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1 Altitude Corrections Homework Q & A Junior Navigation Chapter 4.

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Presentation on theme: "1 Altitude Corrections Homework Q & A Junior Navigation Chapter 4."— Presentation transcript:

1 1 Altitude Corrections Homework Q & A Junior Navigation Chapter 4

2 2 Objectives: ■ Understand how the following factors affect altitude observations: dip, refraction, parallax, semidiameter. ■ Apply altitude corrections from the Nautical Almanac to observations of the sun.

3 3 Practical Exercises: Problems 1. & 2. Follow the Student Manual for guidance

4 4 3. The correction for dip: a. may be either positive or negative. b. decreases in magnitude as height of eye increases. c. is always negative and increases in magnitude as height of eye increases. d. is always positive and decreases in magnitude as height of eye increases. Ref: ¶ 5

5 5 4. If an observer is taking sights from a pier in an area with a 10- foot tidal range, will his height of eye for computing altitude corrections change over a period of time? Yes. What if the observer is on a boat anchored in the same area? No. Ref: ¶ 5

6 6 5. Which of the following is used as the entering argument to enter altitude correction tables? a. Sextant altitude (hs). b. Apparent altitude (ha). c. Observed altitude (Ho). Ref: ¶

7 7 6. Using the Excerpts from the Almanac, find the observed altitude (Ho) for the following: Date Body hs IC HE Ho a. 27 February Sun LL 28°15.8' +7.3' 8.0ft b. 17 August Sun UL 21°58.2' +0.7' 68.0ft 28°34.9' 21° 32.7' Solution: a. Sun LL, 22 Jan hs 28°15.8' IC +7.3' Dip -2.7' ha 28°20.4 ' Main +14.5' Ho 28°34.9 ' Solution: b. Sun LL, 17 Aug hs 21°58.2' IC +0.7' Dip -8.0' ha 21°50.9 ' Main -18.2' Ho 21°32.7' Ref: ¶

8 8 7. Which of the following corrections needs to be applied in order to determine apparent altitude? a. dip and parallax b. refraction and parallax c. index error and semi-diameter d. dip and index error Ref: ¶ 20, 26

9 9 8. Which of the following corrections are applied to apparent altitude for a sun sight? a. main correction only b. main correction plus semi-diameter correction c main correction plus additional correction d. main correction, additional correction, and HP Ref: ¶ 21, 27

10 10 9. Two JN students take sights on the sun at approximately the same time from approximately the same location at sea. Mary has a HE of 8 feet and an IC of + 1.0'. Jane has a HE of 22 feet and an IC of -2.1'. Assuming both are accurate sights, which of the following is true? a. Jane's sight will have a larger ha than Mary's sight. b. Mary's sight will have a larger ha than Jane's sight. c. Jane's sight will have an hs smaller than Mary's sight. d. The ha for both sights will be about the same. Ref: ¶ 5,

11 11 Altitude Corrections End of Homework Q & A Junior Navigation Chapter 4


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