AQA
A Level
A Level Physics
ASTROPHYSICS: Stars 1
(
2022
Total Marks: /30
, 1. The distances to stars are so large that is is convenient to use units other than m.
Total for Question 1: 8
(a) Define, in words, the units AU and ly. [2]
Solution: AU: average distance from the earth to the sun.
ly: the distance travelled by light in a vacuum in one year.
(b) Show that 1 pc=3.1 × 1016 m. One astronomical unit is equivalent to 1.5 × 1011 m. [2]
Solution: 1 pc is the distance at which a radius of 1 AU subtends an angle of 1 arcsecond
(1/3600◦).
AU 1.5×1011
Therefore, by trigonometry: tan(1arcsecond) = pc → 1 pc = 1 )
tan( 3600 = 3.1 × 1016 m
(c) Calculate the distance to a star whose parallax angle measures 0.30 arcseconds. Give your answer [3]
in AU, ly and pc.
Solution: 3.33 pc = 10.9 ly = 689 kAU
A Level
A Level Physics
ASTROPHYSICS: Stars 1
(
2022
Total Marks: /30
, 1. The distances to stars are so large that is is convenient to use units other than m.
Total for Question 1: 8
(a) Define, in words, the units AU and ly. [2]
Solution: AU: average distance from the earth to the sun.
ly: the distance travelled by light in a vacuum in one year.
(b) Show that 1 pc=3.1 × 1016 m. One astronomical unit is equivalent to 1.5 × 1011 m. [2]
Solution: 1 pc is the distance at which a radius of 1 AU subtends an angle of 1 arcsecond
(1/3600◦).
AU 1.5×1011
Therefore, by trigonometry: tan(1arcsecond) = pc → 1 pc = 1 )
tan( 3600 = 3.1 × 1016 m
(c) Calculate the distance to a star whose parallax angle measures 0.30 arcseconds. Give your answer [3]
in AU, ly and pc.
Solution: 3.33 pc = 10.9 ly = 689 kAU
