1. Lesson 19: Celestial Applications
“Getting Acquainted Lecture”
Instructor Bio:
Commissioned May, 1993; NROTC Unit, IIT
Reported to Hue City (CG-66) homeported in Mayport, FL for a 42 mos tour
24 mos - Engineering Dept (Auxiliaries Officer & Damage Control Assistant)
18 mos - Operations Dept (Air Warfare Officer/BW Flag Liaison Officer)
Command Employment (while aboard Hue City)
1995 Med Deployment 95-2 with USS Theodore Roosevelt
1996 Baltops ‘96 (Scandinavian countries)
1997 Med Deployment 97-2 with USS John F. Kennedy
Midshipmen Cruises (emphasize student contribution to course)
CV (CV 63) - Secrest
Tico’s (LKE, VLG) -Waterston, Pope, Sullivan
Burkes (DDG 61) - Kuckel
OH Perry (FFG 61) - Phillips
LHA/LHD (LSD 44) - Fink, Sutherland
AOE (AOE-8) - Hertel
Review Syllabus:
Course objectives
Course resources (webpage, Textbook, Workbook)
Case studies - provide vivid and intriguing examples of the the fundamental principles taught in this course.
12/29/201812/29/2018

2. Lesson 19: Celestial Applications
AGENDA:
Latitude by Polaris
Gyro Error by Polaris
Gyro Error by Azimuth of the Sun
Computing Times of Sunrise/Sunset
Applicable reading: Hobbs pp pp (skim)

3. Latitude by Polaris
Polaris (the “pole star”) is so named because it lies almost directly above the north pole (Pn).
As a result, the celestial triangle “collapses”.
Co-latitude and co-altitude are one in the same (equal length).

4. Latitude by Polaris
As a result, when in the northern hemisphere, Polaris may be observed, and the altitude of Polaris is equivalent to the observer’s latitude.

5. Latitude by Polaris
In reality, of course, Polaris and the celestial Pn are not exactly coincident; Polaris wanders a bit with respect to the north pole.
To account for this, a correction table is provided in the Nautical Almanac.

6. Determination of Gyro Error
Gyro Error by Polaris
Used in Northern latitudes between the equator and 65 oN.
Observe the true azimuth of Polaris and compare this observed azimuth with the tabulated azimuth of Polaris extracted from the Nautical Almanac.
Advantages/Disadvantages:

7. Determination of Gyro Error
Gyro Error by Azimuth of the Sun:
Similar to the sun amplitude sight, but can be done any time of the day.
The true azimuth of the sun is calculated using a sight reduction form, and compared to the measured value of true azimuth.
Calculations are more involved since a complete sight reduction is required.

8. Determination of Times of Sunrise and Sunset
Important for the navigator.
Determines the time of twilight, both in the morning and evening, when a celestial fix may be obtained.

9. Determination of Times of Sunrise and Sunset
Calculation requires use the Nautical Almanac and the DR plot.
Terms you should be familiar with:
Sun/moonrise: When the UL of the sun/moon first crosses the horizon in its ascent.
Sun/moonrise: When the UL of the sun/moon dips below the horizon in its descent.

10. Determination of Times of Sunrise and Sunset
Terms you should be familiar with:
Civil twilight: UL sun 6o below the horizon.
Nautical twilight: UL sun 12o below the horizon.
The best time to shoot stars is between civil and nautical twilight.

11. Predicting Times of Rising and Setting Phenomena
STEP 1. Obtain the LMT for sunrise/sunset at Greenwich.
STEP 2. In the case of a moving ship, plot DR for this time.
STEP 3. Determine first estimate of sunrise/sunset
a. Find Latitude LMT correction from table I
b. Convert time zone using arc-time difference
c. Plot new DR position
STEP 4. Determine second estimate of sunrise/sunset