Read a Hertzsprung-Russell diagram

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Use this

   H-R diagram with the main sequence, giants, supergiants and white dwarfs shaded.

2. 1.

   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?

   • A hot star, since red means hot
   • Lower right of the main sequence: a cool red dwarf
   • Top right: a red supergiant
   • Lower left: a white dwarf
3. 2.

   A star is 25,000 K with a brightness of 0.05. Where does it plot, and why, by Jun's reading?

   • Bottom left: a white dwarf, hot but tiny
   • Bottom right: a red dwarf, since it is dim
   • Top left: a blue giant, since it is hot
   • On the main sequence beside the Sun

4. 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

5. 3.

   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 10% of the Sun's radius
   • About 100 times the Sun's radius
   • About the Sun's size
6. 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: stars do not change
   • Agree: the Sun was once a blue main-sequence star
   • Agree: blue stars age into yellow, then red ones
   • Disagree: mass sets its spot, and it leaves the band when core hydrogen runs out
7. 5.

   Row of star dots from blue on the left to red on the right. Noah's friend says blue stars must be cool, like the blue cold circle on a sink. Which response is best?

   • Agree: blue means cold
   • Disagree: a star's color has no link to its temperature
   • Agree: red stars are hottest, like the hot tap
   • Disagree: blue stars are the hottest, red the coolest
8. 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?

   • X, 16 against 4
   • Y, since it is hotter
   • They are equally bright
   • X, 4 against 2
9. 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?

   • 300 times
   • 3 times
   • 1,000 times
   • 30 times
10. 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)?

    • The blue stars aged into red dwarfs
    • Massive blue stars used fuel fastest and left first
    • Red dwarfs use fuel the fastest
    • Blue stars are the youngest and have not formed yet
11. 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 left, then down and right
    • Up and right, then down and left
    • Straight up, then straight down
    • Down along the main sequence, then off the bottom
12. 10.

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

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