# Parallax question.

1. Mar 2, 2009

### MathematicalPhysicist

The question:
A triple stellar system, showing a parallax of 0.01 arcsecond, is composed of a binary system,
with a distance between the two stars of 0.2 AU, and a third star, at a distance of 90 AU from
the binary. This system is observed in the optical (wavelength of 55000 Angstram) with a 1 meter telescope.
a. What is the distance of this system ?
b. How many stars will actually be seen when using a space-based telescope ?
c. How many stars will be seen when using a ground-based telescope, where the typical seeing
is 1 arcsecond ?

My attempt at solution
a. Well, $$\theta=0.01[arcseconds]$$, $$D=\frac{\lambda}{\theta}$$ where lambda is the wavelenghth given in the brackets, and D is the distance of this stellar system from earth.

Don't know how to do b. and c., any advice?