# Units for planetary orbits?

1. Aug 8, 2009

### lagwagon555

Hi all, I'm working on a problem where I have to find the time it takes for a planet to form from a protoplanetary disk, using the equation:

$$t = \frac {3}{A}M^{1/3}$$

Where

$$A= ( \frac {(1+2\beta)\sigma}{P}) (\frac {3\pi^2}{4\rho_m})^{2/3}$$

However, I'm not sure which units the periods should be calculated with. Results from google seem to use both, and the units I'm given for in the question are days. However, seconds would seem the logical thing to use. Calculating using both, and choosing the best answer won't really work, since I have no idea how long a sensible answer would be. Any suggestions? Thanks.

Incidentally, does anyone know how to get large brackets around fractions, when using Latex?

2. Aug 9, 2009

3. Aug 9, 2009

### tiny-tim

LaTeX

Hi lagwagon555!
Type "\left(" and "\right)"

(also works with {} [] ||)

Last edited: Aug 9, 2009