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14. Sunrise, Sunset, Twilight, Star - Time

14. Sunrise, Sunset, Twilight, Star - Time. Presented By: Kelly Curtin, Asst. Professor. Course Outline. Navigational Astronomy Lecture 1 & 2 Mean Time / Apparent Time Lecture 3 Time Zones, Zone Description, Chronometer Time Lecture 4

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14. Sunrise, Sunset, Twilight, Star - Time

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  1. 14. Sunrise, Sunset, Twilight, Star - Time Presented By: Kelly Curtin, Asst. Professor

  2. Course Outline • Navigational Astronomy Lecture 1 & 2 • Mean Time / Apparent Time Lecture 3 • Time Zones, Zone Description, Chronometer Time Lecture 4 • The Earth, Celestial, And Horizon Coordinate System Lecture 5 & 6 • The Spherical Triangle Lecture 7 • Circle of Equal Altitude Intercept Lecture 8 • Time Diagram, Right Ascension Lecture 9 • The Nautical Almanac, Finding GHA, LHA, and Dec. Lecture 10 & 11 • Instruments For Celestial Navigation Lecture 12 • Sight Reduction of the Sun, Stars, Planets, Moon Lecture 13 - 15 • Plotting and Advancing / Retarding the Assumed Position Lecture 16 • Calculating Time of Meridian Passage (LAN) Lecture 17 • Calculating Latitude at Meridian Passage Lecture 18 • Calculating Time of Sunrise/ Sunset/ Twilight Lecture 19 • Star Shooting Schedule / Pub. 249 Lecture 20 • Azimuth and Amplitudes Lecture 21 – 24 • Polaris – Azimuth and Latitude By Lecture 25 • Star – Finder – Stars, Planets, Selecting the 3 best Stars Lecture 26 • The Complete Day’s Work Lecture 27 & 28

  3. Limits of the Three Twilights XIV: Sunrise, Sunset, Twilight

  4. Pn 0° 6° 12° 18° Sunset Civil Twilight Ps Astronomical Twilight Nautical Twilight XIV: Sunrise, Sunset, Twilight Twilights Sun

  5. Limits of the Three Twilights XIV: Sunrise, Sunset, Twilight Calculating Sunrise, Twilight, and Star Time: The Times Listed In the Nautical Almanac are Correct for the Latitudes Listed at the Central Meridian Time Of Sunrise Time Of Civil Twilight Time Of Nautical Twilight

  6. Limits of the Three Twilights XIV: Sunrise, Sunset, Twilight Calculating Sunset, Twilight, and Star Time: The Times Listed In the Nautical Almanac are Correct for the Latitudes Listed at the Central Meridian Time Of Nautical Twilight Time Of Civil Twilight Time Of Sunset

  7. Limits of the Three Twilights XIV: Sunrise, Sunset, Twilight Symbols Used The Sun Never Sets at this Latitude on This Date The Sun Sets but does not get lower than 6° below the horizon, so it is twilight all night long. The Sun Sets but does not get lower than 12° below the horizon, so it is twilight all night long.

  8. Calculating Sunrise, Star Time XIV: Sunrise, Sunset, Twilight • Calculating Sunrise, Sunset, and Twilight: • To Calculate Sunrise, Sunset, Twilight, Or Star Time We Must First Find The Approximate Time That The Phenomenon Will Occur For Us So That We Can Obtain A DR Position. • This Is Known As An Estimate Of Dr Time (Ball Park) • For Sunset Or Sunrise – Interpolate Between The Times Of S/R Or S/S Which Surround Your Latitude • For Star Time – Interpolate Between The Times Of Civil Twilight Which Surround Your Latitude

  9. XIV: Sunrise, Sunset, Twilight Calculating Sunset, Star Time • Example: On March 23, 1981 Your 1600 DR Pos’n Is Lat. 27° 16.3’ N, λ 156° 48.2’ W. You Are On Course 063° T At A Speed Of 18 Knots. What Will Be The Time Of Sunset, And What Will Be The Time Of Star Time? • Step #1. Estimate of DR Time • Knowing our Latitude Lies Between 20° and 30° we can go into the Almanac and find the times which surround our latitude and interpolate for the time at our latitude and then apply 6° 48’ worth of Arc to the Time. • Since we are calculating Star Time, we will interpolate the civil column. • 30°N 1838 Set up ratio: 10° = 7°16.3 • 4m x • 27° 16.3’N 1837 • 20°N (BASE VALUE) 1834 x=2.9=3min 1834+3= 1837 • So 1837, should be the Time With Which We find our DR Position • 1837 DR Pos’n L 27° 37.7’N • λ 156° 00.9’W

  10. XIV: Sunrise, Sunset, Twilight Calculating Sunset, Star Time • Example: On March 23, 1981 Your 1600 DR Pos’n Is Lat. 27° 16.3’ N, λ 156° 48.2’ W. You Are On Course 063° T At A Speed Of 18 Knots. What Will Be The Time Of Sunset, And What Will Be The Time Of Star Time? • Step #1. Estimate of DR Time • Step #2. Using our DR Time and Position from Step #1 We Can Now Interpolate for Sunset, and Star Time • LAT Sunset Civil Nautical 30°N 1814 1838 1906 27° 37.7’ 20°N 1812 1834 1900 • Our DR Latitude is referenced from the lower tabular latitude in this case 20°. We are 7° 37.7’ away. The tabular interval is the difference between 20° and 30° =10° • We then find the time difference between the times of Sunset, Civil, and Nautical Times = 2, 4, 6 minutes respectively. 10° 2 4 6 7° 37.7

  11. XIV: Sunrise, Sunset, Twilight Calculating Sunset, Star Time • Example: On March 23, 1981 Your 1600 DR Pos’n Is Lat. 27° 16.3’ N, λ 156° 48.2’ W. You Are On Course 063° T At A Speed Of 18 Knots. What Will Be The Time Of Sunset, And What Will Be The Time Of Star Time? • Step #1. Estimate of DR Time • Step #2. Using our DR Time and Position from Step #1 We Can Now Interpolate for Sunset, and Star Time • Step #3 Using The Interpolation Table We Can Correct the times for our Latitude. • LAT Sunset Civil Nautical 30° 1814 1838 1906 27° 37.7 20° 1812 1834 1900 Correct for Lat. 1814 1837 1904 10° +2 2 +3 4 +4 6 7° 37.7

  12. Calculating Sunset, Star Time XIV: Sunrise, Sunset, Twilight • Example: On March 23, 1981 Your 1600 DR Pos’n Is Lat. 27° 16.3’ N, Λ 156° 48.2’ W. You Are On Course 063° T At A Speed Of 18 Knots. What Will Be The Time Of Sunset, And What Will Be The Time Of Star Time? • Step #1. Estimate Of DR Time • Step #2. Using Our DR Time And Position From Step #1 We Can Now Interpolate For Sunset, And Star Time • Step #3 Using The Interpolation Table We Can Correct The Times For Our Latitude. • Step #4 Correct For Longitude By Converting Dr λ Into Arc Adding If You Are West Long. And Subtracting If You Are East. • LAT Sunset Civil Nautical 30° 1814 1838 1906 27° 37.7 20° 1812 1834 1900 Correct for Lat. 1814 1837 1904 Dlo Arc to Time λ 156° 00.9’W from 150°W - 6°00.9’ W of C.M. (add time of 24 minutes Zone Time 1838 1901 1928 These Times are correct for the Phenomenon at the DR Lat. And Long. 2 4 6 10° +4 7° 37.7 +2 +3

  13. Calculating Sunset, Star Time 1850 1915 Star Time XIV: Sunrise, Sunset, Twilight • Example: On March 23, 1981 Your 1600 DR Pos’n Is Lat. 27° 16.3’ N, λ 156° 48.2’ W. You Are On Course 063° T At A Speed Of 18 Knots. What Will Be The Time Of Sunset, And What Will Be The Time Of Star Time? • Step #5 Star Time Is Considered Halfway Between The Time Of Sunset And Civil And Halfway Between Civil And Nautical • LAT Sunset Civil Nautical 1838 1901 1928

  14. XIV: Sunrise, Sunset, Twilight Calculating Sunset, Star Time Note: If only the time of the individual phenomenon is required then only that column needs to be interpolated.

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