Transcript Lighthouse in the Sky - St. Paul Sail and Power Squadron

Sea Time
H1
Junior Navigation
Chapter 3
1
What
timeTimes
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





Determine watch error and rate
Determine zone description (ZD) from longitude
Determine Universal Time (UT) for sights
Convert
 Zone time (ZT) to Universal Time (UT)
 Universal Time (UT) to zone time (ZT)
 One ZT to a second ZT
Draw time diagrams to visualize Lo, UT, ZT
3
Keeping Accurate Time



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
4
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
ZD+7 ZD+6

5
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
6
Watch Error and Rate


Watch error (WE):
 the inaccuracy with respect to correct time
The rate of a timepiece:


Need to know watch error rate


amount timepiece gains or loses per day
so you can calculate accurate time of a sight
To determine watch error rate:
 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
12:00:00
12:00:00
12:00:00
12:00:00
12:00:00
Rate of Change:
WT
12:00:15
12:00:15
12:00:16
12:00:17
12:00:17
12:00:18
12:00:19
WE
+00:15
+00:15
+00:16
+00:17
+00:17
+00:18
+00:19
4sec/7day = +0.6sec/day
8
Time Signals

U.S. Radio Time Signals
 National Institute of Standards and
Technology (NIST)
 WWV at Fort Collins, CO (1-303-499-7111)
 Second
WWVH in Hawaii
WWV(1-900-410-TIME)
WWVH
0-1
1-45
45-52.5
52.5-60
0.8s Minute beep
Standard tone
Voice Announcement
Ticking
Voice Announcement
Ticking
9
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
10
Apparent & Mean Time

Apparent time
 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


St Paul
St Cloud
12:00:00
11-59-40
Mean time Zone Time is 12 – 08 – 58 (EqT)
 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


Civil time, convenient and easy to use:
 On land, determined by law
 daylight saving time
 Pages 262-265, Nautical Almanac
At sea, use Zone Time – divides earth into zones
 each 15º Lo wide
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
Follow the sign to Greenwich
Reverse the sign from Greenwich
165°W
135°W
105°W
75°W
45°W
15°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
15°E
0°
45°E
30°E
75°E
60°E
105°E
135°E
165°E 13
90°E
120°E
150°E
180°E
Time & Arc


The GP of the Mean
sun moves at a
constant rate
 24 hours to go
around the earth =
360°
In one hour, the mean
sun will cover 15° of
longitude
 360°/ 24 hr per day
= 15°per hour






Time
24 hours
1 hour
4 minutes
1 minute
4 seconds
1 second
Arc
3600
150
10
15’
1’
0.25’
14
Visualizing Time

Earth, as seen
from the South
Pole
15
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
M
16
Visualizing Time

Lower branch
of a meridian
is 180º away,
always shown
as broken line
and labeled
“m”
M
m
17
Visualizing Time


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

Lower branch
of Greenwich
meridian is a
broken line
labeled “g”
M
G
g
m
19
Visualizing Time

Sun’s position
plotted as a
solid line and
labeled with
symbol “ ”
M
G
g
m
20
Visualizing Time



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
and
is it’s
at
‘g’ and
ZT 0000
it’s GMT
0000
g
What time is it
atatyour
Greenwich?
position?
ZT 0000
UT
ZT 1800
0600
92º
St Paul – 92º W
of Greenwich
G
m
23
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
24
Sight Reduction Form
Date of Observation
Watch Time
Watch Error
Zone Time
Zone Description
Computed UT
Date at Greenwich
25
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
26
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
 15’ ÷ 60’ = .25°
 114°15´ = 114.25°
 114.25° ÷ 15° = 7.6, rounded to 8
 Since Lo is West, the ZD is positive
 ZD = +8
27
Find ZD
For longitude 79° 30´E, what is the ZD?
Longitude 79° 30´E = 79.50°
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°
172.48° ÷ 15° = 11.49
Since remainder < 0.50, rounded to 11
ZD = +11
28
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.
29
Converting ZT to UT


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?
Lo
is 125°W


ZD is 125 ÷ 15 = 8.33 rounded to 8
Since West Lo, the sign is (+)
 ZD = +8
+ 8
1100
1900
30
Using Time Diagram



Ship is at M, 125°
west of Greenwich (G)
M
Zone meridian is Lo g
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
G
31
m
ZT to UT
Your longitude is 135° E, at ZT 0600, 29 October.
ZD is
÷ 15
= date?
9.0 rounded to 9
What
is 135
the UT
and
 Since this is east longitude, sign is (-)
29 Oct
3000 0600
-
9
2100
28 Oct
32
Using Time Diagram



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
M
g
G
33
m
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
 Since this is west longitude, sign is (+)
4 Jul
2000
+
8
0400 2800
5 Jul
34
Using Time Diagram



Since Lo is West,
place “G” 126.5° east
of “M”
g
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
M ZM
G
35
zm m
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
 Since this is east longitude, sign is (-)
1 Aug
2019
-
9
1119
1 Aug
36
Using Time Diagram


Since Lo is east, place
“G” 128.75° west of
“M”
Draw ZM at 120E,
Position sun 20
hours past “zm”
ZM M
g
G
37
m zm
International Date Line



IDL - mainly follows the 180th 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 Bora)
Chatham Islands,
New Zealand
38
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?
ZT1
1200 6 Nov (before crossing)
ZD1 + 12
UT
2400 6 Nov
ZD2 - 12 (rev)
ZT2
3600
6 Nov
- 24hr + 1day
ZT2 1200
7 Nov (after crossing)
39
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?
ZT1 1200
6 Nov (before crossing)
ZD1 - 12
UT
0000
6 Nov
+ 24 hr - 1 day
UT
2400
5 Nov
ZD2 + 12 (rev)
ZT2
1200
5 Nov (after crossing)
40
Calculate ZT Crossing IDL

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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
ZT1
1200 12 May (1st fix)
ZD1 + 12
UT1
2400 12 May
Travel + 8 hr
UT2
3200 12 May
- 24 hr +1 day
UT2
0800 13 May
ZD2 - 12 (rev)
ZT2
2000
13 May (2nd fix)
42
One ZT to Another
You want
are attoanchor
call your
in Sydney,
wife in St
Australia
Paul (ZD
(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
ZT1
ZD1
UT
1000
+6__
1600
ZD2 - 10 (rev)
ZT2
2600
- 24 hr
ZT2
0200
ZD -10
31 Oct
St Paul
31 Oct
g
Sydney
31 Oct
+1 day
1 Nov
1000
G
m
44
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
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?
a. Lo 27° 43'W ZD ___
+2
-10
b. Lo 154° 38'E ZD ___
Determine ZD:
27°43’W = 27.72°
27.72° ÷ 15° = 1.8
Therefore ZD = +2
ZT
1758 8 Jun
ZD
+2
UT
1958 8 Jun
UT __________
1958, 8 June
0758, 8 June
UT __________
Determine ZD:
154°38’E = 154.63°
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?
a. Lo 156° 14'E ZT _________________
1443, 27 September
0443, 27 September
b. Lo 003° 58'W ZT _________________
Determine ZD:
156°14’E = 156.23°
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°
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