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ASTRONOMY STAR DICTIONARY 

 

absolute magnitude - a scale for measuring the actual brightness of a celestial object without accounting for the distance of the object. Absolute magnitude measures how bright an object would appear if it were exactly 10 parsecs (about 33 light years) away from Earth. On this scale, the Sun has an absolute magnitude of +4.8 while it has an apparent magnitude of -26.7 because it is so close.
alpha centauri - other than the sun, the closest bright star to our solar system.
apastron - the point of greatest separation of two stars, such as in a binary star system.
astrochemistry - the branch of science that explores the chemical interactions between dust and gas interspersed between the stars.
atmosphere - one atmosphere is 14.7 pounds per square inch (105 Newtons per square meter); the average atmospheric pressure at sea level on Earth. Atmosphere is also a layer of gases surrounding a planet, moon, or star. The Earth's atmosphere is 120 miles thick and is composed mainly of nitrogen, oxygen, carbon dioxide, and a few other trace gases.
binary stars - a system of two stars that revolve around a common center of gravity.
constellation - a grouping of stars that make an imaginary picture in the sky. There are 88 constellations.
convective zone - where convection currents carry energy toward the surface
core - where the nuclear fusion reactions occur
declination (DEC)- the angular distance of an object in the sky from the celestial equator.
distance - how far it is from us
Doppler shift - occurs when sound is generated by, or reflected off of, a moving object. By measuring the star's spectrum and comparing it to the spectrum of a standard lamp, then the amount of the Doppler shift can be measured. The amount of the Doppler shift tells us how fast the star is moving relative to us. In addition, the direction of the Doppler shift can tell us the direction of the star's movement. If the spectrum of a star is shifted to the blue end, then the star is moving toward us; if the spectrum is shifted to the red end, then the star is moving away from us. Likewise if a star is spinning on its axis, the Doppler shift of its spectrum can be used to measure its rate of rotation.
double star - a grouping of two stars. This grouping can be apparent, where the stars seem close together, or physical, such as a binary system.
emission nebula - a type of nebula that shines by emitting light when electrons recombine with protons to form hydrogen atoms. The electron frequently approaches the proton in steps emitting energy as light as it gets pulled in. In one of the most common "steps," the recombining electron emits a photon of red light. Since many atoms in the nebula do this all at once, the nebula appears red in color. This type of nebula is created when energetic ultraviolet light from a hot star shines on a cloud of hydrogen gas, stripping away electrons from the atoms (ionization). The free electrons can then begin the process of recombination.
evolved star - a star that is near the end of its life cycle where most of its fuel has been used up. At this point the star begins to loose mass in the form of stellar wind.
flare star - a member of a class of stars that show occasional, sudden, unpredicted increases in light. The total energy released in a flare on a flare star can be much greater that the energy released in a solar flare.
fusion - a process where nuclei collide so fast they stick together and emit a great deal of energy. In the center of most stars, hydrogen fuses together to form helium. Fusion is so powerful it supports the star's enormous mass from collapsing in on itself, and heats the star so high it glows as the bright object we see today.
galactic nucleus - a tight concentration of stars and gas found at the innermost regions of a galaxy. Astronomers now believe that massive black holes may exist in the center of many galaxies.
galaxy - a large system of about 100 billion stars. Our Sun is a member of the Milky Way Galaxy. There are billions of galaxies in the observable universe. Exactly when and how galaxies formed in the Universe is a topic of current astronomical research. Galaxies are found in a variety of sizes and shapes. Our own Milky Way galaxy is spiral in shape and contains several billion stars. Some galaxies are so distant their light takes millions of years to reach the Earth. Galaxies are classified in three main groups; spirals, ellipticals and irregulars.
giant molecular cloud (GMC) - massive clouds of gas in interstellar space composed primarily of hydrogen molecules. These clouds have enough mass to produce thousands of stars and are frequently the sites of new star formation.
globular cluster - a tight, spherical grouping of hundreds of thousands of stars. Globular clusters are composed of older stars, and are usually found around the central regions of a galaxy.
heliopause - the point at which the solar wind meets the interstellar medium or solar wind from other stars.
H II region - a region of hot gas surrounding a young star or stars that is mostly ionized. The energetic light from these young stars ionizes the existing gas. This region typically appears red as it glows with the photons emitted when elections recombine with hydrogen protons.
H-R diagram - The Color-Magnitude Diagram is a graph upon which stars are plotted by spectral type and actual luminosity. It is named for the two scientists Russell and Hertzsprung who first used it in 1913.
hydrogen - the lightest and most abundant element. A hydrogen atom consists of one proton and one electron. A hydrogen nucleus is just a single proton. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth. Hydrogen is the building block of the universe. Stars form from massive clouds of hydrogen gas. hydrogen - the lightest and most abundant element. A hydrogen atom consists of one proton and one electron. A hydrogen nucleus is just a single proton. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth. Hydrogen is the building block of the universe. Stars form from massive clouds of hydrogen gas. Hydrogen is the building block of the universe. Stars form from massive clouds of hydrogen gas. hydrogen - the lightest and most abundant element. A hydrogen atom consists of one proton and one electron. A hydrogen nucleus is just a single proton. Hydrogen composes about 75 percent of the Sun but only a tiny fraction of the Earth. 
interstellar medium - the gas and dust that exists in open space between the stars.
luminosity - how much energy it puts out in a given time. luminosity = brightness x 12.57 x (distance)2. The larger a star (i.e., more massive) is, the more luminous it is (luminosity = mass3).
magnitude - The degree of brightness of a star or other object in the sky according to a scale on which the brightest star has a magnitude -1.4 and the faintest visible star has magnitude 6. Sometimes referred to as apparent magnitude. In this scale, each number is 2.5 times the brightness of the previous number. Thus a star with a magnitude of 1 is 100 times brighter than on with a visual magnitude of 6.
Messier, Charles - while hunting for comets in the skies above France, 18th century astronomer Charles Messier made a list of the positions of about 100 fuzzy, diffuse looking objects which appeared at fixed positions in the sky. Although these objects looked like comets, Messier knew that since they did not move with respect to the background stars they could not be the undiscovered comets he was searching for. These objects are now well known to modern astronomers to be among the brightest and most striking gaseous nebulae, star clusters, and galaxies. Objects on Messier's list are still referred to by their "Messier number". For example the Andromeda Galaxy, the 31st object on the list, is known as M31.
meteor - a small particle of rock or dust that burns away in the Earth's atmosphere. Meteors are also referred to as shooting stars
parallax - triangulation - Used to measure the distance of the star from the earth. The earth's orbit around the sun has a diameter of about 186 million miles (300 million kilometers). By looking at a star one day and then looking at it again 6 months later, an astronomer can see a difference in the viewing angle for the star. With a little trigonometry the different angles yield a distance. This technique works for stars within about 400 light years of earth.
photometer - used on the end of a telescope to measure the brightness of a star.
radiative zone - where photons carry energy away from the core
right assension (RA) - the amount of time that passes between the rising of Aries and another celestial object. Right ascension is one unit of measure for locating an object in the sky.
stars -  large balls of gases. New stars form from large, cold (10 degrees Kelvin) clouds of dust and gas (mostly hydrogen) that lie between existing stars in a galaxy.
Stefan-Boltzmann Law - This is the relationship between luminosity (L), radius (R) and temperature (T):  L = (7.125 x 10-7) R2 T4.            Units: L - watts, R - meters, T - degrees Kelvin
Temperature and Spectrum - Some stars are extremely hot, while others are cool. You can tell by the color of light that the stars give off. If you look at the coals in a charcoal grill, you know that the red glowing coals are cooler than the white hot ones. The same is true for stars. A blue or white star is hotter than a yellow star, which is hotter than a red star. So, if you look at the strongest color or wavelength of light emitted by the star, then you can calculate its temperature (temperature in degrees Kelvin = 3 x 106/ wavelength in nanometers). A star's spectrum can also tell you the chemical elements that are in that star because different elements (for example, hydrogen, helium, carbon, calcium) absorb light at different wavelengths.

 

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