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!     parameters used to define sunrise and sunset (daylength) for different purposes

      real             beamrise
      real             civilrise
      real             nautrise
      real             astrorise

      parameter( beamrise = 90.833 )
      parameter( civilrise = 96.0 )
      parameter( nautrise = 102.0 )
      parameter( astrorise = 108.0 )

!     beamrise   - solar altitude angle at which the upper edge of the sun is visible
!     civilrise  - solar altitude angle defined as civil twilight
!     nautrise   - solar altitude angle defined as nautical twilight
!     astrorise   - solar altitude angle defined as astronomical twilight