NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tom Sult
Date: 2015 Mar 12, 17:27 -0500
Tom Sult, MD
I use it quite a bit.
Maybe an example would help answer your question?
Working with the following date and time;
March 12, 2015
GMT= 20:15:21
First let's determine GHA;
1- Find the year in "table a". Next to 2015 you'll see a +1. That means add 1 hour to the GMT you're working with for the year 2015. In the example's case that means GMT 20 + 1= 21 GMT. Rememember or write down "21".
2- Locate the Month ("Mar") in the big table above table a.
3- Find the day number in the left hand column labled "d" which is headed at "OT 00h". In this example it would be "12".
4- Move across the "12" line to find in the "Mar" "E" column the numbers 2 30 (which means 2° 30')
5- Locate the number just below 2° 30' and find 2 34 (which means 2° 34'). For the use of Table 4 you must use the figure in the next day number to determine what I call the "offset".
6- Notice that the difference between 2 30 and 2 34 is 4 minutes or arc and that the "E" figure is increasing. In this example
I would write down +4.7- Get the GMT number you determined in step 1 above which is 21.
8- Here's how I arrange those numbers; +4/21. You need those numbers for table b.
9- In "table b" locate in the "Diff." column the number 4.
10- In "h" column drop down to find the number 21.
11- Where the 4 column and the 21 (h in bold) intersect you'll see the number 4.
12- Add the 4 to the figure you obtained in step 4 from the "E" column 2 30. The answer is 2 34.
Write figure down. You'll need it later in step 17.13- Now get the real hour and minute figure you're using which is 20:15.
14- In table c locate 20 in the "h" column.
15- Find the 10m column at the top of table c (we'll deal with the remaing 5 minutes and seconds in step 18)
16- Where the 20 and 10 intersect you'll find the number 117 30 which means 117° 30'
17- Add the 117° 30' to 2° 34' to get 120° 04'
18- In table d find 05 in the "m" column and 21 in the "s" column (it's the 4th column from the left side of table d).
19- Next to the 21 in the "s" column you'll see 1 21 slightly down to the right of it in the ° and ' columns.
20- Add the figure you found in step 19 (1° 21') to the figure you determined in step 17 (120° 04') to get 121° 25'.
21- The Sun's GHA for the date and time in this example is 121° 25'.
Declination is done in the same way EXCEPT you go no further than table b.
'Hope that helps.
Sam L.
