Astrophysics 05 - Stellar Distances

How can you use parallax to calculate distance?

Calculate an angle to a fixed point from two locations a known distance apart. The distance from you on average to that fixed point is found by the average the perpendicular distances found using trigonometry.

Give the equation for the distance from the Earth to a star, given a small angle of parallax.

Distance to the star ≈ radius of the earth’s orbit / angle of parallax (radians)

d ≈ r / θ

Give the definition of a parsec, and its length in meters.

A star is exactly one parsec away if the angle of parallax is one arcsecond or (1/3600)°

1pc = 3.08 ×10¹⁶ m

Define a lightyear, and its length in meters and parsecs.

The distance an EM wave can travel in one year through a vacuum.

1 ly = 9.46 ×10¹⁵ m

1 pc = 3.26 ly