Latitude

Latitudes are imaginary lines around the Earth parallel to the equator also called as ‘parallels’

• Characteristics
• Latitudes gradually decrease in size from the equator towards the pole
• Degree of latitude is greater at the pole (111.7 km) than at the equator (110.7 km)
• Measurements
• Latitude of a place is the angular distance measured either north or south from the equator
• Distance between the latitudes are constant
• The length of 600 latitude is half the length of the Equator
• The length of 750 latitude is 1/4th of the length of the Equator
• Important Latitudinal lines
• Arctic circle – 66*1/20 N
• Tropic of cancer -23*1/20 N
• Equator – 00
• largest of all latitudes
• also called as zero degree latitude
• Tropic of Capricorn – 23*1/2 0 S
• Antarctic circle – 66*1/2 0 S
• Sample Calculation
• What is the distance 12 degrees north of equator?
• Solution : 12 x 111.044 (average value of a degree latitude) = 1332.5 km

Longitude

Longitudes are series of semi-circles passing from north to south direction crossing the equator

• Characteristics
• All meridians are equal in length
• Meridians extend up to 1800 from the east and west of Prime meridian
• All meridians cross the equator at right angle
• Degree of longitude is greater at the equator(111.3 km) and decrease gradually towards the Pole (0 km)
• Zero degree meridian or Prime Meridian
• Chosen in 1884
• Prime meridian divides the sphere into two hemispheres
• Passes through the Royal Astronomical Observatory at Greenwich, London
• Greenwich Meridian has been adopted internationally as the standard meridian
• Measurements
• Longitude of a place is the angular distance between a point on any meridian and prime meridian at Greenwich
• Longitude of a place is measured either east or west from the Prime meridian
• Positive longitudes – longitudes counted west of Prime meridian are called positive longitudes
• Negative longitudes – longitudes counted east of Prime meridian are called negative longitudes

Revolution of the Earth

Movement

• Earth revolves round the sun once in every 365.256363004 days
• Plane of Ecliptic
• Earth revolves around the sun in an elliptical orbit “Plane of ecliptic”
• Earth equator makes an angle of 23 and ½ degrees with the plane of the ecliptic.
• responsible for change in seasons
• Earth’s axis is inclined at an angle 66 and ½ degrees with the plane of the ecliptic
• The speed of the Earth revolution along its orbit is 107,000 kph or 29.72 km/s

Effects

1. Variations in length of day and night
• Poles experience 6 months of days and 6 months of nights
• Tropics experience almost equal length of day and night
1. Change of seasons
• four divisions of the day year into spring, summer, autumn and winter marked by particular weather patterns and daylight hours
1. Distance between Earth and Sun
• The distance between Earth and Sun varies, due to the elliptical shape of the Earth’s orbit around the sun
1. Perihelion (3rd January) – The Earth is closest to the sun (147 million km)
2. Aphelion (4th July) – The Earth is farthest from the Sun (152 million km)

Change in distance between the Earth and the Sun does not cause any change in the length of day or night

1. Equinoxes
• Two days, where the sun is vertically overhead at the equator
1. Vernal Equinox (21st or 22nd March) – Sun starts to move towards Tropic of cancer
2. Autumnal Equinox (22nd or 23rd September) – Sun starts to move towards tropic of Capricorn

Insolation energy is equal in both hemispheres

1. Solstices

Either of two times of the year when the sun is at its greatest distance from the celestial equator

1. Summer solstice
• Falls on June 21st or 22nd
• Sun is vertically overhead at the tropic of cancer
• Longest day and shortest night at Northern hemisphere
• Insolation energy is greater in Northern hemisphere
1. Winter solstice
• Falls on December 21 or 22
• Sun is vertically overhead at the tropic of Capricorn
• Longest day and shortest night at Southern hemisphere
• Insolation energy is greater in Southern hemisphere
1. Leap year
• Earth takes 365 and ¼ days to complete one revolution= 365 days and 6 hours
• Every 4th year the fraction of 6 hours from the previous 3 years is cumulated and added as 29th of February to form the leap year (366 days)

Time and International Date Line

International Date Line

• It is the 1800 longitude line where the date changes by one day when crossed
• Adopted at the International Meridian Conference held in Washington in 1884
• A day is
• gained when crossed from west to east
• lost when crossed from east to west

Time

• Time advances in eastward direction and decreases in westward direction
• Places east of Greenwich gain time and places west of Greenwich lose time
• Units
• 1 Revolution of earth = 3600 or 24 hours
• 150 = 1 hour
• 10= 4 minutes
• Time zones
• World is divided into 24 standard time zones
• Each zone differs by 150 (1 hour)
• Countries with highest number of time zones
1. France – 12 time zones
2. Russia – 11 time zones
3. UK – 9 time zones
4. Australia – 8 time zones
5. Canada – 6 time zones

Kinds

• Sidereal Time
• Sidereal time is the time measured by the diurnal motion of stars
• The Sidereal day is also divided into 24 hours, each hour into 60 minutes and each minutes into 60 seconds
• Apparent Solar Time
• Apparent solar time is the time as measured by the apparent position of the sun in the sky
• Sun dial is used to measure the apparent solar time
• Apparent solar day is not of uniform length and hence, it is synchronous with regular clock speed
• Mean solar time
• Time measured based on the diurnal motion of the mean sun is called ‘Mean solar time’ or Mean Time
• Mean sun is an imaginary sun moving uniformly along the celestial equator to make a solar day of uniform length
• Mean solar time was devised to rectify the drawback in Apparent solar time
• Man solar day is divided into 24 hours, each hour into 60 minutes and each minute into 60 seconds
• Two systems
• civil time
• Astronomical time
• since 1st January 1925, Mean Solar Day began at midnight which was at noon prior to that
• Standard Time
• It is the uniform time for places in approximately the same longitude, established in a century or region by law
• India Standard Time (IST) = UTC +05:30 (Universal Time Coordinated)
• IST location : 82.50 E longitude, in Shankargarh Fort Mirzapur, (25.150 N 82.580 E), Allahabad, Up
• Local mean time of the places on the
• eastern side of Prime meridian is later than standard time
• western side of Prime meridian is earlier than standard time