Constellations. Seemingly fixed patterns of stars that shift across the sky.
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1. Collections of Stars Essential Skill 2-1:
Describe the three different types of galaxies, and identify the characteristics of our own Milky Way galaxy.
2. Constellations Seemingly fixed patterns of stars that shift across the sky.
“Fixed” because the stars are so far away they don’t appear to move.
Examples: Ursa Major (Big Dipper), Hercules, Orion, Cygnus, Lyra
4. Constellations, continued Stars in constellations are labeled according to apparent magnitude.
Apparent magnitude: how bright a star appears from our viewpoint here on Earth.
Assigned a number on a scale: lowest #s are brightest, highest are dimmest.
Faintest by telescope: 29.
Faintest by eye: 6
Some have negative values!! Negative values appear REALLY bright.
5. Galaxies Large groups of stars bound together by gravity.
Major component of universe; contain most of the visible mass of universe.
Typically 100,000 light years across, contain 100 billion stars (but they can be larger or smaller than this).
3 main types: spiral, elliptical, and irregular.
6. Spiral Galaxies Have a bright center of stars; black hole at center.
Flattened arms of stars spiral around center.
Contain millions of young stars, lots of gas and dust (star-forming regions)
Example: Milky Way galaxy, approximately 100,000 light years wide, 2,000 light years thick.
7. Elliptical Galaxies Very bright center (black hole at center)
No arms of stars
No young stars, very little gas and dust
8. Irregular Galaxies No particular shape
Smaller and fainter
No new stars
Possibly resulted from two galaxies colliding.