Download A Relative-Scaled Model of the Solar System

A Relative-Scaled Model of the Solar System
Today we’ll lay out the true distances of the Sun and planets as they occur in the Solar System,
but we’ll do it on a scale relative to one we can understand. An Astronomical Unit (AU) is the
distance from the Earth to the Sun. It is 9.3 x 107 miles or 1.5 x 108 km (recall that km are SI units
and miles are not). These numbers are very hard to grasp because we don’t deal with such large
units in our daily lives. So we’ll scale 1 AU down to 1 meter and lay the planets out
correspondingly.
What to do.
1. Get a handout for your group and cut out each individual planet and the Sun sized as a
basketball. Include the name to go with each planet as you cut carefully. Note that in our model
the Sun would not actually be the size of a basketball! It would only be about 2 cm in diameter!
2. Now the whole class will go outside to the front of the school. Get a meter stick and wait for
teacher instructions! While outside do not disturb any other classes or you will get a zero on
this activity!
3. With your group, find an area to lay out your solar system that will allow you to walk a long
line. Put the Sun down at the start of the line. Now walk the following distances from the Sun
and place the correct planet at the right location using your meter stick.
Mercury Distance = 30 cm. which is the same as 0.3 meters.
Venus Distance = 70 cm. which is the same as 0.7 meters.
Earth is 1 AU so it is exactly one meter.
Mars Distance = 1 meter and 50 cm. which is 1.5 meters.
Jupiter Distance = 5 meters
Saturn Distance = 10 meters
Uranus Distance = 20 meters
Neptune Distance = 30 meters
Pluto Distance = 40 meters
3. Now walk back to Earth. You’ll have some questions to answer in your group.
a. Standing at Earth, which planet is closest to you? Do you know why Venus is called Earth’s
twin?
b. If it were midnight on Earth and you facing away from the Sun, would you expect to see
Mercury or Venus in the midnight sky? Why or why not?
Venus is known to some people as the evening or morning star (recall that during Classical Greek
times the planets were known as the wandering stars). Why?
c. Mercury can sometimes be seen right before sunrise or just after sunset, but it is much harder to
see. Why?
d. How about the other planets? Might you possibly see them at midnight? How about right
before sunrise or right after sunset?
e. From Earth 5 planets were known since ancient times because they can be seen without a
telescope. Can you name them?
f. Water is a key ingredient for life. Which planet is known to have large surface bodies of water?
Water-ice is quite common in the solar system, however there are some bodies that are known to
have reservoirs of liquid water below their icy surfaces. Do you know which solar system bodies
these are? Where is the only place we know for sure that life exists in the solar system?
g. Now move midway between Mars and Jupiter. Do you know what solar system object is here?
(actually it’s a bunch of objects all orbiting the Sun) What fell out of this area and stuck Earth 65
million years ago? What happened?
h. Now walk out to Jupiter. This is the first of the Gas Giant planets. How are they different from
the inner planets (Mercury, Venus, Earth, Mars)?
i. Jupiter’s 4 largest Moon’s are named the Galilean Moons in honor of Galileo. Can you guess
why?
j. Now walk out to midway between Neptune and Uranus. These planets are about half the size
of Jupiter and Saturn and a darker blue color because they have methane in their atmosphere
which is a blue gas. Can you think of a place on Earth where methane comes from? Can you
explain why they are much harder to see without a telescope?
k. Now walk to Pluto. Pluto is a member of the Kuiper Belt which extends from just beyond
Neptune to as much as 50 AU’s from the Sun, and beyond that icy comets orbit the Sun as far out
as 100,000 AU’s. In our scale how far out would the Oort cloud be in meters?
l. Can you guess how far it is to the nearest star? It is a little over 4 light years away, but in our
model where 1 AU = 1 meter, the nearest star would be about 250,000 meters away. To get an
everyday sense of how far this is convert 250,000 meters to km. and then to miles by first
dividing 250,000 by 1000 and then multiply your answer by 0.62. Show your work by showing
the equation above with the answer.
m. You should have found that it’s 155 miles to the nearest star in our model! That would be like
driving from Fremont almost all the way to Yosemite or Lake Tahoe!
The distances to stars are so great that even with our fastest rocket ships it would take about
150,000 years just to arrive at the nearest star. And most stars that we see in the sky are hundreds
or thousands of light years away. Imagine how powerfully bright they are as they create new
atoms and the full spectrum of light energy in the process of nuclear fusion! The fact that we see
them at all from so very far away tells you how powerful they truly are! Our solar system is part
of the Milky Way Galaxy which is 100,000 light years across and contains some 300 billion stars.
The average distance between stars is about 5 light years and if we reduced the average size of a
star to a grain of sand then that distance between grains of sand “stars” would be 30 miles! Whoa.