Overview
This lecture explores the vast scale of the universe by comparing familiar objects and distances, showing how small humans are compared to astronomical structures.
Human and Everyday Scales
- A human is about 2 meters (6 feet) tall.
- Lying a person down 10 times equals the length of an 18-wheeler (~60 feet).
- Stacking 10 18-wheelers vertically equals a 60-story skyscraper.
- Ten skyscrapers laid end-to-end approximate the length of the Golden Gate Bridge (~1 mile).
- Multiplying by 10, a large city is roughly 10 miles across.
Expanding to Regional and Planetary Scales
- Multiplying city size by 10: the San Francisco Bay Area is about 100 miles across.
- Mulitply by 10 again: region as large as the western US (~1,000 miles across).
- Another factor of 10: slightly more than Earth ’s diameter (~8,000 miles).
- Earth’s diameter times 10 equals the diameter of Jupiter (~80,000 miles).
Comparing to Solar and Stellar Distances
- Jupiter’s diameter times 10 equals the Sun’s diameter (~800,000 miles).
- The distance from the Earth to Sun is 100 times the Sun’s diameter (93 million miles).
- The nearest star is 200,000 times farther than the distance between the Earth and Sun (4.2 light years).
Galactic and Universal Scales
- The Milky Way galaxy is about 100,000 light years in diameter.
- The distance to the nearest star multiplied by 25,000 equals the Milky Way’s diameter.
- The observable universe is about 93 billion light years across.
- The observable universe is over a million times larger than the Milky Way.
Key Terms & Definitions
- Light Year — the distance light travels in one year (~5.88 trillion miles).
- Observable Universe — the region of the universe from which light has reached us since the universe began.
- Diameter — the straight-line distance through the center of a circle or sphere.
Action Items / Next Steps
- Reflect on the scales discussed to better appreciate the vastness of the universe.