Galaxies, the Milky Way and our place in it

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   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

2. 1.

   The Sun is about 26,000 light-years from the center (sources give 25,000 to 28,000). About what fraction of the disk's radius is that, if the radius is about 50,000 light-years, by Esme's math?

   • About half
   • About one-tenth
   • About twice the radius
   • Zero, since the Sun is at the center
3. 2.

   The Sun's orbit around the center is about 2π × 26,000 ≈ 163,000 light-years long. At one orbit per about 230 to 250 million years, roughly how fast is it, by Jun's math?

   • About 200 km per hour
   • About 200 km/s
   • Zero, since the Sun sits at the center
   • About 0.0007 km/s

4. Spiral galaxy speeds (model data)

   Distance from center	Measured speed	Speed from visible matter
   10,000 light-years	220 km/s	210 km/s
   30,000 light-years	220 km/s	150 km/s
   60,000 light-years	220 km/s	100 km/s

5. 3.

   Measured star speeds in a spiral galaxy stay near 220 km/s far from the center, but visible matter predicts they should fall. What does this suggest, by Kira's reading?

   • There is extra unseen mass holding the outer stars
   • The outer stars are about to fly away from the galaxy soon
   • The speeds were measured in the wrong units
   • The galaxy is made of dark dust
6. 4.

   In the same table, by how much does the measured speed beat the visible-matter speed at 60,000 light-years, by Luz's math?

   • By 320 km/s
   • By 10 km/s, as at the center
   • By 120 km/s
   • By 0 km/s; they match
7. 5.

   Vera Rubin studied stars at the outer edges of spiral galaxies in the 1970s (NASA). What did Rubin find, by Milo's reading?

   • Outer stars moved slower than expected
   • The galaxies had no outer stars
   • Spiral galaxies are really ellipticals
   • Outer stars moved too fast for the visible matter alone
8. 6.

   Why can't we photograph the whole Milky Way from outside, by Noah's reading (NASA)?

   • It is smaller than the solar system
   • We sit at its center
   • We are inside it, seeing the disk edge-on
   • It is an elliptical with no disk
9. 7.

   The Milky Way appears as a band of light across the night sky. What is that band, by Pia's reading (NASA)?

   • The edge of the solar system
   • The center of the universe
   • A cloud in Earth's air
   • Our galaxy's disk, seen edge-on from inside
10. 8.

    The two galaxies drawing together over billions of years. NASA says the Milky Way and Andromeda will meet in about 4 billion years. What does NASA say will happen to Earth, by Ren's reading?

    • It will happen within our lifetimes
    • Earth will be hit by Andromeda's stars
    • The Sun will move to the galaxy's exact center
    • The solar system is in no danger; the Sun may shift its place
11. 9.

    Sketch of a galaxy with a central bar and two main arms. Which galaxy type does NASA say the Milky Way is, by Tala's reading?

    • A ring of planets
    • An irregular
    • An elliptical
    • A barred spiral
12. 10.

    Pie chart of 30 nearby large galaxies with slices unlabeled. NASA says elliptical galaxies are less common than spirals. In a sample of 30 large galaxies, which count is most likely, by Ari's reading?

    • More spirals than ellipticals
    • More ellipticals than spirals
    • Each of the 30 is irregular
    • Equal numbers of each type