Pear Rust - Gymnosporangium sabinae

The aecial stage is on Pear (Pyrus).  Small spermogonia pustules appear on leaf surfaces in Spring, followed by aecia on leaf undersides.  These are swollen galls, bearing large orange-brown aecia which open to release spores through longitudinal slits.  These remain as skeletons after the spores are shed.   There are corresponding bright orange-red blotches on the leaf uppersides. 

The primary telial host is Juniper, on swellings on branches.  The telia are conical, and yellow-brown when wet. 

on Pear

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments

alternates between Juniper and Pear