The document discusses concepts of time, the solar system, Earth's movements, and how these relate to measuring and standardizing time. It covers three key points: 1) Earth's rotation on its axis and revolution around the sun cause day/night cycles and seasons. Kepler's laws describe planetary motion. 2) Time is measured using solar time, mean solar time, time zones, and Coordinated Universal Time (UTC). Conversion methods allow determining time in different locations. 3) Daylight saving time, international date line, and sunrise/sunset variations depend on factors like latitude and solar declination. Twilight durations are longest at high latitudes and when the sun's declination is highest

2. WHAT’S TIME?
HOW CAN WE MESURE IT?
WHERE ARE WE?
WHEN ARE WE?

3. THE SOLAR SYSTEM
THE SUN
9 MAJOR PLANETS
PLANETARY MOONS
2000 MINOR PLANETS & ATEROIDS

8. KEPPLER LAWS:
1. Each planet moves in an elliptical orbit with the Sun in
one foci

9. 2. The straight line joining the Sun and any planet
sweeps out equal areas in equal time intervals

10. 3. K . SP² = d³

11. RELATIVE POSITION EARTH – SUN:
• PERIHELION  Closest to the Sun
• APHELION  Furtherst from the Sun

12. EARTH’S MOVEMENTS:
1. ROTATION (West -> East)  DIURNAL CHANGES
2. ANNUAL MOVEMENT (Orbit)  Due also to axis
inclination in relation to the Sun’s ecliptic. SEASONAL
CHANGES
Elliptic movement arround Sun (one foci)
IMPORTANT POSITIONS (N.H):
SUMMER SOLSTICE  21st June
WINTER SOLSTICE  22nd Dec
VERNAL or SPRING EQUINOX  21st March
AUTUMNAL EQUINOX  23rd Sep

17. IMPORTANT FEATURES:
• Earth axis tilted 66.5º to the plane of the ECLIPTIC.
ANGLE BETWEEN EQ AND ECLIPTIC = 23.5º
Paralel of latitude directly underneath the Sun rays changes
slowly
SEASONAL CHANGES OVER THE YEAR
(DECLINATION)

18. IMPORTANT FEATURES:
DECLINATION

19. Sun at:
• Most SOUTHERLY point (Tropic of Capricorn): 22nd Dec
N.H  WINTER SOLSTICE
S.H.  SUMMER SOLSTICE
• Most NORTHERLY point (Tropic of Capricorn): 21st June
N.H.  SUMMER SOLSTICE
S.H.  WINTER SOLSTICE

20. Sun crosses the Equator:
• From South to North: 21st of March
N.H.  SPRING or VERNAL EQUINOX
S.H.  AUTUMN EQUINOX
• From North to South: 23rd of September
N.H.  AUTUMN EQUINOX
S.H.  SPRING or VERNAL EQUINOX

21. DEFINITION: The time interval that elapses between two
succesive transits of a heavenly body across the same
meridian
Earth rotation ≈ Rotation of celestial sphere
Heavenly bodies are continuosly crossing an observer’s
meridian in an East – West direction

22. Any heavenly body could be used as a timekeeper
Sun not the perfect one because its apparent speed along
the ecliptic varies
SIDEREAL DAY: Measured against any star (Unable to
relate it with light darkness periods)
SOLAR DAY: Measured against the Sun

24. APPARENT SOLAR DAY:
Time interval that elapses between two successive
transits of the actual Sun across the same meridian
APPARENT SOLAR TIME: Time based upon
the Sun as it appears on the sky,
taking as reference its transit from
the observers antimeridian.
Measured in refrence to the
apparent Sun on a particular
meridian.

25. The Sun’s real movement on the ecliptic per day is more than
360º. There are two reasons:
• The Earth is moving on an ecliptic motion arround the
Sun
• The Earth’s speed is varying arround its orbit

26. THE MEAN SOLAR DAY
Due to the fact of the Sun not moving equally on the sky
every day , and also to the fact of this variation not being
constant, we can’t consider the Real Sun giving us a practical
unit of measurement
To overcome this dificulty  IMAGINARY BODY = MEAN SUN.
Its assumed to move along the celestial equator (ecliptic)
at a uniform speed, and to complete one revolution in
nearly the mean time it takes to the true Sun to
complete one revolution in the ecliptic

27. THE MEAN SOLAR DAY
DEFINITION: Time interval between two succesive transits of
the mean Sun across the same meridian. CIVIL DAY
360º of longitude = 24 Mean solar hours
15º of longitude = 1 Mean solar hour
NOTE: Difference between Apparent and Mean days is nearly a
minute

28. EQUATION OF TIME
DEFINITION: Relation in terms of time between the Apparent
time and Mean time for a specific day. Varies
throughout the year and its due to the eccentricy* of
the Earth’s elliptical orbit arround the Sun
EQUATION OF TIME = APPARENT TIME – MEAN TIME
ECCENTRICITY = Relationship between the major and minor axes of an
ellipse. Meassures how simmilar an ellipse and a circumference are

29. EQUATION OF TIME

30. SIDERAL YEAR: Time the Earth takes to complete a full orbit
arround the Sun measured against a distant star . 365d
5h 48min 45 sec. For ease, 365days and 6hours
CALENDAR YEAR: Taken as 365days. Kept in accordance with
the calendar year by adding 1 day to the year each 4
years (Leap year)

31. DEFINITION: Time according to the Mean Sun.
The angle, converted to time, from the observers
antimeridian westwards to the Mean Sun
Diff Long (A-B)  Diff of LMT (A-B)
NOTE: A 24h period implies a 360º rotation and, because of this, 15º rotation
(CHLong) is a 1h change in time  Conversion Arc to time Chart

33. UNIVERSAL CO-ORDINATED TIME (UTC/GMT)
LMT at the Greenwich meridian (0ºE/W). Is the time
reference for aviation.
TIME CONVERSION CALCULUS BETWEEN ANY LMT AND UTC
Where a meridian is:
• East of Greenwich  Time is LATER Long WEST, UTC BEST
• West of Greenwich  Time is EARLIER Long EAST, UTC LEAST

34. DIFFERENCE BETWEEN UTC AND GMT:
Co-ordinated Universtal Time (UTC) changes at a
constant rate and is regulated agains the INTERNATIONAL
ATOMIC TIME (IAT), which is derived from atomic clocks.
UTC is regularly corrected to match GMT (LMT at the
Greenwich Meridian), but those corrections are very small.
For practical purposes, UTC equals GMT

35. UNIVERSAL CO-ORDINATED TIME (UTC/GMT):
Example 1: What’s the difference in LMT between London
Heathrow (51º 28’N 000º27’W) and Kennedy Intl (New
York) (40º38’N 073º46’W)
1. CHLong = 73º46’ – 000º27’ = 73º 19’
2. Knowing that 15º change in longitude equal 1h change in time:
73º19’ = 73.316º  73.316º · (1h/15º) = 4.887h = 4h 53min

36. UNIVERSAL CO-ORDINATED TIME (UTC):
Example 2: If the LMT in Goose Bay (060ºW) is 1200, what is
the UTC?
1. CHLong = 060ºw – 000ºE/W = 60º
2. 60º · (1h/15º) = 4.0h
3. As Goose Bay is West (Longitude west UTC best) we have to add this
difference in LMT to the time of Goose Bay to find the UTC
1200 + 4 = 1600

37. DEFINITION:
Earth is divided into 24 time zones, each of 15º of
longitude in width.
Each zone has 1h difference to the one right next to it
and uses the LMT of its central meridian as time
reference.

39. FEATURES:
• Each zone is designated by letters: zone 0 = Z,
zone -1 = A,…
• Eastern longitudes are numbered with negative zone
numbers
• Western longitudes are numbered with positive zone
numbers
• Mathematically UTC = Zone Time + Zone number

41. DEFINITION:
Time stated for a determined area in accordance with
State’s frontiers of natural geographical borders.
Sometimes listed as LOCAL TIME (LT)
Countries like USA, Canada or Australia have such a
large east-west extent that need to use multiple time
belts, each of them having its own Standard Time

43. DIFFERENCE BETWEEN STANDARD AND ZONE TIME

44. STANDARD TIME TABLES (Book):
LIST 1: Contains places where ST is normally fast on
UTC (East of Greenwich Meridian)
LIST 2:Contains places where ST is normally UTC/GMT
LIST 3: Contains places where ST is normally slow on
UTC (West of Greenwich Meridian)

45. INTERNATIONAL DATE LINE:
Whenever taking into account LMT, and moving
westwards there will be a moment in which we will get to the
Greenwich anti-meridian. There its supposed to be a -12h
LMT.
If we do the same eastwards, will get to the same
point, but with a supposed time of +12h.
Whenever we cross the 180ºE/W meridian we will
be, then, changing day, and depending on which direction we
are crossing it to, we will have to change date foreward or
backwards

46. INTERNATIONAL DATE LINE:

47. INTERNATIONAL DATE LINE:

52. EXPLANATION:
Most countries adjust their local time (ST) according to
the season of the year. When this is done, local
time is advanced one hour in the spring, and
the Daylight Saving Time (Also called Summer
Time) is in efecct. In autumn the clocks are set
back to ST again  Energy saving
Countries following this rule will be specifyied on the
ST Lists by and asterisk *

59. SUNRISE: Time moment of the day in which the upper limb of
the Sun is coincident with the observer’s visible
horizon, and the Sun’s tendency is to climb up on the
sky.
Centre of the Sun in 0.8º bellow the horizon but due to
refraction the Sun’s visible before those 0.8º

60. SUNSET: Time moment of the day in which the upper limb of
the Sun is coincident with the observer’s visible
horizon, and the Sun’s tendency is to fall bellow the
horizon.
Centre of the Sun in 0.8º bellow the horizon

61. DEPENDENT ON:
1. DATE:
• SUMMER  SR earlier and SS later
• WINTER  SR later and SS earlier
Times for SR & SS change slightly from one year to another

62. DEPENDENT ON:
2. LATITUDE:
Times for SR and SS change by several min each 3-
day period and this change is more pronounced the
higher the atitude.
For one particular latitude, all places, regardless of
longitude, will have the same LMT for SR and SS

63. DEFINITION:
Period of the day before sunrise and after sunset in
which there is still sifficient illumination for normal daylight
operations to continue.

64. Period divided into 3 stages:
CIVIL TWILIGHT – Time period between the moment of the
Sun being 6º bellow horizon until SR. Or betwee SS and
6º bellow horizon. SETS LIMIT FOR DAY-FLYING
NAUTICAL TWILIGHT - Time period betwee the 12º-bellow-
horizon position of the Sun until the Civil twilight begins
ASTRONOMICAL TWILIGHT – Time period between the
moment in which the Sun is 18º bellow horizon to the
moment the Nautical twilight begins

66. 1. VARIATION OF TWILIGHT WITH LATITUDE:
LOW LATITUDES: At the Tropics the Sun rises and sets
at almost 90º to the horizon. The period is
quite short because the way traveled is the
shortest possible
HIGH LATITUDES: The angle of the Sun approaching
the horizon is tilted, the path followed until
those 6º bellow horizon will, then, be longer
and so will be the time taken.
Lasts more at high latitudes

67. 1. VARIATION OF TWILIGHT WITH LATITUDE:
LOW LATITUDES

68. 1. VARIATION OF TWILIGHT WITH LATITUDE:
HIGH LATITUDES

69. 2. VARIATION OF TWILIGHT WITH DECLINATION:
Generally becomes larger when the Suns declination is
higher

70. 2. VARIATION OF TWILIGHT WITH DECLINATION