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Introduction    Dial types    Hours (types of)    Time (types of)    Illustration
Symbols    Equations    Biographies    Chronology    Sources    Appendices                                            

U

umbra

: the central, darkest portion of a shadow, i.e. the region which does not receive direct rays from any part of a distributed light source (e.g. the Sun).

umbra recta

Latin for “upright shadow”, it is the label often found on the cotangent scale of altitudes < 45º
on a shadow square.

umbra versa

Latin for “reverse shadow”, it is the label often found on the tangent scale of altitudes > 45º
on a shadow square.

Universal Time (UT

): see time (types of).

Pages: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Introduction    Dial types    Hours (types of)    Time (types of)    Illustration
Symbols    Equations    Biographies    Chronology    Sources    Appendices