CEH will optionally allow you to specify that you want to observe Star Parties. This function is very useful for Astonomers and Astonomy Clubs who want to publish calendars for their members or friends indicating when to get together for a night of viewing the stars.
CEH defines a Star Party as the closes Saturday evening to the New Moon. Since New Moon dates can fall on any day of the week, choosing the closest Saturday night is pretty easy to do. The only problem comes when a New Moon falls on a Wednesday. In this case CEH is configured to bias itself toward an earlier setting Moon rather than a late rising Moon. This gives you a more continuous night of viewing.
Sometimes a New Moon will fall within the the first few days of the month. When this happens the closest Saturday night may be the preceeding month. CEH takes this into account in calculating the proper Star Party date.
The cost is $5.00 (US) to add this option.