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

 search | help desk | commons
 » Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Celestial Navigation Exercise 5.4 #2

Author Topic: Celestial Navigation Exercise 5.4 #2
 Brad posted December 08, 2011 01:26 PM                   I am having a problem with exercise 5.4,#2 in the instructions it tells you to take the (DR-Lon)found in box#1 and bring it down to the (a-Lon-w+e) found in box#3 is this a print error or am I not doing one of the the steps right?In the Answers section found on page 186 in the Starpath Celestial Navigation -A Home Study Course it says "DR-Lon 123 00'W" but when looking at the a-Lon it says "-122"I am new to this all and just want to make sure I'm not forgetting a step.Please help!!!Thanks,Brad From: Los Angeles
 Capt Steve Miller posted December 08, 2011 03:19 PM                   The answer to the first part of your question is NO this not a print error.For the second part of your posting, rather than explaining here I am directing you to page 63 in the textbook where it explains the proceedure on determining the assumed Longitude.If you are having a problem understanding the 5th paragraph under step 4, please post a more detailed question. From: Starpath
 Brad posted December 09, 2011 02:06 AM                   Captain Miller, Thank you for your quick response to my questions. It seems that I am still confused even after reading the explanation found on page 63 paragraph 5 as per your instruction. After looking at all the answers from pages 186. Sun 5.5 to page188 6.5b Sun, all of the (Dr-Lat’s) in degrees are the same as the (a-Lon’s) but this is not the case in the answer found in 5.4 sun#2. Question, Is the reason for this change in the degrees section of the (a-Lat) cause by there being more then 30 minutes apart? Because by looking at the minute section only for both (DR-Lon) and (GHA) it is more as per the example of 37.6 minutes found in Sun 5.4 compared to all the other exercises in this section.I was doing great on all of the previous exercises until hitting this wall....AaaaaaaaughThanks again for your assistanceBrad Summers From: Los Angeles
 Capt Steve Miller posted December 09, 2011 07:16 AM                   To answer your question about the degrees being increased because of the minutes being bigger than 30' is YES. That being said with the minutes being 37.6' you would be 37.6 away from the 122° and 22.4' away from 123°. Hope this clears it up. From: Starpath
 Brad posted December 09, 2011 10:44 PM                   Thanks again for a timely response to my questions, I am still a little hazy at this point and hope my new question will help me in better understanding the procedure.Example: if my (Dr- Lon) was 123º09‘W and I had a (GHA) of 145º 44.4‘, would my answer be (a-lon) 122º 44.4' ?So if this assumption is correct then the rule is always subtract 1º from the (a-Lon) if the minutes are more then 30’ or am I off to be keel hauled.. From: Los Angeles
 Capt Steve Miller posted December 10, 2011 06:48 AM                   Your assumptions are correct. There are times when you go up and when yo go down with the value of degrees it all depends on the final assumed Longitude being less than 30' larger or smaller than your DR Longitude. This whole thing is to make your final answer (the intercept ) to be as small as possible so your accuracy of your resulting Line of Position is as good as you can get it. From: Starpath
 Brad posted December 10, 2011 04:12 PM                   Capt. Miller,I greatly appreciate your time spent on helping me understand the procedures and the quick responses to my questions.I am hoping to have smooth sailing from here, so if I don't run aground on this endeavor I would like to wish you and yours a wonderful holiday season!Brad From: Los Angeles
 bmatteo66 posted May 13, 2020 07:17 AM                   Good Morning Captain.I just did the quizzes of chapter 9. And my REPETITIVE mistake is on determining a-Lon (I'd say especially if "E").I've read the rule at page 63 100 times and still can't figure it out!Here's my process (quiz CN09-0021)DR = 100* 8' EGHA Long = 204* 12' ESo .. minutes of a-Lon = 60-12 = 48' (so far, OK)But ° for a-Lon .. was wrong .. Here's my reasoning ..DR-Lon with a-Lon Minutes = 100* 48'Now I have to chose the ° "withing 30' of DR-Lon with a-Lon Minutes"Because we are EAST, 100* 48' is closer to 99*So now I figure it out for EAST (I think)Let's move to WEST ((quiz CN09-0023)DR = 91* 11' WGHA Long = 91* 38.3' WSo .. minutes of a-Lon = 38.3' (so far, OK)But ° for a-Lon .. was wrong ..DR-Lon with a-Lon Minutes = 91* 38.3'Now I have to chose the ° "withing 30' of DR-Lon with a-Lon Minutes"Because we are WEST, 91* 38.3' is closer to 92*(But the solution is 91*)I need to find a way to figure this out. It sounds so simple, but I can't get it. I need a "Click"!Thank you for your help
 bruce posted May 14, 2020 08:27 PM                   DR = 91* 11' Wminutes of a-Lon = 38.3' DR-Lon with a-Lon Minutes = 91* 38.3'DR-Lon is 91* 11' WIt looks (?) like you're looking for a whole-degree a-Lon within 30' of (DR-Lon with a-Lon minutes)What you want is an a-Lon within 30' of 91* 11' Wa-Lon of 91* 38.3' is within 30' of 91* 11'a-Lon of 92* 38.3' is NOT within 30' of 91* 11'The thing to remember is you're using parts of two different things - -- the minutes part of GHA to get the minutes part of a-Lon, and then-- pick the degrees part of a-Lon so that the whole a-Lon (degrees, minutes) is within 30' of DR_LonBruce From: Everett, WA

 All times are Pacific