Latitudes and Longitudes

Both A and R are true and R is the correct explanation of A.

Explanation — Since great circle routes are the shortest distance between the two places on the Earth and lie on the arc of a Great Circle, they are the most advantageous routes for navigators and aviators to follow.

A is true but R is false.

Explanation — IST is 5 hours 30 minutes ahead of GMT because India lies to the east of London, not the west. As the Earth rotates from west to east, places to the east of the Prime Meridian (Greenwich) are ahead in time.

We need to locate places on earth because:

1. It helps us to know the exact position of places.
2. It helps to find distance between two places if their exact positions are located.
3. It gives us an idea to locate physical features, villages, cities etc.
4. Finding location helps us to design various infrastructures like roads, railways.

The latitude of a place is the angular distance of that place North or South of the equator, as measured from the centre of the earth.

The 0° longitude passing through Greenwich near London is called the Prime meridian.

There is no higher latitude other than 90 degrees North and South because lines of latitude start at 0° (equator) and end at 90° (poles). All planes make a maximum angle of 90° from the plane of the equator.

The Lines of Longitudes are called Meridian of Longitude because the word 'meridian' means "midday" and all the places on the same meridian have their noon at the same time.

Two properties of the Lines of Latitude are:

1. Each latitude is an imaginary circle parallel to the equator and centered on the polar axis.
2. The radius and the length of parallels gradually decrease from its maxima at the equator to its minima at the poles.

Two properties of Lines of Longitude are:

1. All meridians are complete circles dividing the earth into Eastern and Western Hemisphere.
2. The longitudes are drawn 1° apart on the Equator, with 1° to 179° towards east and 1° to 179° towards west.

The whole earth represents 360° and the circumference of the earth is approximately 40,000 km. Therefore, for each degree i.e. the difference between two latitudes is 111km (i.e 40000 divided by 360).

The limit of northern temperate zone is 23 1/2°N to 66 1/2°N and the limit of southern temperate zone is 23 1/2°S to 66 1/2°S. The temperate zone stretches from Torrid zone to Frigid zone.

The Torrid zone or the tropical zones lie between the Tropic of cancer and Tropic of Capricorn which mark the limit of the overhead Sun to North and South of the Equator, i.e., 23 1/2°N to 23 1/2°S. This area receives direct sun rays and therefore, the places in the Torrid Zone are hotter than those in other zones.

The Frigid Zone experiences colder temperatures compared to other zones due to the inclination of the earth's axis, which results in the area receiving oblique rays of sunlight during the winter.

The Local Time of a place is fixed according to the central meridian of its country. When the sun is overhead on the central meridian it is 12 o'clock noon at that place. For example, the central meridian of India is 82 1/2° E and passes through Allahabad and it is the standard time line for the whole country.

Yes, it is correct to say that Local Time is the Sun Time because local time is determined based on Sun's apparent movement.

The difference in longitude between 0° and place A is 30° towards east.

Since, for every 1° difference in longitude the difference of time is 4 minutes.

Therefore, the local time of place A will be 30 x 4 = 120 minutes = 2hrs.

As, A is located to the east, it will be 2 hours ahead of Greenwich time: 12 + 2 = 14hr or 2 pm.

Therefore time at place A will be 2 pm.

The Standard Time is considered necessary because if every city had to keep the time of their own meridian, there would have been much difference in the local time of one city and the other. This would have led to a lot of confusion.

A zone on terrestrial globe that is approximately 15° longitude wide with 1 hour difference in time from other zone, is called time zone. The world is divided into 24 time zones and India has one time zone.

Singapore is situated in torrid zone, near the equator while London is located in temperate zone. Torrid zone receives direct sun rays and is hotter than the temperate zone which receives slant rays of the sun. Therefore, London experiences a lower temperature than Singapore throughout the year.

A zigzag line at roughly 180° meridian is the line which is internationally adopted as International Date Line or IDL. On either side of this line, a difference of whole day is observed. This is because the earth completes one rotation on its axis in 24 hours as it rotates from west to east.

International Date Line is for the convenience of those travelling round the world in order to avoid any confusion.

Some countries have large longitudinal extent and therefore they have many tine zones.

The 0° latitude that circumscribes the earth around it's centre is called Equator or the great circle and all other circles that do not circumscribes the earth around it's centre are called small circles.

The equator is the only latitude that circumscribes the earth around it's centre and therefore it is the largest latitude. All other latitudes, either in north or in south, are smaller than equator because they do not circumscribe the earth around its centre.

The use of local time is inconvenient in practical life because local time is different in different countries. For those travelling abroad, it is very confusing to have different time zones.

A grid is a network of evenly spaced horizontal and vertical lines used to identify locations on a map. Earth's grid refers to the network of latitudes and longitudes on the earth's surface.

The first mathematician to have measured the circumference of the Earth was Eratosthenes.

The important Climatic Zones of the World are:

1. The Torrid or tropical zones
2. Temperate zones
3. Frigid zones

For every 1° change in longitude, the change in time is 4 minutes.

The latitudes and longitudes are horizontal and vertical lines which form a grid on the globe or map. We can easily locate a place on the globe if we have its longitudinal and latitudinal positions. The point of intersection of its latitude and longitude will determine the position of that place on globe.

1. Latitude
2. Longitude
3. 40° N

1. Difference between Local Time and Standard Time:

2. Difference between Parallels and Meridians:

3. Difference between Equator and Prime Meridian:

The longitudinal difference between England and India: is 82° 30'.

For 1° longitudinal difference time is 4 minutes.

So, for 82° 30' longitudinal difference is 82° 30' x 4 = 330 minutes or 5 hours 30 minutes.

As India is situated in the east of England, the local time of India will be ahead the time of England.

The local time of India will be: 12 noon + 5 hours 30 minutes = 5:30 pm.

The longitudinal difference between New York and Greenwich is: 74°

For 1° longitudinal difference time is 4 minutes.

So, for 74° longitudinal difference the time difference is: 74° x 4 = 296 minutes or 4 hours 56 minutes.

As New York is situated in the west of Greenwich, its local time will be behind the time of Greenwich.

The local time of New York will be: 12 noon - 4 hours 56 minutes = 7:04 am.

The longitudinal difference between Helsinki and India is: 82° 30' - 20° = 62° 30'

For 1° longitudinal difference time is 4 minutes.

So, for 62° 30' longitudinal difference the time difference is 62° 30' x 4 = 250 minutes or 4 hours 10 minutes.

As Helsinki is situated in the west of India, the local time of Helsinki will be behind the time of India.

The local time of Helsinki will be: 10 pm - 4 hours 10 minutes = 5:50 pm.

The longitudinal difference between Auckland and Wollongong is: 175° - 150° = 25°

For 1° longitudinal difference time difference is 4 minutes.

So, for 25° longitudinal difference time difference is 25° x 4 = 100 minutes or 1 hour 40 minutes.

As Auckland is situated in the east of Wollongong, the local time of Auckland will be ahead the time of Wollongong.

The local time of Auckland will be: 2 pm + 1 hours 40 minutes = 3:40 p.m.

The longitudinal difference between village A and village B is: 120° + 75° = 195° (as different hemisphere).

For 1° longitudinal difference time is 4 minutes.

So, for 195° longitudinal difference the time difference is: 195° x 4 = 780 minutes or 13 hours.

As village B is situated in the east of village A, its local time will be ahead the time of village A.

The local time of village B will be: 5pm + 13 hours = 6 a.m. on Saturday.

Equator

66 1⁄2°N

181

Torrid Zone

4 minutes

International Date Line

82 1⁄2°E

6

They are used to determine time

Midday

5 hours 30 mins

Equator & all the meridians are Great circles.

24

The latitude of a place is the angular distance of that place North or South of the equator, as measured from the centre of the earth.

The longitude of a place is the angular distance of that place east or west of the prime meridian.

The imaginary lines or semi-circles that connect north pole and south pole are called meridian.

Prime Meridian is the longitude of 0° which connects north and south poles and passes through Greenwich near London.

When the sun is overhead at a place, the local time is 12 o'clock noon at that place. Local time of a place can also be calculated if we know the longitude of the place.

Standard time of a country is defined as the local time of its central meridian which is observed throughout the country.

The longitude of 82 1/2°E is the central meridian of India which passes through Allahabad. Its local time is the standard time for the country and is known as Indian Standard Time.

The local time of zero degree meridian which passes through the Royal Astronomical Observatory at Greenwich, is taken as international standard time and is known as Greenwich Mean Time.

The longitude at 180° is considered as International Date Line as on either side of this line, a difference of one whole day is observed.

The latitude at 0° which circumscribe the earth around it's centre and divides the earth into two hemispheres is called Great circle.

All other latitudes except the equator are smaller (than the equator) and are known as Small circles.

A grid is a network of evenly spaced horizontal lines (latitudes) and vertical lines (longitudes) used to identify locations on a map.

Below diagram shows Parallels of Latitude:

Below diagram shows Temperature Zones:

Below diagram shows Earth's Grid:

Latitudes and Longitudes are always expressed in angles because they represent angular distance as the earth is spherical in shape.

Large countries have larger longitudinal extent and therefore they have many time zones. For example, Canada has 6 time zones.

The International Date Line is not a straight line like other longitudes because in order to avoid any landmass, deviation has been taken. It is done to avoid the confusion of having different dates in the same country.

A person gains time as he travels towards east because the earth rotates from west to east. Places on the east of a given point on the earth are ahead of time.

The intervals between successive parallels are constant because the latitudes are parallel and equidistant to each other.

A person travelling from Mumbai to London has to alter his watch because both the cities are in different time zones.

The difference between longitudes of I.S.T. and the G.M.T. = 82 1/2°

Since, the difference of 1° in longitude = a difference of 4 minutes

Therefore, for difference of 82 1/2°, the difference in time = 4 x 82 1/2 = 330 minutes = 5 hrs 30 min.

Since shape of the Earth is an oblate spheroid, the radius and length of parallels gradually decrease from its maxima at the Equator to its minima at the Poles. Hence, parallels are not equal in length.

Navigators use Great circle route for navigation because Great circle routes are the shortest distance between the two places on the Earth. They help to save fuel and time so they are very economical.

Arunachal Pradesh lies in the easternmost part of India, where the sun rises and sets much earlier than in the rest of the country. Since India follows a single standard time, government offices there start at 10 am, by which time a significant portion of daylight has already passed. As a result, valuable daylight hours are lost, reducing the number of productive working hours for people in the region.

This happened because Magellan’s crew had unknowingly crossed the 180° meridian during their journey. When a ship travels around the world and crosses this line from west to east, it gains a day due to the 24-hour time difference on either side of the 180° meridian. So, although they believed it was 5th September, the actual date was 6th September.