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?

   • Lower right of the main sequence: a cool red dwarf
   • Top right: a red supergiant
   • A hot star, since red means hot
   • 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 right: a red dwarf, since it is dim
   • On the main sequence beside the Sun
   • Bottom left: a white dwarf, hot but tiny
   • Top left: a blue giant, since it is hot

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 the Sun's size
   • About 10% of the Sun's radius
   • About 100 times the Sun's radius
   • About Earth's size, under 1% of the Sun's radius
6. 4.

   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
   • Agree: the brightest stars are on the right
   • Disagree: dimmer stars are the hotter ones
   • Agree: a star's brightness comes from temperature alone, not its size
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?

   • Disagree: blue stars are the hottest, red the coolest
   • Disagree: a star's color has no link to its temperature
   • Agree: red stars are hottest, like the hot tap
   • Agree: blue means cold
8. 6.

   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?

   • They are the same size
   • The hotter star, since it sits to the right
   • The 4,000 K star
   • The 15,000 K star, since hotter means bigger
9. 7.

   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?

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

    • 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
    • Red dwarfs use fuel the fastest
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 right, then down and left
    • Down along the main sequence, then off the bottom
    • Up and left, then down and right
    • Straight up, then straight down
12. 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
    • Stars spend most of their lives as giants
    • Giants and white dwarfs give off no light