6.2 Galaxies - Vocabulary
Star |
A giant ball of hot, glowing gases (usually hydrogen & helium) |
Nuclear Fusion |
A process where the nuclei of atoms join and emit energy as light, heat and other electromagnetic radiation. |
Apparent Magnitude Scale |
A measurement of a celestial object's brightness when viewed from Earth (the more positive the number the dimmer the star). |
Absolute Magnitude Scale |
A measurement of a celestial object's brightness if viewed from the same distance; a measure of a celestial object's actual brightness or luminosity. |
Hertzsprung-Russel Diagram (HR) |
A graph that plots a star's temperature on the x-axis and absolute magnitude on the y-axis. |
Main Sequence |
A diagonal band most stars fall into when plotted on the HR Diagram.. |
Speed of Light |
Light travels at 300,000 km/s. |
Light-Year |
The distance that light travels in a year (9,500,000,000,000 km). |
Parsec |
Approx. 3.26 light-years. |
Parallax |
The effect where an object appears to move when viewed from two different positions. |
Galaxy |
A group of stars held together by their gravity, galaxies form three shapes, elliptical, spiral and irregular. |
Constellation |
An imaginary picture in the night sky made up of stars. |
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6.3 Life Cycle of a Star - Vocabulary
Nebula(e) |
A cloud of gas and dust held together by the gravity of the hydrogen atoms within it. |
Protostar |
When the center of a nebula heats up and pressure increases. |
Hydrostatic Equilibrium |
The balance of the forces of a star's gravity and energy output. |
Red giant |
Hydrogen decreases, gravity is stronger than energy output, a new type of nuclear fusion begins, releasing more energy, reaching a new hydrostatic equilibrium and cooling to red. |
Planetary Nebula |
Helium supply decreases in a red giant and the outer region fades to a shell. |
White Dwarf |
The core of a planetary nebula continues nuclear fusion, increases energy rate and temperature to get a small, white hot star. |
Black Dwarf |
The result of a white dwarf cooling and fading away. |
Red Supergiant |
A continuation of the red giant until iron is formed, resulting in a much larger, red star. |
Supernova |
The event where a red supergiant runs out of energy and collapses, resulting in a large explosive death. |
Neutron Star |
The aftermath of a supernova with a mass of less than 3 solar masses, an incredibly dense star with a diameter of only tens of kilometers. |
Black Hole |
The result of a supernova with a mass greater than 3 solar masses, a region of space with an extraordinary gravitational pull and density that even light cannot escape. |
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6.4 Moving Galaxies
Absorbtion Spectrum |
A spectrum with lines missing from the pattern due to elements of the star absorbing their light wavelengths, therefore removing them from the spectrum. |
Emission Spectrum |
The pattern of wavelengths (or frequencies) that appear as coloured lines on a spectrascope; the light wavelengths that are emitted from certain gases when they return to a stable state. |
Doppler Effect |
The effect that occurs when an object is moving slower than the speed of sound; waves in front of the object compress while waves behind disperse. |
Red Shift |
An increase in wavelength of radiation emitted by a celestial body which shifts the absorption spectra in the red direction of the spectrum, indicating that the object is moving away from the Earth. |
Blue Shift |
A decrease in wavelength of radiation emitted by a celestial bosy which shifts the absorption spectra in the red direction of the spectrum, indicating that the object is moving towards the Earth. |
Huibble's Law |
The further the galaxy, the higher the tendency to have a more red-shifted spectra; the ffurther the galaxy, the faster it was moving away. |
Big Bang Theory |
the theory that the universe began from a hot dense state which has continued to expand and will continue to do so. |
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6.5 The Big Bang Theory
Singularity |
A single, dense, hot point. |
Cosmic Microwave Background Radiation |
A form of electromagnetic radiation in the microwave spectrum left over from the formation of the Universe; evidence of the Bug Bang theory. |
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