SUNRISE AND SUNSET COMPUTATIONS

How you determine sunrise and sunset depends on the latitude and date(s) with which you enter the tables. If the date and latitude are listed, you simply find where the two intersect and read the time. However, if you enter the table with a latitude and/or date that falls between the latitudes and dates listed, you must interpolate the time.

For a quick walk through, lets use table 6-7-1 and go through a few examples, as follows:

EXAMPLE 1: Find the time of sunrise at 35N on 10 July. First, find 35N along the left edge of the table. Next, read across, horizontally, until you intersect the time beneath 10 July. If your answer is something other than 04:54, you have misused the table.

EXAMPLE 2: Determine sunrise on 10 July at 37N. Note that latitude 37N is not listed in the list of latitudes. Since 37N is not listed, the time of sunrise along 37N is not listed. The time of sunrise has to be interpolated. To interpolate the time of sunrise for 37N, use the sunrise times for the latitudes listed on each side of 37N. That is, find the time of sunrise for 35N and 40N. Since we have already computed the time of sunrise for 35N on 10 July as 04:54, you have only to determine the time of sunrise for 40N. You should come up with a time of 04:40. Now, it is simply a matter of interpolating the time of sunrise. Using the sunrise times for 35N and 40N, setup the information as follows:  

The difference in the time of sunrise between 35N and 40N is 14 minutes, and the difference in degrees of latitude between 35N and 40N is 5 degrees. Since 37N is between 35N and 40N, the time of sunrise at 37N must occur between 04:40 and 04:54. To find the time of sunrise at 37N, set up a ratio of degrees-to-minutes using the differences in degrees, 2 and 5 and the differences in time, 14 minutes and X. The 5 degrees of latitude between 35N and 40N is equal to 14 minutes (04:54 04:40 = 14 minutes). To find the time that equals 2 degrees, use the ratio 5 degrees is to 14 minutes as 2 degrees

Table 6-7-1.-Sample Page of Sunrise/Sunset Data  

This 6-minute period is the difference in time between sunrise at 35N and sunrise at 37N. Add the 6 minutes to the time of sunrise at 35N. This gives you the time of sunrise at 37N (04:40 + :06 = 04:46 LMT).

EXAMPLE 3: Find the time of sunrise at 60N on 24 July. Note that 24 July is not listed in the table. If the date is not listed, you must interpolate the time. To determine sunrise at 60N on 24 July, use the times of sunrise for the dates listed on either side of the 24th; that is, 22 and 25 July.

Again, you must set up a ratio. This time the ratio is one of time versus days. The factors are X (the unknown time between 03:17 and 03:24), :07 (the total time difference between 03:17 and 03:24), 1 (the difference in days between the 24th and 25th), and 3 (the number of days between the 22d and 25th).

There is a 2-minute difference between the time of sunrise on the 24th and the time of sunrise on the 25th of July. Subtract the 2 minutes from the time of sunrise on the 25th. Sunrise occurs at 03:22 LMT on the 24th.

EXAMPLE 4: Find the time of sunrise for a station along 53N on 15 July. Note that neither 53N nor 15 July is listed in the table. This requires interpolation of the time for both the latitude and the date. First, find the sunrise times for 52N and 54N on 13 and 16 July, as follows:  

A quick look at the time difference between 54N and 52N on the 13th and the 16th shows that there is an 11-minute difference on both days. Since 53N falls halfway between 52N and 54N, the time of sunrise at 53N will fall halfway be-tween the time of sunrise for 52N and the time of sunrise for 54N; that is, 03:49:30 on the 13th and 03:53:30 on the 16th. These times equate to one-half of the 11-minute time difference.  

The next step is to interpolate the time between the dates.

Subtract :01 from the time of sunrise on the 16th: 03:54 - :01 = 03:53 LMT. This is the time of sunrise on 15 July.

Learning Objective: Identify the pro-cedures used in converting LMT to LST and UTC.

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing