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LAB ACTIVITY

"THE H-R DIAGRAM"

PURPOSE: To find out how brightness and temperature of stars compare with that of our sun.

FYI:

Astronomers have found that a relationship exists between the color of a star and its surface temperature. The temperature color chart (chart A ) shows this relationship. You will notice when looking at ( chart A ) that as temperature changes so does the color. You will also note that the temperature is not being measured in conventional units of Fahrenheit, or centigrade. Instead the temperature scale we will use in this lab is called the Kelvin scale ( K). The reason this scale is used is so that no negative numbers are used. The Kelvin scale starts at zero.

The luminosity of a star is the actual brightness of a star, that a star emits from its surface. The luminosity of our sun remains a constant of 1 (one). By using our sun as a constant we can better assign a value of luminosity to other objects in the night sky.

In this lab activity you will be plotting stars on a graph and plotting their surface temperatures, luminosity, and how they compare.

DIRECTIONS: READ THE FOLLOWING DIRECTIONS CAREFULLY.

1. You will NOT be working with a partner or anyone else during this lab.

2. On your color chart (chart A) find the temperature that fits the stars on ( chart B). For example on chart B, the star Betelgeuse has a surface temperature of 3,100 degrees K. On the color chart ( chart A ) the temperature falls into the RED category for that star. On chart B to the right hand side you have a blank area that you should place the color of the star according to the colors on chart A. Beside Betelgeuse you should put RED in the color area because its surface temperature falls into the red color area on chart A. SO FILL IN THE APPROPRIATE COLOR FOR THE STAR ACCORDING TO THE SURFACE TEMPERATURE.

3. Once you have filled out the chart (chart B) with the color of each star from chart A. Check your work, and make sure that you've filled out the data correctly.

4. Now we are ready for the next step. Setting up a graph:

Setting up a graph is not as easy as it looks so you want to pay attention ! You will be setting up your graph on graph paper after you have sketched a rough draft first. Your graph should consist of 2 axis. A vertical axis (Luminosity) and horizontal axis ( Temperature).

You will use the lowest and highest luminosities from Chart B to set your vertical scale. This scale increases from the bottom of the graph upward like the numbers on the example above. The only difference would be that your graph will have much higher numbers at the top than the example. You will use the lowest and the highest temperatures in Chart B to set the horizontal scale of the graph. ( Mr. Andrews will show you an example on an overhead in class). YOU WILL NOT use exact figures to plot exact points. (Mr. Andrews will explain in class).

 

After you have plotted all the points on your graph and labeled each star, read, and do the following:

  1. 1. Red giants have a relatively high luminosity (usually more that 100 times our sun) and a relatively low surface temperature( 2000-6000 degrees K). Draw a line that encloses all the stars that appear to have all the characteristics of a red giant, and label this area red giants.
  2. 2.A white dwarf is a star with low luminosity( about 100 times less that our sun) and a relatively high surface temperature(7500-20000 degrees K). Draw a square around a point that best depicts all the characteristics of a white dwarf, and label this area....W hite Dwarfs.
  3. 3.You will find while doing this lab activity that most of the stars are found in the middle in an area called the main sequence. The range of the temperatures and luminosities of these stars is great. Unlike the red giants and the white dwarfs the temperatures, and luminosities of main sequence stars seem to be directly related. The main sequence stars that have high luminosity also have high temperatures and vice versa. Draw a circle around the area that encloses all the stars that seem to have characteristics like main sequence stars.

Analysis and Conclusions(Click to download a copy)