Presentation Transcript
Lesson 11c: Celestial Applications: Lesson 11c: Celestial Applications
Lesson 15c: Celestial Applications: AGENDA:
Latitude by Polaris
Gyro Error by Polaris
Gyro Error by Azimuth of the Sun
Computing Times of Sunrise/Sunset Lesson 15c: Celestial Applications
Determination of Latitude: Determination of Latitude As we have already seen, determining position using celestial navigation is a lot of work.
Under certain circumstances, it is possible to determine latitude by using methods which are much less time consuming.
Latitude by Polaris: Latitude by Polaris Polaris (the “pole star”) is so named because it lies almost directly above the north pole (Pn).
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.
Latitude by Polaris: 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.
Determination of Gyro Error: 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.
Determination of Gyro Error: Determination of Gyro Error Gyro Error by Azimuth of the Sun:
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.
Determination of Times of Sunrise and Sunset: 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.
Determination of Times of Sunrise and Sunset: 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/moonset: When the UL of the sun/moon dips below the horizon in its descent.
Determination of Times of Sunrise and Sunset: 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.
Questions?: Questions?
Homework: Homework Read Pages 545-553
Workbook Chapter 16
Section 1: #5
Section 2: #5