Astronomy Principles and Practice Fourth Edition.pdf

The coronagraph 351
By assuming a value of λ = 5 × 10 −4 mm,
d = 5 × 10−4
2(
1
2 062 650 ) mm
≈ 500 mm.
Example 20.3. A Michelson stellar interferometer is used to determine the apparent diameter of a star.
The fringe pattern disappears when the adjustable mirrors are at a separation of 5 m. What is the
angular diameter of the star
By using equation (20.1),
θ = 1·22λ .
d
Again by assuming a value of λ = 5 × 10 −4 mm,
1·22 × 5 × 10−4
θ =
5 × 10 3 rad
= 1·22 × 10 −7 rad
θ ≈ 0·025 arc sec.