CHANGE IN SOLAR ELEVATION DURING OBSERVATIONS

The elevation of the sun is constantly changing - even while you are making your daily observations.

The following data is developed to determine how much time you will have to make and mark down your elevation observations before a significant error might be introduced by this change.

The data is for San Francisco at mid-day on the winter solstice on December 22, 2006.

Note that in this example the maximum elevation of the sun does not occur at noon, but at 12:08:30.

Time of Day

Elevation From Solar Calculator

Interpolation From Graph of Solar Calculator Data

 

 Degrees

Degrees

Minutes

12:00 Noon

28.79

 

 

12:01

28.79

 

 

12;02

28.80

 

 

12:03

28.81

 28

 48.3

12:04

28.81

28 

48.6 

12:05

28.81

28 

48.9 

12:06

28.82

28

49.2

12:07

28.82

28

49.3

12:08

28.82

28

49.35

12:08:30

Max Height

28

49.4

12:09

28.82

28

49.35

12:10

28.82

28

49.3

12:11

28.82

28

49.2

12:12

28.81

 28

48.9 

12:13

28.81

28 

48.6 

12:14

28.81

28 

48.3 

12:15

28.80

 

 

12:16

28.79

 

 

12:17

28.79

 

 

12>18

28.78

 

 

12:19

28.77

 

 

12:20

28.76

 

 

If the accuracy of your observations is 1/45th of the diameter of the sun (= 0.67 minutes) then the elevation change in several minutes will be less than your observational accuracy. Thus, you will have a couple of minutes in which to make and record your daily observation.

NOTE: Your available time will be less if your shadow is not from true south, and is always much less when not near the solstice, since the elevation change per day is greater.