1. Module 3 – Naval Skills Chapter 3 – Time and Navigation Section 2 – Kinds of Time Unit 4 - Marine Navigation

2. Demonstrate a basic understanding of navigation and the significant instruments used in this science What You Will Learn To Do

3. 1.Describe the various kinds of time 2.Describe the aspects of the date/time group Objectives

4. CPS Key Term Questions 1 - 13 Key Terms

5. Solar time ‑ Time based on the apparent motion of the Sun around the Earth Key Terms Mean time ‑ Average solar time, based on the Sun’s apparent journey around the Earth (360°) in exactly 24 hours Revolution (of Earth) ‑ Path the Earth takes around the Sun

6. Key Terms Local mean time ‑ The time at your location based on the mean position of the Sun Mean Sun ‑ A hypothetical sun moving at a constant rate equal to the mean speed of the real sun making its annual circuit Universal coordinated time (UTC) ‑ An international time scale based on the frequency of vibrations of the radioactive cesium atom

7. Almanac ‑ An annual publication with a calendar indicating the times of sunrises and sunsets, phases of the moon, tides, and other astronomical statistical information and related topics Key Terms Equation of time ‑ The difference between apparent time and the mean time

8. Standard time ‑ A 15°-wide sector or zone of the Earth in which the same time is kept by all it; uses as a basis the relationship of the mean Sun with the central meridian of the zone Key Terms Zone time ‑ Time reckoned according to the relationship of the mean Sun with the central meridian of each 15° ‑ wide time zone

9. Zone description (ZD) ‑ The difference between the time in a zone and GMT Key Terms Daylight savings time ‑ Time change to gain an extra period of evening daylight; not used in navigation Date/time group (DTG) ‑ A number assigned to a communication that indicates the date and time.

10. (Use CPS “Pick a Student” for this question.) In what ways is timekeeping in the Navy different from timekeeping in civilian life? Opening Question

11. CPS Lesson Questions 1 - 2 Warm Up Questions

12. Kinds of Time The Sun is the most convenient reference for reckoning time.

13.  Apparent time Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time Solar time is time based on the apparent motion of the Sun around the Earth. Apparent time is time based on the apparent position of the Sun from your position.

14.  Apparent time Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time If the Sun is directly over the meridian we are on, we say that it is noon, local apparent time. When it is directly over the meridian 180° away from yours, it is midnight, local apparent time.

15.  Apparent time Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time If the Earth stood still in space, and the Sun orbited in a circle around it, all days reckoned by apparent time would be exactly the same length. Hypothetical perfect orbit of a 24-hour/360° circuit.

16.  Apparent time Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time The Earth’s axis is inclined with respect to the plane of its orbit around the Sun, and the Earth’s speed along its elliptical orbit varies.

17.  Apparent time Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time Therefore, the length of a solar day varies according to the position of the Earth in its orbit.

18. Apparent time  Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time It would be confusing if some days had more hours and others fewer because of the Earth’s revolution, so an average, or mean solar time, is used.

19. Apparent time  Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time Mean solar time is calculated from the motion around the Earth of an imaginary Sun, which always makes the 360°-circuit in exactly 24 hours. Hypothetical perfect orbit of a 24-hour/360° circuit.

20. Apparent time  Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time Local mean time (LMT) is the time at your location based on the mean position of the Sun – that is, at 1200 LMT, the mean Sun is over your meridian, not the actual Sun. Example monthMean sun difference NovemberActual sun ahead 16 1/2 minutes FebruaryActual sun behind 14 minutes

21. Apparent time  Mean time Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time The equation of time is tabulated in publications called nautical almanacs, and must be taken into account for certain tasks in celestial navigation at sea.

22. CPS Lesson Questions 3 - 4 Check On Learning Questions

23. Apparent time Mean time  Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time There is a modern base for time that is more accurate than calculations based on the relationship of Earth and the Sun. It is atomic time or universal coordinated time (UTC).

24. Apparent time Mean time  Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time UTC is an internationally agreed-upon time scale based on the frequency of vibrations of the radioactive cesium atom. Cesium is a fairly common element and readily available for atomic clocks everywhere.

25. Apparent time Mean time  Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time UTC and GMT can differ at certain times by as much as 9/10 of a second. The difference is usually smaller, and can be disregarded for most navigational purposes. UTC Based on the unchanging cesium frequency GMT Based on the relative motion of Earth and the Sun

26. Apparent time Mean time  Atomic/UTC time Zone time Daylight savings Zone time/GMT Kinds of Time Greenwich mean time (GMT) is time based on the relationship of the mean Sun to the prime meridian. Greenwich

27. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Zone time (ZT) = standard time. Standard time zones were established to eliminate short-distance differences if local mean time (LMT) were strictly observed. Observing LMT, a person on the east end of NYC’s 42nd Street would be about 9 seconds off from a person on the west end.

28. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Since one hour is 15°, each time zone is based on a division of the globe into 24 zones of 15° each. A standard time-zone system is fixed by international agreement and by law in each country.

29. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time The zones begin at 0° with the Greenwich meridian. Each meridian is at the center of its time zone, and extends 7 1/2° (half of 15°) on either side of the meridian, but may vary to make life easier for people living there. Greenwich Prime meridian

30. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Each time zone is identified by a letter and by a negative or positive number. The number is called the zone description (ZD), and the letter is called the suffix. West of ZDs +1 to +12 West of 0°, ZDs +1 to +12 -1 -2 -3 -4 -5 -7 -8 -9 - 10 - 11 - 12 East from the prime meridian

31. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time The international date line is at the 180th meridian. The time of day is the same on both sides of the line. However, it is one day later on the west side of the line.

32. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Time zone perimeters fall between longitude lines.

33. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time The result is that the zone descriptions -12 and +12 each extend 7 1/2° (half of 15°) over a longitudinal line, to the international date line.

34. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time The continental United States has four standard time zones.

35. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Eastern standard time (EST) is identified as +5 Romeo (R).

36. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Central standard time (CST) is identified as +6 Sierra (S).

37. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Mountain standard time (MST) is identified as +7 Tango (T).

38. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Pacific standard time (PST) is identified as +8 Uniform (U).

39. Apparent time Mean time Atomic/UTC time  Zone time Daylight savings Zone time/GMT Kinds of Time Alaska is identified as +9 Victor (V). Hawaii is identified as +10 Whiskey (W).

40. Apparent time Mean time Atomic/UTC time Zone time  Daylight savings Zone time/GMT Kinds of Time Daylight savings time (DST) is not used in navigation.

41. Apparent time Mean time Atomic/UTC time Zone time  Daylight savings Zone time/GMT Kinds of Time Daylight savings time is zone time set ahead one hour. The practice varies, but when used, it extends summer evening daylight. For the northern hemisphere: “Spring” forward an hour to begin DST “Fall” back an hour to end DST In the southern hemisphere, summer is December to March, so DST, if used, begins in the latter part of the year.

42. CPS Lesson Questions 5 - 6 Check On Learning Questions

43. Apparent time Mean time Atomic/UTC time Zone time Daylight savings  Zone time/GMT Kinds of Time The Greenwich Mean Time is identified as 0 Zulu (Z). Greenwich meridian 0°

44. Apparent time Mean time Atomic/UTC time Zone time Daylight savings  Zone time/GMT Kinds of Time Most information in navigational tables and naval communications uses GMT, so you must know how to convert the time in any zone to GMT.

45. Apparent time Mean time Atomic/UTC time Zone time Daylight savings  Zone time/GMT Kinds of Time Each time zone represents one hour, beginning at Greenwich. The zone description positive numbers run west and negatives east. West of ZDs +1 to +12 West of 0°, ZDs +1 to +12 -1 -2 -3 -4 -5 -7 -8 -9 - 10 - 11 - 12 East from the prime meridian

46. Kinds of Time Convert from Convert to Algebraic expression Example GMT Any time zone ZT = GMT - ZD From GMT to zone Echo (E) 0600Z - (-5h) = 1100E Any time zone GMTGMT = ZT + ZD From zone Sierra (S) to GMT 0600S + (+6) = 1200Z ABCDEFGHIKLM -1-2-3-4-5-6-7 -8 -9 -10 -11 -12 YXWVUTSRQPON +12+11+10+9+8+7+6 +5 +4 +3 +2 +1 Z0

47. Kinds of Time Note that in algebra, two minuses make a plus. Converting from GMT, subtraction is used. If the ZD is negative, the ZD is added to the GMT time. Convert from Convert to Algebraic expression Example GMT 0600Z Golf time zone ZT = GMT - ZD From GMT to zone Golf (G) 0600Z - (-7h) = 1300G

48. Apparent time Mean time Atomic/UTC time Zone time Daylight savings  Zone time/GMT Kinds of Time The zone time alphabetical suffixes are: Easterly A Alpha B Bravo C Charlie D Delta E Echo F Foxtrot G Golf H Hotel I India K Kilo L Lima M Mike Westerly N November O Oscar P Papa Q Quebec R Romeo S Sierra T Tango U Uniform V Victor W Whiskey X X-ray Y Yankee Greenwich Z Zulu

49. Apparent time Mean time Atomic/UTC time Zone time Daylight savings  Zone time/GMT Kinds of Time In writing naval time, it is generally required to place a time zone’s letter after the numbers. Example: 11: 00 a.m. in Norfolk would be written 1100R

50. Kinds of Time Another aspect of naval time, called the date/time group, involves the date, the month, and the year in naval communications. With a constant (24/7) flow of communications, there must be some way to identify exactly when a message was originated or received.

51. Kinds of Time The date/time group (DTG): Is placed in the message heading Identifies when a communication originated Is used for filing

52. Kinds of Time The DTG consists of six digits. The first two digits represent the date, the second two digits represent the hour, and the third two digits represent the minutes. Example: 151635Z APR 10 means the 15th day of April plus the time in Greenwich mean time (GMT).

53. (Use CPS “Pick a Student” for this question.) Describe the components of a date/time group number. Review Question

54. CPS Lesson Questions 7 - 8 Closing Questions

55. Questions?