time and navigation

CHAPTER 3

TIME AND NAVIGATION

Jet Lag

Temporary disruptions of the body’s

normal biological rhythms after

high-speed air travel through several

time zones

Jet Lag

Time is based on

the relationship

of Earth and the

Sun.

Ship’s Clock

Key For Winding

Gimbal Ring

Gimbal Lock

Ship’s

Chronometer

in its case

A timepiece or timing device with a

special mechanism for ensuring and

adjusting its accuracy, for use in

determining longitude at sea or for

any purpose where very exact

measurement of time is required

Chronometer

• Once started, it is

never allowed to

stop.

• A record is kept

of whether it is

running fast

or slow.

• Time checks are

made against

radio time signals.

Chronometer

Radio stations in Washington, D.C.,

and Honolulu, Hawaii, broadcast time

signals every 5 minutes, 24 hours a

day.

Radio station announcement might be:

―When the tone returns, the time will

be 8:50 a.m. Eastern Standard Time;

8:50 a.m.‖

The ship’s chronometer is then checked

against the time signal by the quartermaster.

Any error is recorded, and the navigator

must take it into consideration when finding

position.

p.m. Post

Meridiem

a.m. Ante

Meridiem,

or before the

middle of the

day (noon)

24–Hour Clock

Why does the military use a 24–hour

clock?

MARINES

AIR FORCENAVY

ARMY

All military services use the 24–hour

clock.

Why does the military use a 24–hour

clock?

• To avoid the confusion that would result if ―a.m.‖ or ―p.m.‖ were left out of a message

• To be consistent with military time in Europe

The day begins a fraction of a second after

midnight, 0000 and continues past 0100 to

noon, 1200. The afternoon continues with 1300

to 2400 (midnight).

While 0000 and 2400 are the same time, it is

common practice to start each day at 0001 and

end it at 2400.

As a cadet, you should memorize the

24–hour clock so it becomes second

nature when telling time.

What time would it be on the 24–hour

clock for the following times?

A. 7:00 a.m.

B. 12:30 p.m.

C. 6:50 p.m.

D. 9:15 p.m.

E. 12:01 a.m.

What time would it be on the 24–hour

clock for the following times?

A. 7:00 a.m.

B. 12:30 p.m.

C. 6:50 p.m.

D. 9:15 p.m.

E. 12:01 a.m.

0700

1230

1850

2115

0001

• Bells are rung every

half-hour.

• One bell is struck for

the first half hour, and

one bell is added for

each half hour up to

eight bells.

• After eight bells (four

hours), the sequence

begins again.

Ship’s Bell Time

• An odd number of

bells marks a half-hour.

• An even number of

bells marks an hour.

Ship’s Bell Time

Bells are rung only from reveille to taps,but not during divine services or whenfog requires that the bell be used as afog signal.

* Not normally sounded

Morning Watch

Time Bells Time Bells

* 0430 1 0630 5

* 0500 2 0700 6

* 0530 3 0730 7

0600 4 0800 8

Forenoon Watch


0830 1 1030 5

0900 2 1100 6

0930 3 1130 7

1000 4 1200 8

Afternoon Watch


1230 1 1430 5

1300 2 1500 6

1330 3 1530 7

1400 4 1600 8

Dog Watch or First Watch


1630 1 1830 5

1700 2 1900 6

1730 3 1930 7

1800 4 2000 8

1600 — 1800 First dog watch1800 — 2000 Second dog watch

The first and second dog watches straddle the time when the evening meal is traditionally served. Those with the first dog eat the evening meal after being relieved and those with the second dog eat before assuming the watch.

Dog Watches

Evening Watch


2030 1

2100 2

2130 3

2200 4

* Bells are not sounded after taps

How many bells would be struck

at the following times?

A. 0600

B. 0930

C. 1600

D. 1830

E. 2000

How many bells would be struck

at the following times?

A. 0600

B. 0930

C. 1600

D. 1830

E. 2000

4 bells

3 bells

8 bells

5 bells

8 bells

Time is reckoned according to the

travel of the Sun once around the

Earth each day.

In the sixteenth

century, the

astronomer

Copernicus

established

that the Earth’s

Rotation makes

the Sun seem to

move.

The Earth rotates 360° in 24 hours.

(360° ÷ 24 hours = 15° per Hour)

In 1 hour, the Earth rotates 15°.

1° longitude = 4 minutes of time

Therefore...

60 minutes (1 hr) ÷

15° = 4 minutes

If the Earth rotates 15° in 1 hour, it will

take 4 minutes to rotate 1°:

Time-Arc Relationship

Time

24 hours

1 hour

4 minutes

1 minute

4 seconds

1 second

Arc

360°

15°

1°

15' (minutes)

1'

15" (seconds)

DIRECTION OF TRAVEL

Sun Travels at 15° per Hour

Apparent Motion of the Sun

The Sun is the

most convenient

reference for

reckoning time.

Time based on the apparent motion

of the Sun around the Earth

Solar Time

Time based on the apparent position

of the Sun from your position.

If the Sun is directly over the

meridian we are on, we say that it

is noon, local apparent time.

Apparent Time

Sun

23.5°

The Earth’s axis is inclined with respect

to the plane of its orbit around the Sun.

Sun

23.5°

Remember, the time required for a complete rotation of the Earth on its axis, relative to the Sun, varies according to the position of the Earth in its orbit.

Mean Solar Time

It would be confusing if some days had more hours and others fewer because of the Earth’s revolution; therefore mean solar time is used.

Average solar time, based on the

Sun’s apparent journey around the

Earth (360°) in exactly 24 hours

Mean Solar Time

The time at your location based on

the mean position of the Sun — that

is 1200, the mean Sun is over your

meridian, not the actual Sun

Local Mean Time (LMT)

The difference between apparent

time and the mean time

The Equation of Time

2003

DEC 31 2002

THRU

JAN 1 2004

NA

UT

ICA

L A

LM

AN

AC

Almanac

An annual publication containing a

calendar for the coming year, the times

of such events and phenomena as

anniversaries, sunrises and sunsets,

phases of the moon, tides, etc., and other

astronomical statistical information and

related topics

Almanac

Atomic Time or Universal Coordinated

Time (UTC)

Cesium Atomic Clock

An internationally agreed-upon time

scale based on the frequency of

vibrations of the radioactive cesium

atom

Atomic Time or Universal

Coordinated Time (UTC)

Time based on the relationship of the

mean Sun to the prime meridian

Greenwich Mean Time (GMT)

Local mean time along each standard

time meridian

Zone Time (ZT)

Since one hour is 15°, each time zone isbased on a division of the globe into 24zones of 15° each. A standard time-zonesystem is fixed by international agreement and by law in each country.

15°-wide zone of the Earth

that has the same time

Standard Time Zone

Zone Description (ZD)

The difference in hours between your

Zone Time (ZT) and Greenwich Mean Time

(GMT) (Use ―+‖ for longitude west, and

―-‖ for longitude east, for example +8)

Letter and a negative or positive

number for 1 to 12, east or west of

the prime meridian

Zone Description (ZD)

Zone time set ahead 1 hour

Daylight Savings Time

The practice of advancing standard

time by 1 hour in the spring of

each year and of setting it back by

1 hour in the fall in order to gain

an extra period of daylight during

the early evening

Daylight savings time is not used in navigation.

• The 180th meridian

• Separates one day from the next

International Date Line

The continental United States has four standard time zones.

Pacific Mountain Central Eastern

Eastern Standard Time (EST) is identified as +5 Romeo (R).


Central Standard Time (CST) is identified as +6 Sierra (S).


Mountain Standard Time (MST) is identified as +7 Tango (T).


Pacific Standard Time (PST) is identified as +8 Uniform (U).


291936Z NOV 03 GMTR 111420Z9 NOV 03

FM USNS SATURN

TO CNO WASH D.C.

Most information in navigational tables

and naval communications uses GMT,

so you must know how to convert the

time in any zone to GMT.

• +1 to +12 west of the Prime Meridian

• -1 to -12 east of the Prime Meridian

How Time Zones are numbered

The algebraic procedure to go from

zone time (ZT) to Greenwich time (GMT),

or to go from GMT to ZT, is:

GMT = ZT + ZD

or

ZT = GMT – ZD

Example of using ZD to find Greenwich

Time (GMT):

1830 (ZT) - 9h 00m (ZD) =

0930 Greenwich Mean Time

Example of Computing GMT

Your ship is off the coast of Somalia

(ZD = –3). The local time is 1600.

What is the GMT?

GMT = ZT + ZD

Example of Computing GMT

Your ship is off the coast of Somalia

(ZD = –3). The local time is 1600.

What is the GMT?

GMT = ZT + ZD

GMT = 1600 – 3h = 1300

Example: At 1600 on 4 July in Adak, AL

(ZD = +11), GMT is 0300 on 5 July.

Converting GMT greater than 24

Note: If your calculated GMT is greater

than 24, subtract 24 from your answer

to determine the correct GMT, which

will be one day later than your ZT.

Change the following zone times (ZT)

to Greenwich mean time (GMT):

A. 1230 at Pensacola, FL (ZD = +6)

B. 1800 at Tokyo, Japan (ZD = –9)

C. 2200 at San Diego, CA (ZD = +8)

Change the following zone times (ZT)

to Greenwich mean time (GMT):

A. 1230 at Pensacola, FL (ZD = +6)

B. 1800 at Tokyo, Japan (ZD = –9)

C. 2200 at San Diego, CA (ZD = +8)

12h 30m + 6h = 18h 30m, or 1830 GMT

18h – 9h = 9h, or 0900 GMT

22h + 8h = 30h , or 0600 GMT on the

next day(30h – 24h = 6h)

GMT – ZD = ZT

To find ZT, subtract the zone description (ZD) from GMT:

Computing ZT

Norfolk

Naval Station

GMT – ZD = ZT

You are stationed

at Norfolk, VA

(ZD = +5). GMT is

1800. What is the

local time?

Example of

Computing ZT

Norfolk

Naval Station

GMT – ZD = ZT

18h – 5h = 13h, or 1300

You are stationed

at Norfolk, VA

(ZD = +5). GMT is

1800. What is the

local time?

Example of

Computing ZT

Fairbanks, AL

Example: At 0500 GMT on 28 May, the ZT at Fairbanks, AL (ZD = +10), is 1900 on 27 May.

Note: If your calculated zone time is anegative number, subtract your answerfrom 2400 or 24 hours, to determine yourZT, which will be 1 day earlier than GMT.

Computation of ZD

A. Guantanamo, Cuba (ZD = +5; GMT = 1615)

B. Singapore (ZD = -8; GMT = 0600)

C. Honolulu, HI (ZD = +10; GMT = 0800)

Determine the (ZT) for the following

locations at the given GMT:

A. Guantanamo, Cuba (ZD = +5; GMT = 1615)

16h 15m – 5h = 11h 15m, or 1115

B. Singapore (ZD = -8; GMT = 0600)

6h – (–8h) = 14h, or 1400

C. Honolulu, HI (ZD = +10; GMT = 0800)

8h – 10h = –2h, or 2200 of the previous day

(14h – 2h = 22)

Determine the (ZT) for the following

locations at the given GMT:

Example: 1100 a.m. in Norfolk wouldbe written 1100R

In writing naval time, it is generally

required to place a time zone’s letter

after the numbers.

San Diego Naval Base

If it was 6:30 p.m. in San Diego how would you write it in naval time?

San Diego Naval Base

If it was 6:30 p.m. in San Diego how would you write it in naval time?

1830U

291936Z JUN 03

DTG

• Used in naval communications• Is placed in the message heading• Identifies when a communicationwas originated

Date/Time Group (DTG)

Date Time Group (DTG)

Example 221327Z AUG 03 means the

22nd day of August plus the time in

Greenwich mean time (GMT).

The date-time group is assigned for

identification and file purposes only.

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.

291936Z JUN 03

DTG

A message is originated at 1936Z on

29 June 2003. What is the DTG?


291936Z JUN 03

DTG

A message is originated at 1936Z on

29 June 2003.


The DTG is 291936Z JUN 03.

What is the DTG of the message?

A ship cruising off the northern coast

of Haiti sent a message at 9:00 p.m.,

August 22, 2003.

+5

230200Z AUG 03

What is the DTG of the message?

A ship cruising off the northern coast

of Haiti sent a message at 9:00 p.m.,

August 22, 2003.

+5

TIME AND NAVIGATION

THE END

What is the time used in fixing

position by celestial

navigation?

Q.1.

What is the time used in fixing

position by celestial

navigation?

Q.1.

Greenwich mean time A.1.

What is celestial navigation? Q.2.

What is celestial navigation? Q.2.

Finding position by sightings of

the Sun, stars, planets, and

Moon

A.2.

Why is a chronometer used in

celestial navigation?

Q.3.

Why is a chronometer used in

celestial navigation?

Q.3.

Because it is a very accurate

timepiece

A.3.

Why is the ship’s bell time

struck every half hour?

Q.4.

Why is the ship’s bell time

struck every half hour?

Q.4.

Bell time originated when a

ship’s timepiece was an hour

glass which ran out of sand

every half hour and had to be

turned.

A.4.

How do ships at sea ensure

their clocks are correct?

Q.5.

How do ships at sea ensure

their clocks are correct?

Q.5.

Time checks broadcast on radio

from Washington, D.C., and

Honolulu, Hawaii

A.5.

Why does the Navy use the

24-hour clock while civilians

use the 12-hour clock?

Q.6.

Why does the Navy use the

24-hour clock while civilians

use the 12-hour clock?

Q.6.

1. Old maritime custom

2. Avoid confusion in message

communications

3. Avoid possible confusion

because of A.M. and P.M.

4. To be consistent with military

time in Europe

A.6.

How would you write and say

the time 3:30 P.M. and 4:55 A.M.

in Navy time?

Q.7.

How would you write and say

the time 3:30 P.M. and 4:55 A.M.

in Navy time?

Q.7.

1530, fifteen thirty hours;

0455, zero four fifty-five hours

A.7.

How many bells should be rung

at 0730, 1430, and 2000?

Q.8.

How many bells should be rung

at 0730, 1430, and 2000?

Q.8.

7, 5, 8 A.8.

How often and why is the series

of bells on a ship repeated?

Q.9.

How often and why is the series

of bells on a ship repeated?

Q.9.

Every 4 hours to coincide with

the watch schedule

A.9.

When it is noon at our location

(longitude), what is the local

apparent time at the meridian

180 degrees away from ours?

Q.10.

When it is noon at our location

(longitude), what is the local

apparent time at the meridian

180 degrees away from ours?

Q.10.

Midnight A.10.

Why do our calendars have 366

days in a year every four years.

Q.11.

Why do our calendars have 366

days in a year every four years.

Q.11.

To account for the error in the

Earth's revolution in an

elliptical (not perfectly circular)

path around the Sun

A.11.

What is the relationship

between time and the arc of the

Sun around the Earth?

Q.12.

What is the relationship

between time and the arc of the

Sun around the Earth?

Q.12.

The Sun travels an arc of 15

degrees each hour or one

degree of arc every four

minutes.

A.12.

What is solar time? Q.13.

What is solar time? Q.13.

Time measured by using the

Sun as a reference point

A.13.

What is apparent time? Q.14.

What is apparent time? Q.14.

Time based on the apparent

position of the Sun at any

given position on the Earth

A.14.

What is mean solar time? Q.15.

What is mean solar time? Q.15.

It is the average solar time that

is a method to prevent

confusion due to the different

lengths of days.

A.15.

What is local mean time? Q.16.

What is local mean time? Q.16.

The average solar time over a

given position for a given time

throughout the year - not the

true Sun position

A.16.

What is Greenwich Mean Time

(GMT)?

Q.17.

What is Greenwich Mean Time

(GMT)?

Q.17.

The local mean time at the

Royal Observatory in

Greenwich, England

A.17.

Why is GMT important to

remember?

Q.18.

Why is GMT important to

remember?

Q.18.

By international agreement,

it is the reference time used

for navigation and

communications.

A.18.

How many time zones are there

worldwide?

Q.19.

How many time zones are there

worldwide?

Q.19.

24 A.19.

How many degrees of arc are

there in a time zone?

Q.20.

How many degrees of arc are

there in a time zone?

Q.20.

15 degrees A.20.

What does a date/time group

(DTG) include?

Q.21.

What does a date/time group

(DTG) include?

Q.21.

The date, the time, ZD (zone

description, usually Z for

GMT), month, and last 2 digits

of the year

Example: 151635Z APR 03

A.21.

How many time zones cover

the contiguous U.S.?

Q.22.

How many time zones cover

the contiguous U.S.?

Q.22.

Four, EST, CST, MST, PSTA.22.

What are zone descriptions for

the time zones around the

world?

Q.23.

What are zone descriptions for

the time zones around the

world?

Q.23.

Zone descriptions are the

numbers 1 through 12,

prefixed by + west of

Greenwich and - east of

Greenwich.

A.23.

What is the equation for

converting zone time to GMT?

Q.24.

What is the equation for

converting zone time to GMT?

Q.24.

GMT = Zone time (ZT) + Zone

description (ZD)

A.24.

What is Daylight Savings

Time?

Q.25.

What is Daylight Savings

Time?

Q.25.

Zone time set ahead one hour

(usually in the summer) to

extend the time of daylight in

the evening. It is NOT used in

navigation.

A.25.

A contrivance, consisting of a ring

or base on an axis, that permits an

object, as a ship's compass,

mounted in or on it to tilt freely in

any direction, in effect suspending

the object so that it will remain

horizontal even when its support is

tipped

Gimbals

Chronometer used

for celestial navigation.

Any unbroken part of the

circumference of a circle or

other curved line

Arc

Measurement of position east or

west from the prime meridian

Longitude

To better understand

navigation principles,

imagine the Earth

as standing still at

the center of the

universe, with the

Sun, as well as all

the other celestial

bodies, moving

around the Earth.

Produces the apparent motion of the

Sun

Rotation (of Earth)

Path the Earth takes around the Sun

Revolution (of Earth)

Time Zone Chart of

the World

Letter Designations

Each time zone has a letter designation

and zone description.

Time Zones

Time zones extend 7 ½° from either side

of a standard meridian, which are exactly

divisible by 15.

USS Dwight D. Eisenhower (CVN 69)

Remember to use the rule of algebra that

two minuses together make a plus. If we

were at a position in a time zone east of

Greenwich where the zone description

was –5, and we wanted to change a GMT

of 0600 to our standard zone time, the

formula looks like this:

GMT 0600 – ZD – (–5) = ZT 1100

time and navigation

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