Read a Hertzsprung-Russell diagram

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   H-R diagram with the main sequence, giants, supergiants and white dwarfs shaded. NASA's example: a star at about 3,700 K with a brightness of about 0.1. Where does it plot, and what is it, by Esme's reading?

   • Lower left: a white dwarf
   • Lower right of the main sequence: a cool red dwarf
   • A hot star, since red means hot
   • Top right: a red supergiant

2. Read this first

   Model stars (model data; Sun values from IAU)

   Star	Surface temperature (K)	Brightness (Sun = 1)
   A	30,000	10,000
   B	9,900	25
   C (Sun)	5,800	1
   D	3,500	0.01
   E	3,600	100,000
   G	20,000	0.01

3. 2.

   Star G is 20,000 K with a brightness of 0.01. Using radius = √brightness ÷ (T ÷ 5,800)², about how big is it, by Kira's math?

   • About Earth's size, under 1% of the Sun's radius
   • About the Sun's size
   • About 100 times the Sun's radius
   • About 10% of the Sun's radius
4. 3.

   H-R diagram with the giants shaded at the top right. Luz's friend says brighter stars on an H-R diagram are always hotter. Which response is best?

   • Disagree: red giants are cool but bright because they are huge
   • Disagree: dimmer stars are the hotter ones
   • Agree: the brightest stars are on the right
   • Agree: a star's brightness comes from temperature alone, not its size
5. 4.

   Main-sequence band with dots labeled by mass. Milo's cousin says stars move along the main sequence as they age, from blue to red. Which response is best (NASA)?

   • Disagree: mass sets its spot, and it leaves the band when core hydrogen runs out
   • Disagree: stars do not change
   • Agree: blue stars age into yellow, then red ones
   • Agree: the Sun was once a blue main-sequence star
6. 5.

   Two stars both have a brightness of 100. One is 15,000 K and the other 4,000 K. Which is larger, by Pia's reading?

   • The hotter star, since it sits to the right
   • The 15,000 K star, since hotter means bigger
   • The 4,000 K star
   • They are the same size
7. 6.

   Star X has 4 times the Sun's radius and the Sun's temperature. Star Y has half the radius and twice the temperature. Which is brighter (brightness = radius² × temperature⁴), by Ren's math?

   • Y, since it is hotter
   • They are equally bright
   • X, 16 against 4
   • X, 4 against 2
8. 7.

   On the H-R diagram's brightness axis, one star sits 3 gridlines above another. How many times brighter is it, by Tala's math?

   • 3 times
   • 300 times
   • 30 times
   • 1,000 times
9. 8.

   H-R diagram of a cluster: the top left of the main sequence empty, the bottom right full. In a cluster whose stars formed together, the hot blue main-sequence stars are gone but the red dwarfs remain. Why, by Zee's reading (NASA)?

   • Red dwarfs use fuel the fastest
   • Massive blue stars used fuel fastest and left first
   • The blue stars aged into red dwarfs
   • Blue stars are the youngest and have not formed yet
10. 9.

    H-R diagram with the Sun's dot and four path sketches. The Sun will go from the main sequence to a giant, then to a white dwarf. Which path will its dot trace, by Ari's reading?

    • Up and right, then down and left
    • Up and left, then down and right
    • Down along the main sequence, then off the bottom
    • Straight up, then straight down
11. 10.

    Why do most stars we plot fall on the main sequence, by Bo's reading (NASA)?

    • Stars stay on the main sequence for good
    • It is the longest stage of a star's life
    • Giants and white dwarfs give off no light
    • Stars spend most of their lives as giants