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

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

   • Their light is too old to use
   • Earth's orbit is too wide
   • Their shift is too tiny to measure
   • Far stars shift the most, so their images blur
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 1,000 light-years
   • About 1 parsec
   • About 0.001 parsecs
   • About 1,000 parsecs, about 3,260 light-years
4. 4.

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

   • Agree: a big parallax means a big distance
   • Agree: farther things move more
   • Disagree: nearer stars shift more, since distance = 1 ÷ parallax
   • Disagree: each star shows the same parallax shift against the background
5. 5.

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

   • Because it measures one year
   • Because it equals a light-year
   • Because Earth's orbit is a perfect circle around the Sun
   • So every scientist uses the same fixed value
6. 6.

   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?

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

7. Read this first

   Light travel times

   Trip	Time
   Sun to Neptune	about 4.2 hours
   Sun to Proxima Centauri	about 4.25 years

8. 7.

   Sunlight takes about 4.2 hours to reach Neptune and about 4.25 years to reach Proxima Centauri. About how many times longer is the trip to Proxima, by Ren's math?

   • About the same; both are about 4
   • About 4 times longer
   • About 9,000 times longer
   • About 9 × 10⁶ times longer

9. Trip to Proxima Centauri

   Quantity	Value
   distance	4.02 × 10¹³ km
   speed	17 km/s
   one year	3.16 × 10⁷ s

10. 8.

    A spacecraft at 17 km/s heads for Proxima Centauri, 4.02 × 10¹³ km away. About how many years would it take (1 year ≈ 3.16 × 10⁷ s), by Tala's math?

    • About 4.25 years
    • About 750 years
    • About 75,000 years
    • About 2.4 × 10¹² years
11. 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
    • About 33 years
    • No time; it arrives at once
    • About 10 years
12. 10.

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

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