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
   • Photograph it twice in one night
   • Measure how bright it looks
   • Photograph it from two nearby towns on one clear, moonless night
2. 2.

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

   • Their shift is too tiny to measure
   • Far stars shift the most, so their images blur
   • Their light is too old to use
   • 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 0.001 parsecs
   • About 1,000 light-years
   • About 1 parsec
   • 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?

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

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

   • Agree: farther things move more
   • Disagree: each star shows the same parallax shift against the background
   • Agree: a big parallax means a big distance
   • 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 Earth's orbit is a perfect circle around the Sun
   • So every scientist uses the same fixed value
   • Because it measures one year
   • Because it equals a light-year

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 9,000 times longer
   • About 9 × 10⁶ times longer
   • About the same; both are about 4
   • About 4 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 2.4 × 10¹² years
    • About 750 years
    • About 4.25 years
    • About 75,000 years
11. 9.

    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 0.12 light-years
    • About 2.6 light-years
    • About 1.2 light-years
    • About 8.6 light-years
12. 10.

    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