Astronomical units, light-years and parallax

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Four plan cards, labeled A to D. Which plan would measure a nearby star's parallax, by Esme's reading?

   • Photograph it from two nearby towns on one clear, moonless night
   • Measure how bright it looks
   • Photograph it against far stars, then again six months later
   • Photograph it twice in one night
2. 2.

   “Parallax diagram:” Why can parallax not be used for very distant stars, by Jun's reading?

   • Far stars shift the most, so their images blur
   • Their light is too old to use
   • Their shift is too tiny to measure
   • Earth's orbit is too wide
3. 3.

   Distance (parsecs) = 1 ÷ parallax (arcseconds); smallest parallax 0.001; 1 parsec ≈ 3.26 light-years. A space telescope can measure parallaxes as small as 0.001 arcseconds. About how far away can it reach, by Kira's math?

   • About 1 parsec
   • About 0.001 parsecs
   • About 1,000 light-years
   • About 1,000 parsecs, about 3,260 light-years
4. 4.

   Luz's friend says a light-year is how long a star lives. Which response is best?

   • Agree: it is one year in space
   • Disagree: it is a distance, about 9.46 trillion km
   • Disagree: it is a speed
   • Agree: it is a star's life span
5. 5.

   Milo's cousin says the farthest stars show the biggest parallax. Which response is best?

   • Disagree: each star shows the same parallax shift against the background
   • Agree: a big parallax means a big distance
   • Agree: farther things move more
   • Disagree: nearer stars shift more, since distance = 1 ÷ parallax
6. 6.

   The IAU fixed 1 AU at exactly 149,597,870,700 m. Why fix it exactly, by Noah's reading?

   • Because it equals a light-year
   • So every scientist uses the same fixed value
   • Because Earth's orbit is a perfect circle around the Sun
   • Because it measures one year
7. 7.

   Distance (parsecs) = 1 ÷ parallax; 1 parsec ≈ 3.26 light-years. X: parallax 0.25; Y: 8 light-years. Star X has a parallax of 0.25 arcseconds. Star Y is 8 light-years away. Which is nearer, by Pia's math?

   • They are the same distance
   • X, at 4 light-years
   • Y, at 8 light-years; X is about 13
   • X, since 0.25 is a small number
8. 8.

   Distance (parsecs) = 1 ÷ parallax; 1 parsec ≈ 3.26 light-years; parallax 0.38. A bright star's parallax is 0.38 arcseconds. About how many light-years away is it, by Zee's math?

   • About 1.2 light-years
   • About 8.6 light-years
   • About 0.12 light-years
   • About 2.6 light-years
9. 9.

   1 parsec ≈ 3.26 light-years; distance 10 parsecs. A star is 10 parsecs away. About how long does its light take to reach Ari?

   • About 3.1 years
   • No time; it arrives at once
   • About 10 years
   • About 33 years
10. 10.

    About how many AU make 1 parsec, and why, by Bo's reading?

    • 1 AU, by definition
    • About 206,265 AU, where 1 AU spans 1 arcsecond
    • About 63,241 AU
    • About 3.26 AU