The triple-star system α Centauri has a parallax of 0.75 arcsec (the largest parallax known).How far is this star system from the Sun in light-years? (Careful with units!)
A) 4.35 ly
B) 0.41 ly
C) 1.33 ly
D) 0.75 ly

Question

Quizplus · Accepted Answer

The distance (d) in parsecs can be calculated through the inverse relation of the parallax (p) in arcseconds: d=1/p.
Therefore, d=1/0.75=1.333 parsecs. To convert this distance to light-years, we use the definition of a parsec as the distance at which 1 AU (astronomical unit) subtends an angle of 1 arcsecond. 1 parsec = 3.26 ly.
Then, d=1.333 × 3.26 = 4.35 ly. 
So the answer is A).

The Triple-Star System α Centauri Has a Parallax of 0