SCI-103 Introductory Astronomy Summer 2012 Homework 1
Ratio problems
1. How many Earths could fit side by side across the Sun? Look up the radii of the Earth and Sun
Radius of the Earth = 6.378  10 6 m
Radius of the Sun = 6.96  108 m
The Ratio
384.4  10 6 m
 109
6.378  10 6 m
109 Earths could fit side by side across the Sun.
2. How many Earth’s could fit between the Earth and the Moon? Look up the distance to the Moon
Distance to the Moon = 384.4  10 6 m
Diameter of the Earth = 1.276  107 m
384.4  10 6 m
 30.1
The Ratio
1.276  10 7 m
About 30 Earths could fit side by side Between the Earth and the Moon.
3. How many Earth’s could fit between the Sun and the Earth? Look up the AU
1 AU = 1.5  1011 m
Diameter of the Earth = 1.276  107 m
The Ratio
1.5  1011 m
 11,755
1.276  107 m
Almost 12,000 Earths could fit side by side between the Earth and the Sun.
4. How many Suns could fit side by side across the solar system? Look up Pluto’s Distance from the
Sun
Pluto’s distance from the Sun = 39 AU = 5.85  1012 m
Diameter of the Sun = 1.39  109 m
5.85  1012 m
 4,209
The Ratio
1.39  109 m
About 4,200 Suns could fit side by side across our solar system.
5. How many solar systems could fit side by side between the Sun and the next nearest star Proxima
Centauri? Look up the distance to Proxima Centauri
Distance to Proxima Centauri = 4.3 ly = 4.07  1016 m
Diameter of the Solar System = 78 AU = 1.17  1013 m
4.07  1016 m
 3,479
The Ratio
1.17  1013 m
About 3,400 of our solar systems could fit side by side between the Sun and the nearest star
Proxima Centauri.
6. How many solar systems could fit side by side across the Milky Way galaxy? Look up the
diameter of the Milky Way galaxy.
Diameter of the Solar System = 78 AU = 1.17  1013 m
Diameter of the Milky Way = 100,000 ly = 9.46  10 20 m
9.46  10 20 m
 8.09  107  81 Million
The Ratio
13
1.17  10 m
About 81 Million of our solar systems could fit side by side across the Milky Way Galaxy.
Reflection Questions
What is your impression of the scale of the Universe after doing these calculations?
Which answer surprised you the most?