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Astronomy Vocabulary Cheat Sheet by

Revision Sheet by Amber for 9H 2021, Unit 6.2-6.5 Astronomy Portfolio

6.2 Galaxies - Vocabulary

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.
The distance that light travels in a year (9,500­,00­0,0­00,000 km).
Approx. 3.26 light-­years.
The effect where an object appears to move when viewed from two different positions.
A group of stars held together by their gravity, galaxies form three shapes, ellipt­ical, spiral and irregular.
An imaginary picture in the night sky made up of stars.

6.3 Life Cycle of a Star - Vocabulary

A cloud of gas and dust held together by the gravity of the hydrogen atoms within it.
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.
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.

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.

6.5 The Big Bang Theory

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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