Astronomical units, light-years and parallax

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

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

   • Their shift is too tiny to measure
   • Their light is too old to use
   • Far stars shift the most, so their images blur
   • Earth's orbit is too wide
2. 2.

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

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

   • Agree: it is a star's life span
   • Agree: it is one year in space
   • Disagree: it is a speed
   • Disagree: it is a distance, about 9.46 trillion km
4. 4.

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

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

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 4 times longer
   • About 9 × 10⁶ times longer
   • About the same; both are about 4
   • About 9,000 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 750 years
    • About 75,000 years
    • About 4.25 years
    • About 2.4 × 10¹² 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 8.6 light-years
    • About 1.2 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 33 years
    • About 10 years
    • About 3.1 years
    • No time; it arrives at once