Galaxies, the Milky Way and our place in it

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   A galaxy's measured outer star speeds match the speeds predicted from its visible matter alone. What would that suggest, by Esme's reading?

   • More dark matter than usual
   • The galaxy must be elliptical
   • Little dark matter in that galaxy
   • Its stars must be closer than measured

2. Read this first

   Outer star speeds (model data)

   Speed	Value
   measured	200 km/s
   from visible matter	100 km/s

3. 2.

   Outer stars orbit at 200 km/s; visible matter predicts 100 km/s. Needed mass grows with speed squared. About how many times the visible mass is there, by Jun's math?

   • About 2 times
   • About 4 times
   • About 0.25 times
   • About 100 times
4. 3.

   Four evidence cards, labeled A to D. Which observation is evidence for dark matter, by Kira's reading (NASA)?

   • Galaxy clusters bending light more than their visible matter can
   • Black holes at galaxy centers
   • Stars that are too dim to see
   • Dark gaps between the bright stars in a long-exposure space photograph

5. The Milky Way (NASA)

   Fact	Value
   disk width	more than 100,000 light-years
   Sun's distance from center	about 26,000 light-years (sources give 25,000 to 28,000)
   one orbit of the Sun	about 230 to 250 million years (sources differ)
   Andromeda	2.5 million light-years away

6. 4.

   Luz's friend says the Sun is at the center of the Milky Way, since everything seems to circle us. Which response is best?

   • Agree: the Milky Way is our solar system
   • Agree: the stars circle the Sun
   • Disagree: the Sun is outside the galaxy
   • Disagree: the Sun is about halfway out and orbits the center
7. 5.

   Milo's cousin says a light-year is a long time, so a galaxy 2.5 million light-years away is 2.5 million years old. Which response is best?

   • Agree: light-years measure age
   • Agree: the galaxy formed when its light left
   • Disagree: it is a speed
   • Disagree: it is a distance; the light left 2.5 million years ago
8. 6.

   Light from a galaxy 13 billion light-years away shows it as it was when the universe was young. About how old was the universe then, using an age of 13.8 billion years, by Pia's math?

   • About 800 million years old
   • As old as it is today
   • About 13 billion years old
   • About 26.8 billion years old
9. 7.

   How many kilometers is 2.5 million light-years, at about 9.46 trillion km per light-year, by Ren's math?

   • About 3.8 × 10⁶ km
   • About 2.5 million km
   • About 2.4 × 10¹⁹ km
   • About 2.4 × 10¹³ km
10. 8.

    Distance, 2.5 million light-years; speed, 17 km/s, about 0.00006 of light speed. A spacecraft at 17 km/s (about 0.00006 of light speed) heads for Andromeda, 2.5 million light-years away. Roughly how long would the trip take, by Tala's math?

    • About 40 billion years
    • About 150,000 years
    • About 40 years
    • About 2.5 million years
11. 9.

    Two galaxies are found: one smooth and oval with old, red stars, one patchy with bright young blue stars. Which pairing of types fits, by Ari's reading?

    • Irregular, then elliptical
    • Spiral, then elliptical
    • Both are spirals
    • Elliptical, then irregular
12. 10.

    Why will the coming Milky Way–Andromeda meeting not put Earth in danger, by Bo's reading (NASA)?

    • Earth sits at the Milky Way's quiet center, away from the action
    • Stars are so far apart that collisions are very rare
    • The two galaxies are not moving toward each other
    • Dark matter will stop them