You can export your calendars and save the file in the iCalendar .ics format. iCalendar is the standard for calendar data exchange over the Internet, and .ics is the standard format for iCalendar information.
Export is available from your Import/Export Preferences.
To export a calendar:
Go to Preferences>Import/Export
In Export, select the Type as Calendar
From the Source field select the calendar to export. Click OK.
Click Export.
In the dialog that opens, select Save File and select where to save the file. Click OK.
The calendar is saved as an .ics file that can be imported into any calendar application that supports .ics.