Plotting Celestial LOPs
Junior Navigation
Chapters 8 & 9
and part of Chapter 13
090
270
180
THE OUTER SCALE IS READ FROM A
MERIDIAN OF LONGITUDE. THE
INNER SCALE FROM A PARALLEL
OF LATITUDE.
360
000
180
180
000
1
Learning Objectives

Set up a Constant Latitude Scale Small Area
Plotting Sheet (CLS SAPS)

Plot a single celestial LOP

Plot a celestial running fix

Meridian Transit of the sun

Setup a Universal Plotting Sheet (UPS) – Chap 13
2
Plotting Techniques

Errors result - working too fast - not checking plots





Don’t rush
Sharp-pointed pencil (medium/hard)
Complete plot before labeling
Erase unnecessary lines
Recheck results if they differ by more than 0.5´
on CLS Sheets. Small variations are normal
Constant Latitude Scale Small Area
Plotting Sheet



Directions from
Compass Rose
Latitude Scale fixed,
you select Mid-Lat
You create the Lo
scale for your area
using arcs on lower
part of form
1º
9’
8’
7’
6’
5’
4’
3’
2’
1’
Constant Latitude Scale Small Area
Plotting Sheet
30’



Plot 1258 DR at:
 L 44º 50.6’ N
 Lo 92º 21.2’ W
STEP 1
Label ‘Mid Lat’ that
will allow plot to be
near center of form.
Label each of the
10’ increments.
30’
20’
10’
45ºN
50’
40’
30’
Constant Latitude Scale Small Area
Plotting Sheet
30’



Plot 1258 DR at:
 L 44º 50.6’ N
 Lo 92º 21.2’ W
STEP 2
Lo varies to Mid-Lat
Draw diagonal lines
between the bottom
center & preprinted
values for selected
Mid-Lat
30’
20’
10’
45ºN
50’
40’
30’
Constant Latitude Scale Small Area
Plotting Sheet
30’

000
20’
180
1º latitude
10’
45ºN
000
180
270
090
60nm x 60nm
You are on your way
in becoming a
cartographer
50’
40’
50’
40’
30’
20’
THE OUTER SCALE IS READ FROM A
MERIDIAN OF LONGITUDE. THE
INNER SCALE FROM A PARALLEL
OF LATITUDE.

STEP 3
Intersections of
diagonal lines and
solid arcs mark
locations of 10’
meridians
Draw meridians
Label meridians
1º longitude
180

Plot 1258 DR at:
 L 44º 50.6’ N
 Lo 92º 21.2’ W
360

30’
10’
30’
92ºW
50’
Constant Latitude Scale Small Area
Plotting Sheet
30’
Plot 1258 DR at:
 L 44º 50.6’ N
 Lo 92º 21.2’ W
000
090
270
000
270
360
090
45ºN
000
50’
40’
THE OUTER SCALE IS READ FROM A
MERIDIAN OF LONGITUDE. THE
INNER SCALE FROM A PARALLEL
OF LATITUDE.
180
180
10’
180

000
180
180
THE OUTER SCALE IS READ FROM A
MERIDIAN OF LONGITUDE. THE
INNER SCALE FROM A PARALLEL
OF LATITUDE.
STEP 4
Plot your position
20’
180
360

30’
50’
40’
30’
30’
20’
10’
92ºW
50’
Constant Latitude Scale Small Area
Plotting Sheet
30’


Plot 1258 DR at:
 L 44º 50.6’ N
 Lo 92º 21.2’ W
30’
20’
10’
STEP 5
With sun intercept
4.0nm towards and
azimuth 205º, plot
your estimated
position
45ºN
50’
40’
30’
EP L 44º 47.0’ N
Lo 092º 24.5’ W
50’
40’
30’
20’
10’
92ºW
50’
Constant Latitude Scale Small Area
Plotting Sheet
30’

Sight reduced from
FIX:
 Not an EP, do not
draw a square
 Sight Error (SErr)
intersection of
LOP and azimuth
30’
20’
10’
45ºN
1258
GPS
50’
40’
30’
EP LS Err44º
4.0nm
47.0’ N
Lo 092º 24.5’ W
50’
40’
30’
20’
10’
92ºW
50’
Celestial Fixes


Celestial fix - sights on two/more different
bodies taken within a short time
 Time interval within 20 minutes - a “Fix”
 Time interval longer - a “Running Fix”
Offshore navigators rely on Sun RFix
 Morning LOP advanced to midday
 Midday LOP advanced to evening
 Evening LOP advanced to next morning
11
Plotting a Celestial R Fix
Advancing a LOP using
a construction line that parallels the DR track
30’
30’
0800 @ 0.9nm T 245º
1200 @ 0.8nm A 332º
20’
20’
10’
10’
45ºN
6nm @ 200
45ºN
1200 RFix
18nm @ 260
50’
50’
40’
40’
30’
30’
Plotting a Celestial R Fix
Advancing a LOP using
direction and distance between DR’s.
30’
0800 @ 0.9nm T 245º
1200 @ 0.8nm A 332º
30’
20’
20’
10’
10’
45ºN
45ºN
1200 RFix
50’
50’
40’
40’
30’
30’
Plotting a Celestial R Fix
Advancing a LOP using
the original intercept and azimuth
30’
0800 @ 0.9nm T 245º
1200 @ 0.8nm A 332º
30’
20’
20’
10’
10’
45ºN
45ºN
1200 RFix
50’
50’
40’
40’
30’
30’
Sight Folder Plotting
30’
0858
Sun
20’
10’
1245
RFix
45ºN
0858-1245
GPS
50’
40’
30’
S Err 3.6nm
10’
93ºW
50’
40’
30’
20’
10’
Sight Folder Plotting
30’
0858-1245
Sun
0858
Sun
Changing position
where sights taken.
1245
RFix
10’
1245
GPS
0858
GPS
Resulting RFix must
still be within 5.0nm
of later sight.
20’
45ºN
50’
40’
30’
S Err 4.0nm
10’
93ºW
50’
40’
30’
20’
10’
Universal Plotting Sheets


Offshore: plotting & labeling of courses &
bearings – referenced to TRUE
 Universal plotting sheets used in any part of
the ocean except Polar Regions
 Likely to cross several lines of variation
offshore.
Using True, apply Var & Dev for each leg to
determine Compass course to steer.
17
Universal Plotting Sheets


The UPS covers about
4° of latitude and 4° of longitude
Draw meridian through marks on
Compass Rose at desired mid-latitude
18
Setup for mid-latitude of 37° N and
mid-longitude of 68° W
180
7
360
090
270
180
000
Will be used for chapter 13
homework cruise
180
000

THE OUTER SCALE IS READ FROM A
MERIDIAN OF LONGITUDE. THE
INNER SCALE FROM A PARALLEL
OF LATITUDE.
Universal Plotting Sheets
7
19
Universal Plotting Sheets

70º
69º
68ºW
67º
66º
Setup for mid-latitude of 37° N and
mid-longitude of 68° W
39º
38º
37ºN

Set dividers to the spacing between
central meridian and the one drawn
36º


Measure off and draw remaining
meridians
Label
35º
20
Universal Plotting Sheets
70º

69º
68ºW
67º
66º
Distance & latitude -measured along
Latitude scale on central meridian
39º
38º
37ºN
35º


Longitude - measured
on pre-printed scale
draw line across at
value of mid-lat
36º
37º
38º
39º
36º
35º
21
Longitude Measurements


Measure 15’ of Longitude at
37° Latitude.
Precision on UPS – 1.0nm or
1’ of Latitude/Longitude.
10’ + 5’
22
Universal Plotting Sheets
70º


69º
15º W
Var
68ºW
67º
(ZD+5) (ZD+4)
66º
39º
Plot the 15º W isogonic
line using points:
L1 39º 00’38º
N,
Lo1 69º 20’ W and
L2 35º 00’ N,
ZDLoon
2 66º 45’ W…
Time Zone Boundaries
 Vertical dashed line, with
both
sides
YOU
WILL
USE THIS UPS FOR PLOTTING THE 37ºN
CHAPTER 13 HOMEWORK CRUISE
Isogonic
Lines
 Lines of equal magnetic variation
 Dashed line, with variation shown 36º
15º W
Var
35º
23
Universal Plotting Sheets
15º W
Var
70º
69º
69º
30’
15º W
Var
67º
68ºW
30’
(ZD+5)(ZD+5)
(ZD+4)(ZD+4)
66º
67º
39º
38º
38º
30’
25
20
15
10
DOUBLING THE SCALE
5
37ºN
36º
30’
15º W
Var
15º W
Var
35º
36º
24
Meridian Transit





Celestial body crosses upper branch of observer’s
meridian – body reaches maximum altitude
Meridian Transit of Sun
LHA is 000°
also known as
Body due north/south
Local Apparent Noon (LAN)
Azimuth 360º or 180º
Pn
Observer
Nav. triangle collapses to
Greenwich
straight line - elevated
pole, observer, & GP of
body - all on same great
Equator
GP
Sun
circle:
the observer’s meridian
25
Finding Time of Transit
Mean time of transit is
calculated
26
Finding Time of Transit
Find ZT of MT on 14 Nov
at Lo 092° 21.2´W
Step 1

Record the DR Lo
092 21.2
14

Step 2
Find whole hour GHA
from daily page of
Nautical Almanac,
closest to, but still
smaller than DR Lo
27
Finding Time of Transit
Find ZT of MT on 14 Nov
at Lo 092° 21.2´W
Step 3

Record GHA

Step 4
Subtract whole hour
GHA from DR Lo

Step 5
Browse increments /
corrections pages
18
092 21.2
092 10.9
0 10.3
28
Finding Time of Transit
Find ZT of MT on 14 Nov
at Lo 092° 21.2´W



Step 6
Record increment
Step 7
Add to GHA whole
hour
Step 5
Correct for ZD
18
+
092 21.2
092 10.9
0 10.3
00 41
18 00 41
6
12 00 41
ZD: 21.2’ / 60 = 0.3533
092.3533º / 15 = 6.15
29
Computing Latitude
The Ultimate Backup




Determine Lat w/o calculator, tables, or plotting
Simple and easy to teach to crew members
Quick check of GPS latitude
However, limited availability
 Only once a day, at a specific time
30
Computing Latitude




Correct WT and hs of
the sight at maximum
altitude
Subtract Ho from 90°
to obtain Co-Alt
For UT of the sight,
obtain Dec of sun
from Almanac
Combine Co-Alt and
Dec to obtain your
latitude
 L = Dec + Co-Alt
31
Computing Latitude
Observer North of Sun
50°N
70
20
10
30
Observer
CoAlt
Sun
Equator
50°S
32
Computing Latitude
Observer South of Sun
50°N
30
60
20
40
Sun
Equator
CoAlt
Observer
50°S
33
Taking the Noon Sight

Begin taking sights 10 to 20 minutes before
ZT of MT



Take observations every minute or two
Note altitude and time
 Rate of altitude increase slows as sun
approaches meridian transit
 Near transit, altitude may appear nearly
constant for a few minutes
Helpful to plot run of sights
34
Latitude from MT Sight



DR position on 20 April:
 L 48° 54.0´ N
 Lo 125° 26.0´ W
From a series of sights
around noon, you
selected the maximum
observed altitude
 hs of sun (LL) is
52° 28.9´ at
12–18–26.
WE 2s slow.
HE 10.2 feet, IC +1.2´
What’s your
azimuth angle?
20 Apr 2012
12-18-26
02
+
12-18-28
+ 8
20-18-28
20 Apr
2
48 54 0
125 26 0
Co-Alt

20 11 45 9
+ 09
+
03
11 46 2
125 25 0
120 17 8
20
5 07 2
20 29
20-20-29
8
+
12-20-29
You
Sun
10 2
52 28 9
12
31
12 31
– 1 9
52 27 0
+ 15 2
52 42 2
52
37
11
49
48
42
17
46
04
54
10
2
8
2
0
0
0
35
Meridian Transit of the Sun
End of
Junior Navigation
Chapter 9
Bring your Pilot Chart next week
and
Begin Preparing Sight Folders
36