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3. Time Zones, Zone Description, Chronometer Time

3. Time Zones, Zone Description, Chronometer Time. Presented By: Mate O. 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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3. Time Zones, Zone Description, Chronometer Time

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  1. 3. Time Zones, Zone Description, Chronometer Time Presented By: Mate O

  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. 060°W 045°W 030°W 1100 ZT 1200 ZT 1300 ZT Time and Longitude III: Time In Navigation • If the Sun Is Directly Overhead of an Observer Then 1 Hour Later the Sun Would Be 15° West of the Observer (Because the Earth Has Rotated) • Therefore, Places to the East Have Later Times Than the Observer and Places to the West Have Earlier Times • The Difference in Time Between Two Places Is Equal to the Difference in Longitude Between Their Meridians, Expressed in Units of Time Instead of Arc

  4. The Date Line III: Time In Navigation The Date Line Coincides With the 180th Meridian or the Lower Branch of the Greenwich Meridian. (12 Hours Earlier Then the Time at the Greenwich Meridian). When the Sun Is Over the 180th Meridian the Day Begins (0000 Hours) for the Greenwich Meridian Because the Two Time Zones on Either Side of the 180th Meridian Are 24 Hours Apart, Crossing This Line Will Alter Your Date One Day When Solving Celestial Problems That Involve Crossing the 180th Meridian We Convert Local Time to Greenwich Time and Then Convert Back to New Local Time on the Other Side of the Meridian

  5. Zone Time III: Time In Navigation • At Sea, and Ashore Watches and Clocks Are Normally Set to Zone Time. Everywhere in That Zone Keeps the Same Time • The Center of the Zone Is the Meridian Which Is Exactly Divisible by 15°. It Is Commonly Referred to As the Zone Meridian, Standard Meridian or Central Meridian • Thus a Time Zone Is 7 ½ Degrees on Either Side of a Central Meridian, and Times in Consecutive Zones Differ by Exactly One Hour. • Time Zones Are Numbered From the Greenwich Meridian by How Many Times They Are Divisible by 15° and Given a Positive Sign If They Are West of Greenwich and Negative Sign If East of Greenwich. These Numbers and Signs Are Called Zone Descriptions Standard Meridians Dividing Meridians ZD+2 ZD+1 ZD 0 ZD - 1 ZD – 2 030° W 015° W 015° E 030° E 037 ½ ° W 022 ½ ° W 007 ½ ° W 007 ½ ° E 022 ½ ° E 037 ½ ° E Greenwich Meridian

  6. Zone Time

  7. Converting ZT to GMT III: Time In Navigation • The Zone Description When Applied to Zone Time Will Give You Greenwich Mean Time Example:Your ZT Is 0636 – 15s, Your Zone Description is ZD – 4, What Is the GMT? Solution: ZT 0636 – 15s ZD - 4 GMT 0236 – 15s • The Zone Description When Applied to GMT Must Be Reversed to Give You Zone Time Example: The GMT Time Is 1542 – 36s, Your Zone Description Is ZD + 4, What Is Your Zone Time? Solution: GMT 1542 – 36s ZD - 4 (rev) ZT 1142 – 36s

  8. Converting ZT to GMT III: Time In Navigation Example:The GMT is 1721 – 15s Required: (1) The Zone Time at 156° 24.4’ W (2) The Zone Time at 039° 04.8’ E Solution #1: GMT 1721 – 15s ZD - 10 (Rev +10) ZT 0721 – 15s Solution #2: GMT 1721 – 15s ZD - 3 (Rev -3) ZT 2021 – 15s

  9. III: Time In Navigation Chronometer Time • A Chronometer Is a Timepiece, Which Is Set to GMT Initially, But Over Time It Will Not Always Read Exact GMT. The Difference Between Chronometer Time and GMT Is Known As Chronometer Error. • What Makes a Chronometer an Accurate Time Piece Is That Its Error Can Be Recorded From Day to Day and a Chronometer Error Rate of Change Each Day Can Be Determined. • Knowing the Chronometer Rate One Can Determine What Exact GMT Should Be for Any Given Time on Any Given Day Based Upon the Last Known Error and the Amount of Change That Should Have Occurred in the Period Since the Last Known Error Was Checked. • Chronometer Error Is Recorded As Fast or Slow and to the Nearest Whole or Half Second. Chronometer Rate Is Recorded As Gaining or Losing and Recorded to the Nearest 0.1 Second for Each Day (24 Hours)

  10. III: Time In Navigation Chronometer Time Example: At GMT 1200 on May 12th the Chronometer Read 12h 04m 21s. At GMT 1600 on May 18th It Reads 04h 04m 25s. Solve: 1. Chronometer Error at 1200 GMT on May 12th 2. Chronometer Error at 1600 GMT on May 18th 3. Chronometer Rate 4. Chronometer Error at 0530 GMT on May 27th

  11. III: Time In Navigation Chronometer Time Solution: 1. GMT 1200–00s May 12th 2. GMT 1600-00s May 18th C 1204-21sC 0404-25s Answer CE 4m-21s Fast CE 4m-25s Fast 3. GMT 18d 16h 4. GMT 27d 05h 30m GMT 12d 12hGMT 18d 16h 00m Diff. 6d 4h = (6.2days) Diff. 8d 13h 30m = (8.6 days) CE Fast 4m 21s (1200 12th) CE Fast 4m 25s 1600 May 18th CE Fast 4m 25s (1600 18th)Corr. (+) 0m 05s (8.6x.6) Diff. 4s gained Answer Daily Rate .6s gain (4sec./6.2days) CE Fast 4m 30s 0530 May 27th

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