Source: Extra Practice
A parallax of 1 arc second is subtended by an object at a distance of 1 parsec. How many astronomical units (AU) make up 1 parsec?
Options
Option A is correct
2.06 × 10⁵ AU
Option B
1.496 × 10¹¹ AU
Option C
3.08 × 10¹⁶ AU
Option D
1.5 × 10⁸ AU
Explanation
1 parsec is defined as the distance at which an arc of 1 AU length subtends an angle of 1 arc second. θ = l / r => 1" = 1 AU / 1 parsec. Since 1" = (1/3600) * (π/180) radians, 1 parsec = 1 AU / radians value ≈ 206265 AU. 3.08 × 10¹⁶ is the value in meters, not AU. 1.496 × 10¹¹ is the value of 1 AU in meters.