Sundial for Grahamstown

Note that the "squares" on the diagram must look square, ie one unit of length horizontally must equal one unit of length vertically.

The data used to create this sundial are listed below, if you want to make your own large "walk-on" sundial. The columns are:

• Time: time at each marker on the timeline.
• Xtime: X (horizontal) offset from 0.0 (centre of graph) of each time marker.
• Ytime: Y (vertical) offset from 0.0 (centre of graph) of each time marker.
• Date: Date of each marker on the date line and analemma ("8")
• Xan: X (horizontal) offset from 0.0 (centre of graph) of each date marker on the analemma.
• Yan: Y (vertical) offset from 0.0 (centre of graph) of each date marker on the analemma; this is equal to the Y offset for the dateline. The X values for the dateline are 0.0.
• Teqn: The offsets of time correction scale at the foot of the analemma, in minutes. -15 means the Sun is 15 minutes late (e.g. in February), so 15 minutes must be added to the time read from the shadow crossing the timeline when standing on the dateline. +15 means the Sun is 15 minutes early (e.g. in early November), so 15 minutes must be subtracted from the time read from the shadow crossing the timeline when standing on the dateline.
• XTeqn: X (horizontal) offset from 0.0 of the time correction at the foot of the analemma. The Y value is set to place it conveniently below the analemma.

       Grahamstown Area
        Time       Xtime       Ytime        date         Xan         Yan        Teqn       XTeqn
       05h00       2.391      -0.320       Jan01      -0.040       0.890      -15.00      -0.164
       05h30       2.466      -0.181       Jan15      -0.101       0.812      -10.00      -0.109
       06h00       2.498      -0.038       Feb01      -0.149       0.652       -5.00      -0.055
       06h30       2.488       0.105       Feb15      -0.154       0.479        0.00       0.000
       07h00       2.436       0.247       Mar01      -0.135       0.287        5.00       0.055
       07h30       2.342       0.384       Mar15      -0.099       0.088       10.00       0.109
       08h00       2.207       0.515       Apr01      -0.044      -0.157       15.00       0.164
       08h30       2.035       0.636       Apr15      -0.001      -0.351                        
       09h00       1.828       0.747       May01       0.033      -0.556                        
       09h30       1.590       0.846       May15       0.040      -0.708                        
       10h00       1.325       0.929       Jun01       0.025      -0.843                        
       10h30       1.037       0.997       Jun15      -0.004      -0.899                        
       11h00       0.731       1.048       Jul01      -0.039      -0.894                        
       11h30       0.413       1.081       Jul15      -0.065      -0.829                        
       12h00       0.087       1.095       Aug01      -0.067      -0.686                        
       12h30      -0.240       1.091       Aug15      -0.050      -0.519                        
       13h00      -0.562       1.068       Sep01       0.000      -0.312                        
       13h30      -0.876       1.027       Sep15       0.051      -0.120                        
       14h00      -1.174       0.968       Oct01       0.112       0.108                        
       14h30      -1.452       0.892       Oct15       0.154       0.304                        
       15h00      -1.705       0.802       Nov01       0.179       0.530                        
       15h30      -1.929       0.697       Nov15       0.169       0.692                        
       16h00      -2.120       0.581       Dec01       0.119       0.832                        
       16h30      -2.275       0.454       Dec15       0.055       0.897                        
       17h00      -2.391       0.320                  -0.040       0.890                        
       17h30      -2.466       0.181                                                            
       18h00      -2.498       0.038                                                            
       18h30      -2.488      -0.105                                                            
       19h00      -2.436      -0.247