Phase 1

Theoretical rising and setting of sun Visible rising and setting of sun Factors affecting sunrise and sunset Continuous sunlight.

Phase 2

Extraction of Sunrise & Sunset times - Air Almanac Corrections for Height of the Observer

THEORETICAL SUNRISE AND SUNSET

“The theoretical sunrise or sunset is said to

occur when the centre of the Sun is on the

Celestial Horizon of the observer”.

THEORETICAL SUNRISE

Celestial Horizon

THEORETICAL SUNSET

Celestial Horizon

Z

NCP

C

H

E Q

Z

NCP

C

H

E Q

SCP SCP

THEORETICAL SUNRISE AND SUNSET

90º 90º

Altitude of sun is 0 & Zenith Distance 90

VISIBLE SUNRISE AND SUNSET

“ When the upper limb of the sun is on the visible

horizon, visible sunrise or visible sunset is said to occur.

At visible s/r or s/s the body has a depression equal to

atmospheric refraction + the Semi-diameter (SD) of the

sun below the sensible horizon.

VISIBLE SUNRISE & SUNSET

Refraction

Visible Horizon

Sensible Horizon

SUN’S DEPRESSION

Visible Horizon

Sensible Horizon

Refraction

Semi-Diameter

Depression

DEPRESSION

At sunrise or sunset the upper limb of the sun is on the visible horizon, its depression below the celestial or sensible horizon is Depression = Atmospheric refraction at 0 alt + Semi diameter = 34 ’+ 16’Depression = 50 ’

Zenith distance = 90 50’

The prediction of timings of sunrise and sunset tabulated in the Air Almanac are calculated using this value.

FACTORS AFFECTING

SUNRISE AND SUNSET.

FACTORS AFFECTING

SUNRISE AND SUNSET

• Declination• Latitude• Longitude• Height of the observer

VARIATION x DECLINATION

Dec- 20

Dec- d1

Dec- d2VH

Z

NCP

EQ

NCP

EQ

VH

Dec- 10

Dec- Lat Same Name Dec- Lat Contrary Name

VARIATION WITH DECLINATION

When the sun’s declination is of the same name to the observers latitude Sun rises early and sets later with increase in sun’s declination.

When the sun’s declination is of the contrary name to the observers latitude Sun rises later and sets early with increase in sun’s declination.

VARIATION OF SUNRISE - LATITUDE

Sun’s Daily Path

Dec & Lat - Same Name

Sun rises Earlier with increase in latitude

VH 1

Z1

VH 2

Z2

NCP

EQ

Declination Same Name

VARIATION OF SUNSET - LATITUDE

Dec & Lat - Same Name

Sun sets Later with increase in latitude

Sun’s Daily Path

VH 1

Z1

VH 2

Z2

NCP

EQ

Declination Same Name

VARIATION OF SUNRISE - LATITUDE

Sun’s Daily Path

Dec & Lat - Contrary Name

Sun rises Later with increase in latitude

VH 2

Z2

VH 1

Z1

NCP

EQ

Declination Contrary Name

VARIATION OF SUNSET - LATITUDE

Dec & Lat - Contrary Name

Sun Sets Earlier with increase in latitude

Sun’s Daily Path

VH 2

Z2

VH 1

Z1

NCP

EQ

Declination Contrary Name

VARIATION WITH LATITUDE

When the sun is in the observer’s

hemisphere it rises earlier and sets later the

increase in observers latitude.

When sun is on the other hemisphere

it rises later and sets earlier with increase in

latitude.

VARIATION WITH LONGITUDE

For a given latitude and declination the local times of

sunset and sun rise for all meridians will be the same since the

relationship between times and that between hour angles are

comparable.

LHA = GHA + LONG (E/W) and

LMT = GMT + LONG (E/W) converted in time.

Thus if the declination is constant on a given latitude the

local time of rising or setting at Greenwich (GMT) would be the

same as the LMT of that at any other meridian

VARIATION WITH HEIGHT

For an Observer at a height

Sun rises Earlier and sets Later

Horizon at sea level

Horizon at 20,000 ft

Sunrise at 20,000 ft

Sunrise at sea level

Observer at 20,000 ft

HEIGHT OF THE OBSERVER

With an increase of height the sun rises earlier and sets

later due to the change in the plane of the observers

horizon.

CONTINUOUS SUNLIGHT AND

NO SUNLIGHT

At higher latitudes the sun may be above the

horizon throughout the day. This is known as

Continuous Sunlight.

Similarly sun can also be below the horizon

and not visible throughout the day which is called

No Sunlight

Calculate the Sunrise for 33 20 N, 115 13E,

on 01 Jan 1987.

Page no A130;

For 02 Jan.

Time of sunrise for 35 N = 07 08

Time of sunrise for 30 N = 06 56

Sunrise for 33 20’ N = 0704 (LMT)

Calculate the Sunrise for 78 N, on 10 Mar 1987.

Page no A153;

Time of merpass = 12 10

The semi duration from graph = 4:45

LMT of Sunrise = 1210 - 4:45 = 0725

Similarly LMT sunset = 1655