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- The galaxy that includes the solar system; appears as a hazy white band in the night sky.
- The milky way is about 100 000 light-years across.
- A huge collection of stars, planets, gas, and dust held together by gravity.
A collection of stars held together by gravity.
A collection of 50 to 1000 stars; open clusters appear along the main band of the milky way.
A collection of 100 000 to 1 000 000 stars, arranged in a spherical shape; globular clusters appear around the centre of the milky way.
- The small group of galaxies that includes the milky way.
A gigantic cluster of 4 to 25 clusters of galaxies, which is hundreds of millions light years in size.
Shapes of galaxies
- There are three types of galaxies:
- Spiral: when viewed from above they look like a pinwheel with many long “arms” spiraling out from the centre, when viewed from the side they look like plate with a bulge in the middle.
- Elliptical: range in shape from a perfect sphere to a stretched out ellipse, astronomers believe they contain some of the oldest stars in our galaxy.
- Irregular: they do not have any distinct shape, spirals, or bulge and contain both new and old stars.
- The study of the universe.
- Cosmologists try to answer questions like how did the universe begin, how is it changing, and will it someday end? Using telescopes and other technology they have been able to look back to right after the beginning of the universe.
- The change in frequency of a light source due to its relative motion to an observer; also, the change in pitch of a sound due to the motion of the source relative to an observer.
- For example as an ambulance approaches you the sound waves from the siren are compressed and you hear a higher pitch, then when the ambulance passes you the sound waves get lengthened and the pitch lowers.
The effect in which objects moving away from an observer have their wavelengths lengthened, toward the red end of the visible spectrum.
The effect in which objects moving toward an observer have their wavelengths shortened, toward the blue end of the visible spectrum.
- The event that may have triggered the expansion of the universe 14 billion years ago.
- According to the theory at this time jhe universe begin expanding with unimaginable violence from an incredibly hot and desne point.
Cosmic microwave background (CMB) radiation
- The radiation left over from the big bang, which fills the universe.
- When the universe begin it would have been filled with high-energy gamma rays with short wavelengths and as the universe expanded the wavelengths got stretched to the microwaves they are today.
- The most abundant form of matter in the universe; invisible to telescopes.
- Dark energy was hypothesized because when astronomers first predicted the speeds of stars in the Andromeda galaxy they found that the stars were moving much faster then predicted. According to their calculations of the galaxy's mass the stars should be flung out into space but they were not. Astronomers could explain the stars by assuming that the galaxy contains 90% more mass then accounted for by visible matter, since this mass doesn't emit or interact with light they called it dark matter.
A form of energy that makes up nearly three quarters of the universe; has the effect of increasing the expansion of the universe.