Latitude and longitude
Latitude and Longitudes
Eratosthenes was the first person to calculate the size of the earth. He realized that Earth could be located with a basic grid of lines called Longitudes and Latitudes.
Latitude
- Latitude is the angle between the equatorial plane and the axis. Lines joining points of the same latitude are called parallels. Equator {0° parallel} itself is the largest parallel and only circle of latitude which also is a great circle. The Equator is also used as the fundamental plane of all geographic coordinate systems.
- There are 180° of latitudes and each degree of latitude spans around 111 kilometers or 69 miles or 60 Nautical miles. But this distance varies because Earth is not a perfect sphere.
- From the Equator to 40° towards both poles it is slightly less than 111 kilometers and from 41° towards both poles, it is slightly more than 111 kilometers.
- The 90° North and 90° South are not circles but only reference points. Latitudes tell us the temperature and climatic position of a particular place
Fun fact
An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the centrifugal force exerted by the rotation about the body’s axis.
Important parallels of latitudes
There are four important parallels /latitudes–
Tropic of Cancer (23½° N) in the northern hemisphere.
Tropic of Capricorn (23½° S) in the southern hemisphere.
Equator (0°)
Arctic circle at 66½° north of the equator.
Antarctic circle at 66½° south of the equator.
Latitudinal Heat zones of the earth
There are 3 zones
Torrid Zone
Temperate Zone
Frigid Zone
Torrid Zone or Tropical Zone
The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the torrid zone.
Temperate Zones
The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn.
The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic circle in the northern hemisphere, and the Tropic of Capricorn and the Antarctic circle in the southern hemisphere, have moderate temperatures. These are, therefore, called temperate zones.
Frigid Zones
Longitude is an angular distance, measured in degrees along the equator east or west of the Prime (or First) Meridian.
On the globe longitude is shown as a series of semi-circles that run from pole to pole passing through the equator. Such lines are also called longitudes.
The zero meridian is the one that passes through the Royal Astronomical Observatory at Greenwich, near London. This is the Prime Meridian (0°) from which all other meridians radiate eastwards and westwards up to 180°.
As the parallels of latitude become shorter poleward, the meridians of longitude converge at the poles.
They have one very important function, they determine local time in relation to G.M.T. or Greenwich Mean Time, which is sometimes referred to as World Time.
Longitude
Longitude is an angular distance, measured in degrees along the equator east or west of the Prime (or First) Meridian.
On the globe longitude is shown as a series of semi-circles that run from pole to pole passing through the equator. Such lines are also called longitudes.
The zero meridian is the one that passes through the Royal Astronomical Observatory at Greenwich, near London. This is the Prime Meridian (0°) from which all other meridians radiate eastwards and westwards up to 180°.
As the parallels of latitude become shorter poleward, the meridians of longitude converge at the poles.
They have one very important function, they determine local time in relation to G.M.T. or Greenwich Mean Time, which is sometimes referred to as World Time.
Longitude and Time
Since the earth makes one complete revolution of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes.
The earth rotates from west to east, so every 15° we go eastwards, local time is advanced by 1 hour. Conversely, if we go westwards, local time is retarded by 1 hour.
We may thus conclude that places east of Greenwich see the sun earlier and gain time, whereas places west of Greenwich see the sun later and lose time.
The International Date Line
A traveler going eastwards gains time from Greenwich until he reaches the meridian 180°E, when he will be 12 hours ahead of G.M.T.
Similarly, in going westwards, he loses 12 hours when he reaches 180°W. There is thus a total difference of 24 hours or a whole day between the two sides of the 180° meridian.
This is the International Date Line where the date changes by exactly one day when it is crossed. A traveler crossing the dateline from east to west loses a day (because of the loss in time he has made), and while crossing the dateline from west to east he gains a day (because of the gain in time he encountered).
The International Date Line in the mid-Pacific curves from the normal 180° meridian at the Bering Strait, Fiji, Tonga, and other islands to prevent confusion of day and date in some of the island groups that are cut through by the meridian.
Note:
The Indian Government has accepted the meridian of 82.5° east for the standard time which is 5 hours 30 mins, ahead of Greenwich Mean Time. The five states in India through which the Indian Standard Meridian (82.5′ E) passes are Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Odisha, and Andhra Pradesh.
Food for Brain
British colonialists introduced a time schedule “chaibagaan time” or “bagaan time”, for tea planters, which was one hour ahead of IST.
Now the administration of the Indian state of Assam now wants to change its time zone back to Chaibagaan time to conserve energy and improve productivity. But Indian government didn’t accept to such a proposal.
Lunar Eclipse
Lunar eclipse takes place when the Moon moves into the Earth’s shadow. The Earth has to be directly between the Sun and the Moon.
Lunar eclipse can only take place during a full Moon.
First, the Moon moves into the penumbra – the part of the Earth’s shadow where not all of the light from the Sun is blocked out. Part of the Moon’s disc will look dimmer than a regular full Moon.
And then the Moon moves into the Earth’s umbra, where direct light from the Sun is totally blocked out by the Earth. This means the only light reflecting off the Moon’s disc has already been refracted, or bent, by the Earth’s atmosphere
Total Solar Eclipse
Total solar eclipses occur when the New Moon comes between the Sun and Earth and casts the darkest part of its shadow, the umbra, on Earth. A full solar eclipse, known as totality, is almost as dark as night.
During a total eclipse of the Sun, the Moon covers the entire disk of the Sun. In partial and annular solar eclipses, the Moon blocks only part of the Sun.
When the Moon completely covers the disk of the Sun, only the Sun’s corona is visible.
It is called Total eclipse because at the maximum point of the eclipse (midpoint of time of totality), the sky goes dark and temperatures can fall.