Visual Binary

These stars are in orbit about each other and can be seen both directly.

In the case of a visual binary, direct measurement of R, the linear separation is not feasible. Instead, the angular separation θ can be observed in the sky. If the distance to the binary system d, then R can be calculated:

\[R[AU]=d[AU]\theta [radian]\]

The values of θ are so small that radians are an inconvenient quantity

\[R[AU]=d[pc]\theta [“]\]

but, \(d[pc]=\frac {1}{p[“]}\)so:

\[R[AU]=\frac {\theta[“]}{p[“]}\]