Download Read the information on Hertzsprung

Lesson 1
Hertzsprung-Russel Diagrams
Read the information on Hertzsprung-Russel diagrams and answer the questions
below.
Are all stars the same? Not in the least! Some stars are just beginning to form in nebulae, others are
enjoying middle age along the main sequence, and some have begun to die. The Hertzsprung - Russell
diagram is a tool that shows relationships and differences between stars. It is something of a "family
portrait." It shows stars of different ages and in different stages, all at the same time. But it is a great tool
to check your understanding of the star life cycle. Let’s go over the basics before we check your
understanding.
In the Hertzsprung-Russell (HR) diagram, each star is represented by a dot. There are lots of stars out
there, so there are lots of dots. The position of each dot on the diagram tells us two things about each star:
its luminosity and its temperature.
The vertical axis represents the star’s luminosity. Luminosity is technically the amount of energy a star
radiates in one second, but you can think of it as how bright or how dim the star appears. The luminosity
scale is a "ratio scale" in which stars are compared to each other based upon a reference (our sun).
The horizontal axis represents the star’s surface temperature (not the star’s core temperature – we cannot
see into the core of a star, only its surface)! Usually this is labelled using the Kelvin temperature scale. But
notice: In most graphs and diagrams, zero (or the smaller numbers) exists to the left on the diagram. This is
not the case here. On this diagram, the higher (hotter) temperatures are on the left, and the lower (cooler)
temperatures are on the right.
So how do you read the HR diagram? Well, let’s look at some basic regions on it. A star in the upper left
corner of the diagram would be hot and bright. A star in the upper right corner of the diagram would be
cool and bright. The Sun rests approximately in the middle of the diagram, and it is the star which we use
for comparison. A star in the lower left corner of the diagram would be hot and dim. A star in the lower
right corner of the diagram would be cold and dim.
Questions
1. What is a Hertzsprung-Russel diagram?
2. What does each dot on a Hertzsprung-Russel diagram represent and what information does it give
you?
3. What does “Luminosity” mean?
4. Why do we say the Luminosity is a “ratio scale”?
5. Which property of star’s is shown in a Hertzsprung-Russel diagram, core temperature or surface
temperature, and why?
6. Which temperature scale is used for the Hertzsprung-Russel diagram?
7. Why do we put our Sun in the middle of the Hertzsprung-Russel diagram?
For the next questions you will need to do a Google search for a picture of a Hertzsprung-Russel diagram
and copy-paste it below.
DOWNLOAD AND PASTE YOUR HERTZSPRUNG-RUSSEL DIAGRAM HERE
Describe the Luminosity and Surface Temperature of a star located on the Hertzsprung-Russel diagram in
the:
8. Top right corner
9. Bottom left corner
10. Bottom right corner
Interactive Lab
Let’s see how good you are at reading the HR diagram. Ctrl-Click the diagram below to
open the Interactive Lab. We are given five stars on a Hertzsprung-Russel diagram. Use
the drop boxes to describe the brightness and surface temperature to describe each star.
Once you have answered the Interactive Lab and have checked that your answers are
correct, take a screenshot of the Lab and paste it in the space below.
PASTE YOUR ANSWERS HERE
Are there any stars that seem out of place? WRITE YOUR ANSWER HERE For example,
are there any stars that are really hot but not very bright? WRITE YOUR ANSWER HERE
Are there any stars that are not very hot but they shine very brightly? WRITE YOUR
ANSWER HERE What do you think could account for these differences in stars that do not
fit the pattern? WRITE YOUR ANSWER HERE Stars that do fit the pattern are called main
sequence stars. Let’s look at those before we deal with the exceptions.
Most of the stars lie within a region called the main sequence. It looks kind of like a curved
line sloping from the upper-left to the lower-right of the HR diagram. There are some stars
that are not on the main sequence, but for now let’s concentrate on the main sequence
stars. Why do you think there is there a main sequence region anyway? WRITE YOUR
ANSWER HERE
COMPARE YOUR ANSWERS WITH THE TEXT BELOW BY TURNING OFF THE
HIGHLIGHTING OR CHANGING THE TEXT COLOUR FROM THE HOME TAB.
Well, there is a predictable relationship between the brightness and size of a star. This
shows up on the HR diagram. We know that hotter things are brighter. A hotter
temperature means that more energy is radiated into space. Bigger stars are brighter. A
bigger surface area means that more energy is radiated into space.
Lesson 2
Applications of Hertzsprung-Russel diagrams
In this lesson we are going to make a greater use of the Hertzsprung-Russel (HR) diagram.
Open the Interactive Lab by Ctrl-Clicking on the image below. The Interactive Lab will ask you 17 multiple
choice questions on interpreting HR diagrams and will not let proceed until you get the question right. Each
question is reproduced below and as you answer each question in the Interactive Lab draw a box around
the correct answer below.
Question 1:
Question 2:
Question 3:
Question 4:
Question 5:
Question 6:
Question 7:
Answer the final 4 short answer questions and take a screenshot of the final page and paste it below
along with the printout your answers that the Interactive Lab will provide.
COPY AND PASTE THE FINAL SCREEN OF THE INTERACTIVE LAB HERE
COPY AND PASTE THE PRINTOUT OF YOUR SHORT RESPONSE ANSWERS HERE
Open the following URL in your web browser
http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html
Read the information on the webpage and view the interactive animation and complete the Interactive Lab
with questions at the bottom of the page. When you have finished the questions, take a screenshot of the
final page and paste it below.
COPY AND PASTE THE FINAL SCREEN OF THE INTERACTIVE LAB HERE