A number of journals, such as Astrophysical Journal and Astronomical Journal, have a particular "style" which authors must follow. You can achieve this easily if you adopt the AASTeX macro package. See the links at the end of this page for the websites at which you can find AASTeX and its documentation.
The simplest way to write a paper using this macro package is to start with a sample document which is already properly formatted, and gradually to replace the sample text --- and figures and tables --- with your own text -- and figures and tables. Fortunately, the AAS provides just such a sample file for you to use inside the download-able AASTeX package.