| my account | login-logout | resources | classroom help | support | catalog | home | get webcard |

 search | help desk | commons
 » Online Classroom   »   » Public Discussion of Cel Nav   » Time of Sunset While Running

Author Topic: Time of Sunset While Running
 michael gondro posted November 04, 2004 11:19 AM                   Dec 10 1981,your 1300 ZT DR is LAT 26*27.0 S Long 79*04.0 E course 068T Speed 14kts. What willbe the zone time of sunset at your vessel.
 michael gondro posted November 05, 2004 10:58 AM                   The question number is #1267 and the ansers were1824-1846-1854-1908. I have had some success witha few other questions but need a better way of dealing with the speed and distance traveled during the time it takes for the sun to set or rise. Thank you for the help. Mike
 David Burch posted November 05, 2004 12:38 PM                   This problem is worked in two steps. first find out event time when not moving as a first estimate, then DR from present time to that time to get a better estimate of where you will be at that time, then do the estimate again using the better DR position. In the real world this extra step is rarely called for since we are not often moving fast enough to change the time much, but for a ship at 15 or 20 kts this can shift the time several minutes. First, lets have a look with the StarPilot calculator or software program. We might be off as much as a minute, but not more.Procedure:(1) find zone time of sunset assumed S=0 from DR position. figure ZD as Lon rounded to nearest degree/15 and then round to nearest whole number. ie 79/15=5.2666 ---->5 and in east lon this is -5hSo use settings to set UT offset to -5h, then find sunset at DR position to be 18h 29m 18s.that would be the answer if we were not moving at all. often this will be one of the choices, it was not in this case.(2) between present time of 1300 and time of sunset 1829 we will move 76.84 miles in direction 068. this you can solve by plotting or better by computation. with starpilot go to setting and make DR mode = speed, set DR time to 1300 and enter course and speed... then from main menu do update DR to 18 29 18 to get the new position which is 25° 58.2' S, 80° 23.0' E.(3) now look up the sun set time again from this position and get 18 22 59 which is 1823, so the first answer 1824 must be right.this is off a minute from the answer, but i do not know without working with the actual 1981 almanac data which is correct.we will add some more details on the solutions by hand with paper almanac as soon as we get them scanned from our notes.--david From: Starpath, Seattle, WA
 michael gondro posted November 05, 2004 03:59 PM                   I used the NA arc of time table and the interpolation table in the back of the alminacand got grear results. The only one that gave me ahard time were the ones where the vessels speed and course were east or west. when it was north orsouth the time were right on. mike

 All times are Pacific