Acknowledgement This activity is adapted from \"The Life Cycles of Stars\" devel

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Acknowledgement This activity is adapted from "The Life Cycles of Stars" developed for Project ASTRO NOVA by the Planetarium at Raritan Valley Community College (The New Jersey Astronomy Center for Education at Raritan Valley Community College, Somerville, NJ 08876-1265). Objective Students leam about these important properties shared by all stars: luminosity (brightness), temperature, and color. Background In the early 20h century (around 1910), Swedish astronomer Ejnar Hertzsprung and American astronomer Henry Norris Russell plotted the colors (temperatures) of stars against their luminosities (or brightness). " The resulting graph represented a huge leap forward in understanding stellar evolution, or the "lives of stars." Luminosity (usually plotted on the vertical or y-axis) is given in terms of the Sun's luminosity (either multiples or a * Celestial objects appear in a vast range of brightness. For example our Sun appears 16 trillion times brighter than the The color and temperature of stars are usually plotted on the x-axis, with high temperatures to the left and low to the right. All temperatures are given in K, or Kelvin degrees. fractional part). Sometimes luminosity is replaced by the absolute magnitude of the star. faintest stars visible to the naked eye. Clearly, some other means of expressing astronomical brightness is needed. Astronomers have developed what is called the magnitude scale: a logarithmic scale in which a difference of exactly 5 magnitudes corresponds to a factor of 100 in brightness. Each magnitude corresponds to a factor of 2.512 in brightness because 2.512 × 2.512 × 2.512 × 2.512 × 2.512-100. The magnitude scale runs from large positive numbers for very faint objects to negative numbers for very bright objects. For example a star of magnitude 5 is 100 times fainter than a star of magnitude 0. A star of magnitude-1 is 2.512 times brighter than a star of magnitude 0. Your H-R diagram will use magnitudes. Construct a Hertzsprung-Russell Diagram [40 pts] INSTRUCTIONS FOR INDIVIDUAL H-R DIAGRAM 1. An individual H-R diagram can be found on page 2. Star sizes for this smaller H-R diagram are found at the bottom of page 5. From the list of 90 stars, choose at least 40, divided as follows: 7 [size 1]; 8 [size 2]; 8 [size 3]: 8 [size 4]; 5 [size 5]; 4 [size 6] Be sure to choose a range of temperatures (colors) for each star size plotted. Use colored pencils or markers. If you do not have colored pencils, just draw open circles that are the appropriate size as show below. Interpreting the H-R Diagram: Post-Activity Questions [60 pts] These questions appear on an answer sheet on pages 5 and 6. 1. Describe the relationship between color and temperature. How do the colors match up to the temperatures? 2. Describe the relationship between color and size. How do the colors match up to the size of stars? Does this relationship depend on where you look on the H-R diagram (i.e., on or off of the Main Sequence)? Explain. diameter or radius affects its brightness (luminosity). the Main Sequence appears on the H-R diagram. How are stars arranged on the Main Sequence? 3. Describe the relationship between brightness and size (a star's radius or diameter). Explain how changing a star's 4. Can you define an area where most stars are situated? Astronomers call this area the Main Sequence. Describe how 5. What do the stars on the Main Sequence have in common? This property defines a Main Sequence star. 6. All Main Sequence stars are also called stars. [Fill in the blank.] 7. There are three areas off the main sequence where stars seem to group. Identify these three areas as to location relative to the Main Sequence. What kinds of stars are found in each of these three areas?

Explanation / Answer

1.

2. Lower sized stars (1) and bjgger stars like (5, 6) mostly has red to white color range

    Medium sized stars (2 to 4) has a color range from red (lower temperature) to blue (higher temperature)

3. Brightness of the stars increases with increase of star sizes. In technical, the brightness of stars increases    with an increase of radius.

4. Most of the stars are situated from 0 to -5 range in the X - Y plot.

The percentage of stars (in the given list of 90) is distributed as follows.

Magnitude (0-5): 13.33%; Magnitude (5-!0): 13.33%; Magnitude (10-15): 16%

Magnitude (15-20): 6.66%; Magnitude (0-(-5)): 37.77%; Magnitude (-5 to -10):12.22%.

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