1. The TWO-INCH Universe
A powerful set of analogies to examine size and distance in astronomy
Source: smithsonianeducation.org

2. Earth’s diameter = 8,000 miles
QUESTION: If Earth is just two inches wide, how big would the Moon be at this scale?

3. Moon = ¼ inch! actual diameter = 2,000 miles
QUESTION: At this scale, how far apart should they be?

4. 5 feet! actual Earth-moon distance = 240,000 miles …1 light second!
QUESTION: How big should the sun be in this analogy?

5. A minivan (16 feet across)!
Actual Sun diameter = 875,000 miles
QUESTION: If the 2-inch Earth were placed in the middle of the classroom, where would the minivan need to be parked to represent the position of the sun at this scale?

6. 6 football fields away! The van could be parked at Family Fitness!
Actual Earth-Sun distance = 93,000,000 miles or 8 light minutes

7. NEW ANALOGY Scale down the minivan sun into a 2-inch sun
QUESTION: At this scale, how big would Earth be?

8. A grain of salt!
QUESTION: How big would the moon be?

9. A speck of dust!
QUESTION: How far away would this “speck of dust” moon be from the “grain of salt Earth”?

10. ½ inch!
QUESTION: How far away would the sun be from the “grain of salt” Earth?

11. 20 feet!

12. New Analogy: 2-inch Solar System
Sun speck in center, planets would be invisible at this scale!
Actual solar system size = 7,000,000,000 miles (10 light-hours)

13. Sun is 1 of billions of stars in our galaxy
Next nearest star at this scale (Proxima Centauri) would be 2 football fields away!
Actual distance = 25.8 trillion miles or 4.3 LY
Sun is 1 of billions of stars in our galaxy
QUESTION: At this scale, how big is the Milky Way?

14. About the size of North America
Actual Milky Way size = 100,000 LY
At this scale, if the tiny dot of light at the center of the solar system were a grain of salt, a teaspoon of the salt would represent about 100,000 of the Milky Way’s 200+billion stars!

15. New Analogy: The Realm of Galaxies
Side note: Andromeda galaxy is a galaxy that is very near the Milky Way and is seen as a single smeary light to the naked eye
Actual Andromeda size = 1.3 million trillion miles (220,000 LY)
Shrink the “continent-size Milky Way” down to 2-inches
QUESTION: If Milky Way is 2-inches big, what is the distance between these two galaxies?

16. ~ 5 feet!
Actual Milky Way-Andromeda distance = 15 million trillion miles (2.5 million LY)
At this scale, individual stars in these galaxies would not be visible even with a microscope
At this scale, the deep space galaxies seen by Hubble would be 4 miles from this classroom!
So…QUESTION: How big is the universe?

17. Fun things to consider….
Do you think it’s likely that there is life elsewhere among these incredible distances? How about intelligent life?
What would be some of the challenges in trying to communicate with other life around other stars?
Some people say they feel insignificant after understanding the scale of the universe. Others say it makes them feel that life on Earth is special, that the human mind has only grown more significant by understanding this vastness. What is your view?