1 Sea Time Junior Navigation Chapter 3 H1

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) Navigational Times What time is it?

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

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

5 Timekeeping at Sea Standard maritime practice: Chronometer is set to UT Ship’s daily routine regulated by ZT 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 Captain has discretion on setting ship time Captain has discretion on setting ship time ZD+7ZD+6 C 110 S ZD ZD+6

6 Fundamentals 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 0.25nm in LOP

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

8 Watch Error and Rate Chronometer Log Date 23 Sept 24 Sept 25 Sept 26 Sept 27 Sept 28 Sept 29 Sept WT 12:00:15 12:00:15 12:00:16 12:00:17 12:00:17 12:00:18 12:00:19 Signal 12:00:00 12:00:00 12:00:00 12:00:00 12:00:00 12:00:00 12:00:00 WE +00:15 +00:15 +00:16 +00:17 +00:17 +00:18 +00:19 Rate of Change: 4sec/7day = +0.6sec/day

9 Time Signals U.S. Radio Time Signals U.S. Radio Time Signals National Institute of Standards and Technology (NIST) WWV at Fort Collins, CO ( ) WWVH in Hawaii ( TIME) SecondWWVWWVH s Minute beep 1-45Standard tone Ticking Voice Announcement Voice Announcement Ticking

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

11 Apparent & Mean Time Apparent time Apparent time The The time measured directly by observation of the sun Mean time Arbitrary time that Arbitrary time that averages out irregularities in sun’s apparent motion & creates a constant 24-hour day UT is Mean Time 12:01:08 Green Bay 12:00:44 Wausau 12:00:20 Eau Claire 12:00:00 St Paul St Cloud Sundial indicates apparent time Zone Time is 12 – 08 – 58 (EqT)

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

13 Time Zones 0°0° 15°W 30°W 45°W 60°W 75°W 90°W 105°W 120°W 135°W 150°W 165°W 180°W 15°E 30°E 45°E 60°E 75°E 90°E 105°E 120°E 135°E 150°E 165°E 180°E ZD ºE ºW 180º E C M P ZM 7.5º ZD -/+ Follow the sign to Greenwich Reverse the sign from Greenwich

14 Time & Arc The GP of the Mean sun moves at a constant rate The GP of the Mean sun moves at a constant rate 24 hours to go around the earth = 360 ° 24 hours to go around the earth = 360 ° In one hour, the mean sun will cover 15° of longitude In one hour, the mean sun will cover 15° of longitude 360 ° / hr per day = 15°per hour 360 ° / 24 hr per day = 15°per hour Time Arc Time Arc 24 hours hours hour hour minutes minutes minute 15’ 1 minute 15’ 4 seconds 1’ 4 seconds 1’ 1 second 0.25’ 1 second 0.25’

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

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

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

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

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

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

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

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

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

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

25 Sight Reduction Form Sight Reduction Form Date of Observation Watch Time Watch Error Zone Description Zone Time Computed UT Date at Greenwich Time Diagram

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

27 How to find ZD For longitude 114°15´W, what is the ZD? To convert minutes of arc to decimal degrees, divide number of arc minutes by 60 To convert minutes of arc to decimal degrees, divide number of arc minutes by 60 15’ ÷ 60’ =.25° 15’ ÷ 60’ =.25° 114°15´ = ° 114°15´ = ° ° ÷ 15° = 7.6, rounded to ° ÷ 15° = 7.6, rounded to 8 Since Lo is West, the ZD is positive Since Lo is West, the ZD is positive ZD = +8 ZD = +8

28 Find ZD For longitude 79° 30´E, what is the ZD? For longitude 172° 29´ W, what is the ZD? Longitude 79° 30´E = 79.50° 79.50° ÷ 15° = 5.3, rounded to 5 ZD = –5 Longitude 172° 29´W = ° ° ÷ 15° = Since remainder < 0.50, rounded to 11 ZD = +11

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

30 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? Converting ZT to UT Lo is 125 ° W ZD is 125 ÷ 15 = 8.33 rounded to 8 Since West Lo, the sign is (+) ZD =

31 Using Time Diagram M m Ship is at M, 125° west of Greenwich (G) Ship is at M, 125° west of Greenwich (G) Zone meridian is Lo 120°W, ZT measured from lower branch of this meridian Zone meridian is Lo 120°W, ZT measured from lower branch of this meridian Sun located 11 hours (165°) west of this lower branch - it is 1100 ZT throughout Zone +8 Sun located 11 hours (165°) west of this lower branch - it is 1100 ZT throughout Zone +8 G g ZD+8 UT 1900 ZT 1100

32 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 Since this is east longitude, sign is ( - ) Oct Oct

33 Using Time Diagram M m Since Lo is East, place “G” 135° west of “M” Since Lo is East, place “G” 135° west of “M” Since you are on a ZM position sun 6 hours past “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 Since sun has not reached “g” you are one day ahead of Greenwich G g ZT 0600

34 ZT to UT Your longitude is 126° 30´W at ZT 2000, 4 July. What is the UT and date. ZD is ÷ 15 = 8.43 rounded to 8 Since this is west longitude, sign is (+) Jul 5 Jul 0400

35 Using Time Diagram M m Since Lo is West, place “G” 126.5° east of “M” Since Lo is West, place “G” 126.5° east of “M” Draw ZM at 120W, position sun 20 hours past “zm” Draw ZM at 120W, position sun 20 hours past “zm” Since sun has passed “g” but not reached “m” you are one day behind Greenwich Since sun has passed “g” but not reached “m” you are one day behind Greenwich G g zm ZM ZT 2000

36 ZT to UT Your longitude is 128° 45´E at ZT 2019, 1 Aug. What is the UT and date. ZD is ÷ 15 = 8.6 rounded to 9 Since this is east longitude, sign is (-) Aug

37 Using Time Diagram M m Since Lo is east, place “G” ° west of “M” Since Lo is east, place “G” ° west of “M” Draw ZM at 120E, Position sun 20 hours past “zm” Draw ZM at 120E, Position sun 20 hours past “zm” G g zm ZM ZT 2000

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

39 IDL Westerly 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 Nov (before crossing) ZD UT Nov ZD (rev) ZT Nov - 24hr + 1day ZT Nov (after crossing)

40 IDL Easterly 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 Nov (before crossing) ZD UT Nov + 24 hr - 1 day UT Nov ZD (rev) ZT Nov (after crossing)

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

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

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

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

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

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

Quiz 2. ZT is 1758, 8 June. What are ZD and UT and date if you are at the following positions? a. Lo 27° 43'W ZD ___UT __________ b. Lo 154° 38'E ZD ___UT __________ , 8 June Determine ZD: 27°43’W = 27.72° 27.72° ÷ 15° = 1.8 Therefore ZD = +2 ZT Jun ZD +2 UT Jun Determine ZD: 154°38’E = ° ° ÷ 15° = 10.3 Therefore ZD = -10 ZT Jun ZD -10 UT Jun , 8 June

Quiz 3. UT is 0443, 27 September. What are ZT and date if you are at the following positions? a. Lo 156° 14'E ZT _________________ b. Lo 003° 58'W ZT _________________ 1443, 27 September 0443, 27 September Determine ZD: 156°14’E = ° ° ÷ 15° = 10.4 Therefore ZD = -10 ZT Sep ZD -10 (rev) UT Sep Determine ZD: 3°58’W = 3.97° 3.97° ÷ 15° = 0.3 Therefore ZD = 0 ZT Sep ZD 0 UT 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 What is your watch error? Watch Error = 28 seconds slow

51 Sea Time End of Junior Navigation Chapter 3