light year, the distance that light travels in one year, nuclear fusion, a reaction in which two lighter nuclei fuse to form a heavier nucleus releasing energy, apparent magnitude scale, a scale for measuring the brightness of an object when viewed from Earth, absolute magnitude scale, a scale for measuring the brightness of an objects from the same distance, luminosity, the actual brightness of a star (the amount of energy it radiates) when measured using the absolute magnitude scale, Hertzsprung-Russell diagram, a graph displaying star data, with the stars' spectral class (temperature) on the x-axis, and its absolute magnitude (luminosity) on the y-axis, stellar parallax, a change in the apparent position of a star against its background when viewed from two different positions, nebula, a cloud of dust and gas in space, hydrostatic equilibrium, in relation to Earth's atmosphere: a state of stability, with upward forces balanced by downward forces, red giant, a star that has become large and bright with a cool surface because it has run out of hydrogen fuel, planetary nebula, a glowing shell of gas formed when a star dies, white dwarf, a small star that forms when a star (eg our sun) runs out of fuel and slowly fades and cools, black dwarf, remnants formed when a white dwarf star cools and gradually fades away, supernova, the explosive death of a star, neutron star, a small, highly dense star made mostly of neutrons, black hole, a region in space of infinite density where gravity is so strong that nothing, not even light, can escape from it, absorption spectrum, a spectrum with dark bands missing from the pattern, where the element has absorbed characteristic light wavelengths; the opposite of an emission spectrum, emission spectrum, the pattern of wavelengths or frequencies that appear as coloured lines in a spectroscope. It is unique to each element, Dopppler effect, the apparent change in wavelength (or frequency) when the source of the waves or the observer is moving, responsible for the red shift of distant stars, red shift, the apparent decrease in frequency (towards the red end of the spectrum) of light from galaxies that are moving away from earth, blue shift, the apparent increase in frequency (towards the blue end of the spectrum) of light from galaxies that are moving towards the earth, Big Bang Theory, the theory that the universe began as a hot, dense, single point at some time in the past, and since then, has expanded and will continue to expand into the future, Sun, our closest star, galaxy, huge collection of stars held together by gravity, star chart, map used to locate objects in the night sky, constellation, group of stars that are close together in the sky, universe, everything that exists in space, star, a celestial body appearing as a luminous point in the night sky, solar system, the Sun and all the planets, dwarf planets, moons and asteroids that travel around it and each other, ultraviolet radiation, invisible rays that are part of the energy that comes from the Sun

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