Day/Hour Angle Calculation?

Hi there! I am using the DISC excel file from rredc.nrel.gov/solar/models/DISC/ to estimate my DNI using GHI. I am trying to understand the model and is unsure of how the day angle and hour angle are being derived. Can someone enlighten me on this?

Thanks!

Please refer to the documents referenced on that web page, and to the references listed at the end of those documents.

Best regards,
Paul.