Section 10.2: Galaxies
Overview
- Galaxy Definition: A galaxy is a large collection of stars, gas, and dust bound by gravity. There are several billion galaxies in the universe, each potentially containing billions of stars. Our galaxy is the Milky Way.
- Nebula: Dense, cloud-like collections of gas and dust, sometimes where stars form.
Types of Galaxies
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Spiral Galaxies
- Resemble a pinwheel from above.
- Appear as a plate with a central ball when viewed from the side.
- Contain a significant amount of gas, dust, and young stars.
- Example: Milky Way.
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Elliptical Galaxies
- Shaped like a flattened sphere.
- Range from perfect spheres to stretched shapes like footballs.
- Comprise over half the galaxies in the universe.
- Have the oldest stars with minimal gas and dust.
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Irregular Galaxies
- Lack a distinct shape.
- Contain abundant gas and dust, essential for star formation.
Star Clusters vs. Galaxies
- Star Clusters: Groups of stars within galaxies.
- Globular Clusters: 100,000 to 1,000,000 stars, spherical shape.
- Open Clusters: Up to a few thousand stars of similar age.
Vocabulary
- Important terms: billion, dust, elliptical, galaxy, gas, globular, gravity, irregular, Milky Way, nebula, open, spiral, star clusters, stars, thousand.
Comprehension Questions
- What is a galaxy?
- What are the three basic shapes of galaxies?
- What type of galaxy is the Milky Way?
- Which type of galaxy contains the oldest stars in the universe?
- What is found in an irregular galaxy?
- What is the percentage of galaxies that are elliptical, approximately?
- What are the two types of star clusters?
- How do the two types of star clusters differ?
Galaxy Shapes Diagrams
- Spiral Galaxy: Describe the pinwheel shape and central ball.
- Elliptical Galaxy: Explain the range of shapes from sphere to football-like.
- Irregular Galaxy: Note the lack of a consistent shape and presence of gas and dust.
These notes provide a comprehensive overview of galaxy types, their characteristics, and the concept of star clusters.