Angles and Parallax

Question 1

What is the equation for

An object of length, ℓ, at distance, d, subtends an angle of α (Angular Diameter).

Small Angle Approximation

Answer 1

ℓ = αd

α must be in radians. ℓ and d must be same units.

Question 2

What is the equation for

Distance and Parallax

Answer 2

d = r/p

d in parsecs, p in arcseconds, r in AU (Radius of orbit)

Question 3

What is

Proper Motion

Answer 3

• “Fixed” stars observed slow movement
• Measured in milliarcseconds/year (mas/year)
• Symbol is μ
• μ is a vector (RA and Dec)