TORONTO TIME
THE GNOMON OF THIS SUNDIAL, BEING PARALLEL TO THE EARTH'S AXIS OF ROTATION, POINT TO THE NORTH CELESTIAL POLE. IT'S ANGLE ABOVE THE HORIZONTAL IS THUS 43°40' (THE LATITUDE OF TORONTO). THE SHADOW CAST ON THIS EQUATORIAL SCALE (ROMAN NUMERALS) SHOWS THE APPARENT SOLAR TIME FOR THIS LONGITUDE (79°24' WEST OF GREENWICH), XII (NOON) MARKING THE SUN'S CROSSING OF THE MERIDIAN.
THE NATURE OF THE EARTH'S MOTION CAUSES THE LENGTH OF THE SOLAR DAY TO VARY APPRECIABLY THROUGHOUT THE YEAR. TO YIELD TORONTO MEAN TIME THE SUNDIAL READING MUST BE ADJUSTED ACCORDINGLY. TO CONVERT IT TO EASTERN STANDARD TIME (MEAN TIME FOR THE 75TH MERIDIAN), 17½ MINUTES MORE MUST BE ADDED. THE TOTAL CORRECTION IS TABULATED ON THE SUNDIAL BASEPLATE.
THE SUN'S DECLINATION, ITS ANGULAR DISTANCE NORTH OR SOUTH OF THE CELESTIAL EQUATOR, IS SHOWN BY THE SHADOW OF THE CENTRAL BEAD (USING THE ARABIC NUMERAL SCALE, POSITIVE FOR NORTH). OWING TO THE TILT OF THE EARTH'S AXIS, THE VALUE VARIES UP TO 23½° IN EITHER DIRECTION, IN A SIMPLE ANNUAL CYCLE. THE SUN'S ELEVATION ABOVE THE SOUTHERN HORIZON AS IT CROSSES THE MERIDIAN IS FOUND BY ADDING 46°20' (THE CO-LATITUDE) THE DECLINATION.
THE VARIOUS MONUMENTS IN THIS VICINITY BEAR TESTIMONY
TO THE SCIENTIFIC PIONEERING ACHIEVED IN THE MAGNETIC
AND METEOROLOGICAL OBSERVATORY WHICH STOOD ON THIS SITE
FROM 1840 TO 1908. GRATEFUL ACKNOWLEDGEMENT IS MADE FOR
THE MANY CONTRIBUTIONS FROM INDIVIDUALS AND INSTITUTIONS:
ATMOSPHERIC ENVIROMENT SERVICE
ONTARIO HERITAGE FOUNDATION
ROYAL ASTRONOMICAL SOCIETY OF CANADA
ROYAL SOCIETY OF CANADA
UNIVERSITY OF TORONTO
FABRICATION OF THE SUNDIALK WAS MADE POSSIBLE THROUGH FUNDING BY
THE CLASS OF 4T3
APPLIED SCIENCE AND ENGENERING
UNIVERSITY OF TORONTO
LATITUDE 43 39' 36.6"N - LONGITUDE 79 23' 42.1"W
TO COMMEMORATE THE
FIFTIETH ANNIVERSARY OF ITS GRADUATION
AND THE
CENTENNIAL OF THE BACHELOR OF APPLIED SIENCE DEGREE
1993