.
a binary star pair in which one star periodically passes in front of the other, totally or partially blocking the background star from view as seen from Earth.
inverse square law
(1.) any law in which some property varies inversely as the square of the distance, d. Mathematically as 1d (2) the law stating that the apparent brightness of a body decreases inversely as the square of its distance.
the region in the H-R diagram in which most stars, including the Sun, are located. The main sequence runs diagonally across the H-R diagram from cool, dim stars to hot, luminous ones. Stars on the main sequence fuse hydrogen into helium in their cores.
the shift in an objects position caused by the observer's motion a method for finding distance based on that shift.
the velocity of a body along the line of sight. that is the part of its motion directly toward or away from the observer.
a type of binary star for which the spectrum lines exhibit a changing Doppler shift as a result of the orbital motion of one star around the other.
a pair of stars held together by their mutual gravity and in orbit about each other, and that can be seen with a telescope as separate objects.
the rising and sinking motions in a liquid or gas that carry heat upward through the material. convection is easily seen in a pan of heated soup on a stove.
extremely energetic particles (protons, electrons, and so forth) traveling at nearly the speed of light. Some rays are emitted by the Sun, but most come from more- distant sources, perhaps exploding supernovas.
the time period from about A.D 1600 ti 1740 during which the Sun was relatively inactive. Few sunspots were observed during this period.
the binding of two light nuclei to form a heavier nucleus, with some nuclear mass converted to energy. For example, the fusion of hydrogen into helium. This process supplies the energy of most stars and is commonly called "burning" by astronomers.
the force exerted by a substance such as a gas on an area divided by that area.
the region inside a star where its energy is carried outward by radiation ( that is photons)
two or more stars in orbit around each other, held together by their mutual gravity.
the outflow of low-density, hot gas from the Sun's upper atmosphere. it is partially this wind that creates the tail of a comet, by blowing gas away from the comets immediate surroundings.
a star of large radius and large luminosity.
the amount of energy radiated per second by a body. For example, the wattage of a light bulb defines its luminosity stellar luminosity is usually measured in units of the Sun's luminosity ( app. 4 10 to the 26 power watts)
a unit of distance equal to about 3.26 light years defined as the distance at which an observer sees the maximum angle between the Sun and the Earth to be one arc second.
method of standard candles
a type of star or other astronomical body in which the luminosity has a known value, allowing its distance to be determined by measuring its apparent brightness, and applying the inverse-square law: cepheid variable stars, supernovas, so forth.
the time required for a repetitive process to repeat. for example, orbital period is the time it takes a planet or star to complete an orbit. pulsation period is the time it takes a star to expand and then contract back to its original radius.
a star whose luminosity changes over time.
a hot, thin column of gas in the Sun's chromosphere.
a small, dim star.
a graph on which stars are located according to their temperature and luminosity. Most stars on such a plot lie along a diagonal line, called the main sequence, which runs from cool, dim stars in the lower right, to hot, luminous stars in the upper left.
a unit for measuring stellar brightness. The smaller the magnitude, the brighter the star.
texture seen in the Sun's photosphere, granulation is created by clumps of hot gas that rise to the Sun's surface.
tiny neutral particles with little or no mass and immense penetrating power. These particles are produced in great numbers by the Sun and other stars as they fuse hydrogen into helium, and also by supernova explosions.
ideal gas law
perfect gas law= a law relating the pressure, density, and temperature of a gas. it states that the pressure is proportional to the density times the temperature.
a cloud of hot gas in the Sun's outer atmosphere. This cloud is often shaped like an arch, supported by the Sun's magnetic field.
the cyclic change in solar activity, such as sunspots and solar flares, rising and declining about every (11) years.
the outer, hottest part of the Sun's atmosphere.
a dense star whose radius is approximately the same as the Earth's but whose mass is comparable with the Sun's white Dwarfs burn no nuclear fuel and shine by residual heat. They are the end stage of stellar evolution for stars like the Sun.
a method for measuring distances this method is based on constructing a triangle, one side of which is the distance to be determined. that side is then calculated by measuring another side ( base line) and the two angles at either end of the base lines.
a cool, luminous star whose radius is much larger than the sun's
a relation between the mass and luminosity of main-sequence stars. Higher-mass stars have higher luminosity.