I. Objective
When you look up at the planets and stars, you are seeing things that are very far away. The universe is a very big place. How big is it? If we were able to “zoom out," and look back in at the
Earth and at its place in the solar system, or look at the solar system in the galaxy, what would it look like? In this lab we will calculate the relative sizes of the various structures in the universe by making scale models.
We will try to comprehend the hugeness of space.
II. Exercises
We begin our exploration of the universe with the Earth: a ball of rock, mostly covered by water, that is
13,000 kilometers (km) in diameter. Gravity pulls things on the surface toward the center, and we live up on the surface.
Your instructor will show you something - a volleyball, an orange, maybe something really weird - that represents a scaled down model of the sun, if the instructor is not present then use 7 inches. In real life the sun is a huge ball of hydrogen gas 1,400,000 km in diameter. (or a little less than a million miles). a. Draw an Earth which is approximately the correct size relative to the model used for the sun. Explain your calculations and the scale transformations that you use to make this drawing.
The sun is 150,000,000 km away from the Earth (that's 150 million km). b. Using the same scale as for part a., determine the distance that should be between your drawing of the
Earth and the instructor's model of the sun. Explain your calculations.
Assign two volunteers to hold the Earth drawing and the model of the sun the correct distance apart.
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Now we'll use a smaller scale to visualize the solar system (the sun and its eight planets).
Below is a scale drawing of the “inner" solar system: the sun, Mercury, Venus, Earth, and Mars.
Astronomers often use a distance called the Astronomical Unit, or AU, to represent the average distance between the sun and the Earth (1 AU = 1.5 x 10 8 km). The “outer" planets are more distant from the sun, and would be located off the page: Jupiter, Saturn, Uranus, and Neptune.
c. If this drawing represents the “actual" size of the inner solar system, how far away would Jupiter (5.2 AU) be? How about Neptune (30.1 AU)? Name an object that's about the same size as the orbit of Neptune on this scale. Show all work, and be sure to explain how you got your answers.
The star Vega is one of the brightest in the summer sky. Its distance is so great that light itself, which travels
300,000 km every second, takes 27 years to travel from Vega to the Earth. Thus the distance to Vega is 27
“light years" (a unit of DISTANCE). The star Deneb appears almost as bright but is at least 1,600 light years away. Astronomical distances are enormous; light takes 8 minutes just to get from the sun to the Earth. Note therefore that 1 AU is equal to 8 “light minutes" or 0.000016 light years.

d. If the entire universe was shrunk down to the same scale as in part c., what would be the scaled distances to Vega and Deneb? That is, if you placed the sketch of the inner Solar System on the ground and had to walk the correct distance to get to Vega or Deneb, how many kilometers would you have to walk? Show all work and explain all of your calculations.
Also, please complete the following sentence: “To a make a scale model of our Solar System and the stars
Vega and Deneb, to the same scale as the diagram in part c., I would need to place the Sun in Glenwood
Springs, and the stars Vega and Deneb in (some town) and (some other town)."
All of the stars we can see in the sky are part of our Milky Way Galaxy, a huge collection of stars of diameter about 100,000 light years. All the stars in the Milky Way, including our sun, are held together by mutual gravitational attraction. The Milky Way would be disk shaped if we could travel outside it and look back, and brighter stars would form a nice spiral pattern when viewed from above. The sun is located about 2/3 of the way out from the center toward one side of the disk. A sphere of radius 1,600 light years (the distance to
Deneb) would enclose most of the stars we can see with the naked eye in the night sky. e. Choose a scale, and make a sketch of the Milky Way Galaxy on the back of this sheet. (You may represent the Milky Way as a plain old circle - nothing fancy is needed.) Put a dot where the sun should be, and draw a circle around the sun, whose radius is the correct scaled distance from the sun to Deneb. This circle represents our local neighborhood of stars that can be seen with the naked eye. Be sure to show how you determined the diameter of your Milky Way sketch, and the radius of your “circle around the sun."
Here you may draw your sketch for part e.
The observable universe is teeming with galaxies. Now, we think the universe is about 15 billion
(1.5 x 10 9 ) years old. (That's about 3 times the age of the Earth and Solar System, which we measure to be 4.6 billion years old.) Since light can only travel at the speed of light, and the universe did not exist more than 15 billion years ago, the farthest we can ever hope to see with the largest telescopes is 15 billion light years. In this sense, the radius of the sphere around us which is the observable universe is 1.5 x 10 9 light years. f. If the Milky Way Galaxy were as small as a piece of paper (20 cm in diameter), how far away would the most distant galaxy observable be located? Show your calculations clearly. g. Put it all together by imagining two trips by rocket or some other sort of spacecraft.
One is a trip to the sun. The other is a trip to the most distant observable galaxy.
How many times longer is the second trip? h. Summarize the facts and ideas presented, including any additional questions you may have.