I recommend downloading the full package (~1.3 GB) and then customizing the install. The easiest way to get LaTeX onto OS X is via MacTex. One new thing that I learned was how to include both EPS and PDF figures in the same document! Read on for step-by-step instructions for installing LaTeX, AASTeX, MN2E, and more. In a future post, I’ll describe how to get TextMate setup as the primary LaTeX editor. In this post, I’ll walk you through the installation and setup that should work for any of the code and text editors that Tom discussed a couple weeks ago (e.g., TextMate, TexShop, Emacs). Over the long US holiday weekend I got LaTeX and all of its bits installed on my new 13″ MacBook Pro (named Gloria).
LaTeX, pronounced “la tech”, is a typesetting program that we use to write our papers (instead of Word or somesuch nonsense).
Update (March 8, 2013): New information on adding directories for package management.