Lesson 1 – Determining Our Sun’s Habitable Zone
Group name: ________________________________
In this lesson we will determine our Sun’s “habitable zone.” The habitable
zone is the distance from the Sun that the Earth can be and still support life on its
surface. Remember that all life that we know of requires liquid water to survive.
Therefore, we can define our habitable zone as the range of distances from the
Sun where the Earth’s average surface temperature is greater than 0ºC (the
melting point of water) but less than 100ºC (the boiling point). To find out
where this area is we will use the Planet Temperature Calculator. This program
figures out the average surface temperature of a planet based on information
about that planet that you enter.
The Planet Temperature Calculator looks at the MASS of the star that your
planet is orbiting, the DISTANCE from that star, the BOND ALBEDO (al-BEE-do)
of the planet and the GREENHOUSE EFFECT of the planet’s atmosphere. In the
last lesson we said that increasing the MASS of a star increases the energy that it
gives off (and reduces its life span). In later lessons we will look at the effects of
BOND ALBEDO and GREENHOUSE EFFECT on temperature. Today we will see
how the DISTANCE from the nearest star affects the temperature. We will enter
Earth-like values for MASS, BOND ALBEDO and GREENHOUSE EFFECT, enter
different values for DISTANCE, and record our results.
1) Open the planet temperature program:
www.astro.indiana.edu/~gsimonel/temperature1.html
2) Read the information on this screen and then click on the “continue” button.
This will bring you to the MASS screen. Read the information about MASS and
then , in the white box below the text, enter the number 1 and click the “next”
button next to the box.
3) This will bring you to the DISTANCE screen. Read the information about
DISTANCE, enter the number 1 in the white box, and click the “next” button.
4) This will bring you to the BOND ALBEDO screen. Read about BOND
ALBEDO, enter the number 29, and click the “next” button.
5) You should be at the GREENHOUSE EFFECT screen now. Read about the
GREENHOUSE EFFECT and enter the number 1 in the box. Then click the “next”
button.
6) This brings you to the “REVIEW” page. You can change any of the values that
you entered on this screen. Don’t make any changes yet, just click on the button
marked “calculate” in the bottom right corner of the screen.
7) This page tells you what the average surface temperature of your planet is
based on the numbers that you entered. If you entered the numbers correctly
you will see that the Earth has an average surface temperature of 15 ºC or 59 ºF.
You will also see, in the white box toward the center of the screen, that our Sun
has a life cycle of 10 billion years. That means that our Sun has enough fuel to
last 10 billion years. Since the Sun is around 4.7 billion years old, that means it will
last for another 5.3 billion years before it uses up all its nuclear fuel and dies in a
violent explosion.
Fill out the Habitable Zone Table.
8) Click the “return” button to go back to the REVIEW screen. Do not change
the values for MASS, BOND ALBEDO or GREENHOUSE EFFECT. Use the
Habitable Zone Table to find out what values to enter for DISTANCE. Start by
entering 0.1 for DISTANCE and click the CALCULATE button. Record the
SURFACE TEMPERATURE in degrees Celsius on the table in the box next to “0.1”
Be sure to record the temperature in degrees Celsius. This is the number in the
middle of the three stacked boxes.
9) Click the RETURN button. Enter 0.2 for DISTANCE and click the CALCULATE
button. Record the SURFACE TEMPERATURE in degrees Celsius on the table in
the box next to “0.2” Click the RETURN button.
10) Continue finding and recording the SURFACE TEMPERATURE for the rest of
the numbers on the table.
Make a chart in Microsoft Excel.
11) Start Microsoft Excel. Open a new file. In column A, enter “0.1” in space A1,
“0.2” in space A2, etc., down to “1.3” in space A13. In column B, enter the
temperatures from the Habitable Zone Table. Enter the first temperature in space
B1, the second temperature in space B2, etc.
12) On the menu bar, click on Insert>>Chart (or click on the Chart icon). This
opens up the Chart Wizard box.
13) Select the Line chart and click Next.
14) Click on the Data Range tab at the top of the Chart Wizard and then click on
the little data icon on the far right side of the white box in the middle of the
Wizard, next to the space marked Data Range. Click and drag your cursor over
spaces B1 through B13, and hit Enter. (Do not click Next yet.)
15) Now click on the Series tab. At the bottom of the box is a space marked
Category (X) axis labels. Click on the data icon to the right of this space. Click and
drag your cursor over spaces A1 through A13, and hit Enter. Click Next.
16) Click on the Titles tab. For the Chart title: type the name of your group and
then “The Sun’s Habitable Zone.” For Category (X) axis: type “Distance in
Astronomical Units (AU).” For Value (Y) axis: type “Temperature in Degrees
Celsius.” (Do not click Next yet.)
17) Click on the Gridlines tab. For Category (X) axis select “Minor gridlines.”
Check to make sure the “Major gridlines” is selected for Value (Y) axis. (Do not
click Next yet.)
18) Click on the legend tab. De-select “Show legend” by clicking on the box next
to “Show legend” so that the checkmark disappears. Click on Next.
19) For Place chart: select “As new sheet.” Click Finish. Print your chart.
20) At Earth’s normal atmospheric pressure, water freezes at 0ºCelsius (C) and
boils at 100ºC. The Sun’s habitable zone is the distance from the Sun where a
planet’s average surface temperature is between 0ºC & 100ºC. On your chart,
find the point where the line of the graph crosses the horizontal line for 100ºC,
and then check how far out on the X axis (Distance in AU) this is. This is the
inner limit of the Sun’s habitable zone. Next find the point where the line of the
graph crosses the horizontal line for 0ºC, then check how far out on the X axis
this point is. This is the outer limit.
21) Our Sun’s habitable zone inner limit is ______AU. If the Earth was any closer
to the Sun than this the liquid water on its surface would boil away.
The Sun’s habitable zone outer limit is ______AU. If the Earth was any farther
away from the Sun than this the liquid water on its surface would freeze.
If the Earth was outside of this habitable zone, chances are that life as we know
it would not be able to survive at the surface.
Habitable Zone Table
Distance from Sun, in
Astronomical Units (AU)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
Average Surface Temperature, in Degrees
Celsius