1 Homework Q & A Junior Navigation Chapter 9 Meridian Transit of the Sun

2 Objectives: ■ Determine the zone time of meridian transit of the sun by the GHA Method. ■ Make a meridian-transit observation of the sun and compute latitude from the observation

3 Practical Exercise: Problem 1. Follow the Student Manual for guidance

4 2. When the sun crosses your meridian its azimuth is: a.90° or 270° b.45° or 225° c.180° or 360° d.60° or 240° Ref.: ¶ 4

5 3. When the sun crosses your meridian its LHA is: a. 0° b. 90° c. 180° d. 270° Ref.: ¶ 4

6 4. An advantage of using a meridian transit sight to obtain latitude is that this method requires: a. use of a calculator. b. use of tables. c. plotting. d. the maximum altitude of the sun. Ref.: ¶ 4, 15, 17

7 5. The mean sun: a. usually agrees with the apparent sun. b. never agrees with the apparent sun. c. moves in an erratic motion. d. moves in a constant motion. Ref.: ¶ 7

8 6. GHA of the Sun: a. defines the position of the hour circle of the mean sun. b. defines the position of the hour circle of the apparent sun. c. can be converted to mean time by dividing by 15° per hour. d. is measured from the lower branch of the Greenwich meridian to the apparent sun. Ref.: ¶ 9

9 7. Find the ZT of meridian transit for the following dates and Longitudes: a.Lo 175° 46' W on March 29 __________ b. Lo 116° 40' E on June 23 __________ c. Lo 147° 21' W on August 16 __________ d. Lo 128° 36' E on December 5 __________ ZT ZT ZT ZT Ref.: ¶

10 8. The sun's declination on June 21 is approximately: a. 16.7° S b. 23.4° S c. 16.7° N d. 23.4° N Ref.: ¶ 16, Fig. 9-2

11 9. You observe the sun at its maximum altitude, south of your position, and determine Ho is 65° 32', and declination is 20° 10' S. What is your latitude? _______ Solution: Observer is North of Sun Ho = 65°32' Co-Alt = 90° - Ho = 24°28' Co-Alt = 24°28'N Dec = 20° 10'S (Co-Alt & Dec opposite names, subtract) Lat = 04°18'N Ref.: ¶ 18 4° 18'N

On May 7 you observe the sun at its maximum altitude, north of your position, and determine Ho is 62° 41' at a corrected UT time of What is your latitude? ________ 10°16.9'S Solution: Observer is South of Sun Almanac Excerpt (App. B) for 7 May 21 hr Dec 17°01.4'N d(+) 0.7 dcorr + 0.7' Dec 17°02.1'N Ho = 62°41' Co-Alt = 90° - Ho = 90° - 62°41' Co-Alt = 27°19.0'S (since observer south of sun) Dec = 17°02.1'N (Co-Alt & Dec opposite names, subtract) Lat = 10°16.9'S Ref.: ¶ 18

On April 18 you are at approximately L 35°N and Lo 17°E. You take a series of sights on the lower limb of the sun around the time of LAN. Your HE is 10' and the sextant IC is +0.4'. a. What is your best estimate of the time of LAN? __________ b. What is your Lat? ____________ Lat = 35° 04.5' Sight No. ZT hs ° 24.4' ° 27.9' ° 31.3' ° 36.3' ° 38.0' ° 39.1' ° 39.4' ° 39.5' ° 39.2' ° 39.0' ° 38.9' ° 33.9' ° 29.5' ° 24.3' Ref.: ¶ Click to view solution on MT Form Click to view plot of hs vs. ZT

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16 Meridian Transit of the Sun End Of Homework Q & A Junior Navigation Chapter 9