Can you add an event from another module using PHP?

Is there an interface/api to add an event to the calendar from another Joomla module?
If not, are the tables such that an event can be added simply?

unfortunately there is no specific api to add events.
But you may just add new row in {prefix}events_rec table.
Here is a list of required fields for single events:
event_id | start_date | end_date | text | user