The Celestial LOP
Homework
Q&A
Junior Navigation
Chapter 7
1
Objectives:
■ Understand the altitude-intercept method of
plotting and the relationships between Ho,
Hc and intercept.
■ Identify the parts of the navigational
triangle.
■ Compute altitude and azimuth of a celestial
body using a scientific calculator.
■ Convert azimuth angle (Z) to azimuth (Zn)
2
Practical Exercise
1. – 2. Follow the Student Manual for guidance.
3
3. When the observer is closer to the
GP than is the DR:
a. Ho is greater than Hc.
b. Hc is greater than Ho.
c. intercept is away.
d. the radius of the circle of position
through the DR is less than that
through the observer's actual
position.
Ref.: ¶ 16
4
4. In completing a sight reduction of the Sun,
your results indicate Ho = 35°17.4' and
Hc = 35°36.2'.
a. Find the value of the intercept (a).
Ans: 18.8nm
b. Is the intercept (a) toward (T) or away (A)?
Ans: away, since Ho < Hc
c. Are you closer to or further from the GP than
is the DR?
Ans: further from the GP
Ref.: ¶ 14 - 18
Solution:
Hc = 35°36.2'.
Ho = 35°17.4'
a =
18.8' = 18.8nm A
5
5. In completing a sight reduction of the Sun,
your results indicate Ho = 43°45.3' and
Hc = 43°38.8'.
a. Find the value of the intercept (a).
Ans: 6.5nm
b. Is the intercept toward (T) or away (A)?
Ans: toward, since Ho > Hc
c. Are you closer to or further from the GP than
is the DR?
Ans: closer to GP
Solution:
Ref.: ¶ 14 - 18
Hc = 43°38.8'
Ho = 43°45.3'
a=
6.5' = 6.5nm T
6
6. The elevated pole of the navigational
triangle is:
a. the pole having the same name as the
body's declination.
b. the pole having the same name as
the DR latitude.
c. always the North Pole.
d. always the South Pole.
Ref.: ¶ 21
7
7. The distance from the elevated pole
to the reference position or DR is:
a. called co-latitude.
b. called co-altitude.
c. sometimes greater than 90.
d. called latitude.
Ref.: ¶ 24
8
8. Declination is:
a. one side of the navigational triangle.
b. the angular distance from the
observer to the GP of the body.
c. always greater than 90°.
d. the angular distance from the
equator to the GP of the body.
Ref.: ¶ 25, Fig. 7 – 5a
9
9. In the navigational triangle, the
distance from the DR to the GP of the
body is:
a. 90° - Dec.
b. measured along a parallel of latitude.
c. the radius of a celestial circle of
position.
d. measured along a meridian of
longitude.
Ref.: ¶ 26
10
10. Azimuth (Zn) is:
a. always an internal angle of the
navigational triangle.
b. always measured clockwise from true
north.
c. measured from either pole,
depending on the hemisphere in
which the observer is located.
d. always less than 90°.
Ref.: ¶ 28
11
11. If the observer is in the southern
hemisphere and the LHA of the sun
is less than 180:
a. Z is north and east.
b. Z is south and east.
c. Z is south and west.
d. Z is north and west.
Ref.: ¶ Figure 7-6c, Table 7-1
12
12. If the observer is in the northern
hemisphere and the sun is west of
the observer:
a. Zn = 360° - Z.
b. Zn = 180° + Z.
c. Zn = 180° - Z.
d. Zn = Z.
Ref.: ¶ Figure 7-6a, Table 7-2
13
13. The two sides and angle used to
solve the navigational triangle are:
a. declination, azimuth angle, and
altitude.
b. co-latitude, co-altitude, and LHA.
c. co-declination, co-altitude, and
azimuth angle.
d. co-latitude, co-declination, and LHA.
Ref.: ¶ 21 – 29, Figure 7 -6
14
14. Using the values given below, obtain the intercept (a)
and azimuth (Zn) by calculator solution.
a.
b.
c.
d.
DR L
23°19.6'S
14°19.5'N
28°36.4'N
9°56.5'S
DR Lo
87°14.2'W
152°49.8'E
70°50.4'W
89°18.5'E
GHA
43°56.1'
265°53.6'
110°08.5'
232°44.8'
Dec
13°17.2'N
14°26.8'S
15°58.5'N
12°40.5'S
Ho
34°04.3'
24°59.7'
51°48.3'
52°28.5'
Summary:
Note: Solutions use values for LHA, Lat, Dec, and Hc rounded
Click to
Button
5 decimal
places Hc
and entered into
the calculator Zn
as such. Values
To View
LHA
Intercept
of arc sin and arc cos are left in the calculator at full precision
a. and
316°41.9'
34°00.8'
T
054°
Solution a.
converted directly
to Hc and3.5nm
Z.
b.
58°43.4'
25°10.5'
10.8nm A
246°
Solution b.
c.
39°18.1'
51°42.7'
5.6nm T
259°
Solution c.
d. 322°03.3'
52°43.4'
14.9nm A
098°
Solution d.
Ref.: ¶ 48
15
15. Refer to Chapter 6, Homework #6a & #6b. Complete
the bottom portions of the USPS SR96 Form you started
in those exercises to find the intercept (a) and azimuth
(Zn) for those sights by the Law of Cosines method.
For reference, the DR position given in those exercises and
the answers you calculated for LHA, Dec, and Ho
are provided below:
DR L
a. 30°06.8'N
DR Lo
85°43.6'W
LHA
51°12.8'
Dec
10°50.8'N
Ho
38°46.3'
b. 41°18.0'N
73°06.8'W
323°31.7'
7°00.8'S
31°18.2'
Summary:
a. Hc = 38°48.0'
a = 1.7nm A
Zn = 259°
Click to View Solution 15 a.
b. Hc = 31°16.0'
a = 2.2nm T
Zn = 136°
Click to View Solution 15 b.
Ref.: ¶ 48
20
Q7
The Celestial LOP
End Of
Homework Q & A
Junior Navigation
Chapter 7
23