Sea Time H 1 Junior Navigation Chapter 3

Sea Time H 1 Junior Navigation Chapter 3 1

What time. Times is it? Navigational Civil (Standard) Time – kept on land (DST & ST) Local Time – time at our location Watch Time – uncorrected time on your watch (WT) Apparent Time – position of the sun Zone Time – within 15° longitude segments (ZT) Mean Time – arbitrary, based on rotation of earth Universal Time – time at 0° longitude (UT) Sidereal Time – relative to Aries (Navigation)

Learning Objectives n n n Determine watch error and rate Determine zone description (ZD) from longitude Determine Universal Time (UT) for sights Convert n Zone time (ZT) to Universal Time (UT) n Universal Time (UT) to zone time (ZT) n One ZT to a second ZT Draw time diagrams to visualize Lo, UT, ZT 3

Keeping Accurate Time n n n Chronometer – historically, the time reference onboard Recreational navigators - now use good quality quartz watches A watch used for timing sights must have: n a sweep second hand that can be set OR n have a digital display showing seconds 4

Timekeeping at Sea Standard maritime practice: n Chronometer is set to UT n Ship’s daily routine regulated by ZT n When vessel crosses a time-zone boundary, shipboard clocks/watches (but not chronometer) reset to the new zone time; at the first whole-hour after crossing zone boundary 7 00 D+ 6 Captain has discretion on setting ship time 08 Z + 0 90 ZD C 11 S 7. 0 5 n ZD+7 ZD+6 0 0 0 10 5

Fundamentals n n n Accurate time is needed to look up celestial body’s GP in the Nautical Almanac Celestial bodies – tabulated in the Almanac according to UT Error of 1 sec in time leads to an error of 0. 25 nm in LOP 6

Watch Error and Rate n n Watch error (WE): n the inaccuracy with respect to correct time The rate of a timepiece: n n Need to know watch error rate n n amount timepiece gains or loses per day so you can calculate accurate time of a sight To determine watch error rate: n check time against a radio time signal at 24 -hour intervals for at least a week 7

Watch Error and Rate Chronometer Log Date 23 Sept 24 Sept 25 Sept 26 Sept 27 Sept 28 Sept 29 Sept Signal 12: 00: 00 12: 00: 00 12: 00 Rate of Change: WT 12: 00: 15 12: 00: 16 12: 00: 17 12: 00: 18 12: 00: 19 WE +00: 15 +00: 16 +00: 17 +00: 18 +00: 19 4 sec/7 day = +0. 6 sec/day 8

Time Signals n U. S. Radio Time Signals n National Institute of Standards and Technology (NIST) n WWV at Fort Collins, CO (1 -303 -499 -7111) n WWVH in Hawaii (1 -900 -410 -TIME) Second 0 -1 1 -45 45 -52. 5 -60 WWVH 0. 8 s Minute beep Standard tone Voice Announcement Ticking 9

GPS Time n n Check your GPS receiver’s time display with accurate source n “GPS Time” – not identical to UT If GPS time used for sights: n Include in “Remarks” of your Sight Log the results of checking your GPS time 10

Apparent & Mean Time n Apparent time n The time measured directly by observation of the sun Green Bay Wausau Eau Claire 12: 01: 08 12: 00: 44 apparent 12: 00: 20 Sundial indicates time n n St Paul St Cloud 12: 00 11 -59 -40 Mean time Zone Time is 12 – 08 – 58 (Eq. T) n Arbitrary time that averages out irregularities in sun’s apparent motion & creates a constant 24 -hour day UT is Mean Time 11

Civil vs. Zone Time n n Civil time, convenient and easy to use: n On land, determined by law n daylight saving time Pages 262 -265, Nautical Almanac At sea, use Zone Time – divides earth into zones n each 15º Lo wide n 12

Time Zones 12 +11+10 +9 +8 +7 +6 +5 +4 +3 +2 +1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 12 ZM 7. 5º PM C E 7. 5º -12 Follow the sign to Greenwich Reverse the sign from Greenwich 165°W 135°W 105°W 75°W 45°W 180°W 150°W 120°W 90°W 60°W 30°W +12 172. 5ºW ZD 12 180º 172. 5ºE ZD -/+ Reverse the sign from Greenwich 0° 15°E 30°E 45°E 60°E 75°E 105°E 135°E 165°E 13 90°E 120°E 150°E 180°E

Time & Arc n n The GP of the Mean sun moves at a constant rate n 24 hours to go around the earth = 360° In one hour, the mean sun will cover 15° of longitude n 360°/ 24 hr per day = 15°per hour n n n Time 24 hours 1 hour 4 minutes 1 minute 4 seconds 1 second Arc 3600 150 10 15’ 1’ 0. 25’ 14

Visualizing Time n Earth, as seen from the South Pole 15

Visualizing Time n Observer’s meridian is shown at the top and drawn as a solid line, labeled “M” and called Upper Branch of Observer’s Meridian M 16

Visualizing Time n Lower branch of a meridian is 180º away, always shown as broken line and labeled “m” M m 17

Visualizing Time n n Upper branch of Greenwich meridian is a solid line labeled “G” In this example observer is at Lo 60ºW M G m 18

Visualizing Time n Lower branch of Greenwich meridian is a broken line labeled “g” M G g m 19

Visualizing Time n Sun’s position plotted as a solid line and labeled with symbol “ ” M G g m 20

Visualizing Time n n n Sun moves in a counterclockwise (west) direction Sun can be located on diagram for any given time In this example it is 1500 ZT and 1900 UT on the same date M G g m 21

Time Diagram Circle represents the equator M Long tick marks drawn every 15° (hour) Small tick marks placed every 5° (20 minute) Center represents South Pole m 22

Visualizing Time M Your At Greenwich day begins when new day Mean begins Sun is. Mean at ‘m’ Sun andis it’s at ‘g’ and ZT 0000 it’s GMT 0000 g What time is it at your Greenwich? position? ZT 0000 UT ZT 1800 0600 92º St Paul – 92º W of Greenwich UT 0000 G m 23

UT for Sights n Nautical Almanac uses Universal Time n n Remember: UT is Mean Time Need to convert ZT of sight to UT n Apply watch error (WE) to watch time (WT) recorded for sight n If the WE is fast - subtract; if slow - add n Determine ZD of your position n Apply ZD to corrected WT to get UT 24

Sight Reduction Form Date of Observation Watch Time Watch Error Zone Time ram g a i e. D Tim Zone Description Computed UT Date at Greenwich 25

Determining ZD Rule: To Determine ZD n n Divide Lo by 15 Round answer to nearest whole number n Use a plus sign if Lo is west n Use a minus sign if Lo is east 26

How to find ZD n For longitude 114° 15´W, what is the ZD? n To convert minutes of arc to decimal degrees, divide number of arc minutes by 60 n 15’ ÷ 60’ =. 25° n 114° 15´ = 114. 25° n 114. 25° ÷ 15° = 7. 6, rounded to 8 n Since Lo is West, the ZD is positive n ZD = +8 27

Find ZD For longitude 79° 30´E, what is the ZD? Longitude 79° 30´E = 79. 50° ÷ 15° = 5. 3, rounded to 5 ZD = – 5 For longitude 172° 29´ W, what is the ZD? Longitude 172° 29´W = 172. 48° ÷ 15° = 11. 49 Since remainder < 0. 50, rounded to 11 ZD = +11 28

Converting ZT to UT Rule: To obtain UT n Add or subtract the ZD from ZT, using the sign of the ZD. Aid to memory: Follow the sign to Greenwich. 29

Converting ZT to UT n A ship is approaching the entrance to Puget Sound, at 125° W longitude. The ship’s clock shows 1100, Pacific Standard Time. What is UT? n Lo is 125°W n n n ZD is 125 ÷ 15 = 8. 33 rounded to 8 Since West Lo, the sign is (+) n ZD = +8 + 8 1100 1900 30

Using Time Diagram n n M ZD+8 UT Zone meridian is Lo g 120°W, ZT measured from lower branch of this meridian 0 00 11 Sun located 11 hours (165°) west of this lower branch - it is 1100 ZT throughout Zone +8 0 19 ZT n Ship is at M, 125° west of Greenwich (G) G m 31

ZT to UT Your longitude is 135° E, at ZT 0600, 29 October. What is the UT and date? ZD is 135 ÷ 15 = 9. 0 rounded to 9 n Since this is east longitude, sign is (-) 29 Oct 3000 0600 - 9 2100 28 Oct 32

Using Time Diagram n M g 06 00 n Since Lo is East, place “G” 135° west of “M” Since you are on a ZM position sun 6 hours past “m” Since sun has not reached “g” you are one day ahead of Greenwich ZT n G m 33

ZT to UT Your longitude is 126° 30´W at ZT 2000, 4 July. What is the UT and date. ZD is 126. 5 ÷ 15 = 8. 43 rounded to 8 n Since this is west longitude, sign is (+) 4 Jul 2000 + 8 0400 2800 5 Jul 34

Using Time Diagram n 00 M ZM 20 n Since Lo is West, place “G” 126. 5° east of “M” Draw ZM at 120 W, g position sun 20 hours past “zm” Since sun has passed “g” but not reached “m” you are one day behind Greenwich ZT n G zm m 35

ZT to UT Your longitude is 128° 45´E at ZT 2019, 1 Aug. What is the UT and date. ZD is 128. 75 ÷ 15 = 8. 6 rounded to 9 n Since this is east longitude, sign is (-) 1 Aug 2019 - 9 1119 1 Aug 36

Using Time Diagram ZM M g 20 00 n Since Lo is east, place “G” 128. 75° west of “M” Draw ZM at 120 E, Position sun 20 hours past “zm” ZT n G m zm 37

International Date Line n n n IDL - mainly follows the 180 th meridian Add or Subtract a day Why were civil IDL - depends on direction of travel boundaries changed in 1999? Go through Greenwich French Polynesia (including Tahiti & Bora) Chatham Islands, New Zealand 38

IDL Westerly n n n You cross the IDL in a westerly direction at 1200 on 6 November. Before you cross, you are in Zone +12, & after you cross, you will be in Zone -12. What is the ZT and date after you cross the IDL? ZT 1 1200 6 Nov (before crossing) ZD 1 + 12 UT 2400 6 Nov ZD 2 - 12 (rev) ZT 2 3600 6 Nov - 24 hr + 1 day ZT 2 1200 7 Nov (after crossing) 39

IDL Easterly n n n You cross the IDL in a easterly direction at 1200 on 6 November. Before you cross, you are in Zone -12, & after you cross, you will be in Zone +12. What is the ZT and date after you cross the IDL? ZT 1 1200 6 Nov (before crossing) ZD 1 - 12 UT 0000 6 Nov + 24 hr - 1 day UT 2400 5 Nov ZD 2 + 12 (rev) ZT 2 1200 5 Nov (after crossing) 40

Calculate ZT Crossing IDL n n n Enroute to Guam from Honolulu, Hawaii Position fix at 1200 on 12 May 16° 05’N 178° 36’W Traveled westerly for 8 hrs New position fix 14° 42’N 179° 24’E What is ZT & date at your second fix? 41

Calculate ZT Crossing IDL Lo 178° 36’ W ZD = +12 Lo 179° 24’ E ZD = -12 ZT 1 1200 12 May (1 st fix) ZD 1 + 12 UT 1 2400 12 May Travel + 8 hr UT 2 3200 12 May - 24 hr +1 day UT 2 0800 13 May ZD 2 - 12 (rev) ZT 2 2000 13 May (2 nd fix) 42

One ZT to Another You want are attoanchor call your in Sydney, wife in St Australia Paul (ZD +6) -10), at partying 1000, St with Paul your time, Auzzie beforefriends, she leaves on your for work aroundon the-world 31 Oct, to cruise. wish her a happy birthday. When would you initiate your call from Sydney? 43

One ZT to Another 0200 next day M ZT 1 ZD 1 UT 1000 +6__ 1600 ZD 2 - 10 (rev) ZT 2 2600 - 24 hr ZT 2 0200 g ZD -10 31 Oct St Paul 31 Oct Sydney 31 Oct +1 day 1 Nov ZD G m +6 1000 44

Sight Log n n n Data for sights in Sight Folder n Record in Sight Log included in Appendix D Sight Log sheets have columns for WE, ZD, & WT “Remarks” - note anything unusual n If ZT not related to Lo or Standard time n If Daylight Savings Time is applicable 45

Quiz 1. You are at Lo 60° 23'W. Ship's time is kept in ZD 0. If you take a sight at 09 -10 -12 by your watch set to ship's time, what is UT for this sight? a. 05 -10 -12 b. 09 -10 -12 c. 13 -10 -12 d. 09 -10 -12 the next day

Quiz 2. ZT is 1758, 8 June. What are ZD and UT and date if you are at the following positions? +2 a. Lo 27° 43'W ZD ___ -10 b. Lo 154° 38'E ZD ___ Determine ZD: 27° 43’W = 27. 72° ÷ 15° = 1. 8 Therefore ZD = +2 ZT 1758 8 Jun ZD +2 UT 1958 8 Jun 1958, 8 June UT _____ 0758, 8 June UT _____ Determine ZD: 154° 38’E = 154. 63° ÷ 15° = 10. 3 Therefore ZD = -10 ZT 1758 8 Jun ZD -10 UT 0758 8 Jun

Quiz 3. UT is 0443, 27 September. What are ZT and date if you are at the following positions? 1443, 27 September a. Lo 156° 14'E ZT _________ 0443, 27 September b. Lo 003° 58'W ZT _________ Determine ZD: 156° 14’E = 156. 23° ÷ 15° = 10. 4 Therefore ZD = -10 ZT 0443 27 Sep ZD -10 (rev) UT 1443 27 Sep Determine ZD: 3° 58’W = 3. 97° ÷ 15° = 0. 3 Therefore ZD = 0 ZT 0443 27 Sep ZD 0 UT 0443 27 Sep

Quiz 4. One day last June, the sun rose at UT 0958 at Cape Fear, NC, and at UT 1238 at Huntington Beach Calif. If both places are at the same latitude, what is their approximate difference in longitude? Solution: Difference in time of Sun rise is 2 hrs 40 min 2 hours at 15°/hour = 30° +40 minutes at 4 minutes/° = 10° Difference in longitude = 40°

Quiz 5. You have your radio set to receive station WWV. You listen to time ticks for a while and then hear a spoken message: “At the tone, 19 hours zero minutes, Coordinated Universal Time“ At the beginning of a short, high-pitch tone, you notice your watch reads 18 -59 -32. What is your watch error? Watch Error = 28 seconds slow

Sea Time End of Junior Navigation Chapter 3 51