Are the SI units used in astrophysics? Just a curious question, do astrophysicist use the SI units, for example in this equation, 
 
$r = 5pc$, will this be converted to meters?
And what does this $\nu$ stand for? 
 A: Astronomy does not use SI (mks) units1.  CGS (Centimeter-Gram-Second)-Gaussian2 units are the standard in astro fields.  I've yet to hear a good explanation for why cgs is used, but gaussian units can definitely be convenient.
In your above equation, $\nu$ (pronounced: 'nu') is the standard symbol for frequency, and has units of inverse time (1/s).  The standard astronomical procedure would be to use distance ($r$) in cm, planck's constant ($h$) in erg-seconds, and the luminosity in erg/s.

1: Some experimentalists, who are often associated more closely with 'physics' than astronomy or astrophysics, sometimes do use SI (MKS).
2: Gaussian is a sub-unit system of CGS involved in electricity-and-magnetism.  In this system, you can write the electromagnetic force simply as  $F = \frac{q_1 q_2}{r^2}$, without the usual numerical prefactor that you see in SI $\left( \frac{1}{4\pi \epsilon_0} \right)$.
A: Yeah, convert it to meters. Other units are used for quick-and-dirty conceptual stuff, but when it comes to the math, you need to keep your units consistent. 
$\nu$ is frequency. Hence the exchange:
"Hey, what's new?" asked Alan.
"$\nu$ is frequency!" answered Betty.
Alan blinked twice, and began looking for an exit to this conversation.
