Local Time & Standard Time

The spinning of the earth around itself is known as rotation/axial motion.The movement of sun around the sun is called revolution/orbital motion.
Daytime changes with the seasons.The time of sunrise and sunset is not the same at all places on the meridian.It changes according to lattitude.However midday occurs at the same time at all places on the meridian.Midday occurs at different times on different meridians.
When the time at a place is given with reference to its midday,it is called the local time.There is a difference of 4 minutes in the local time of places on two meridians that are one degree apart.Countries which have a great expanse from east to west,generally adopts the local time of the central meridian as the time for the entire country.This time is called the Standard time of that country.There is a difference of 29 degrees of longitude between the easternmost place in Arunachal Padesh and westernmost place in Gujrat.It means there is difference of 1 hour 56 minutes.Indian Standard Time(IST) is based on the meridian 82 30` east.This meridian passes close to Allahabad in Uttar Pradesh
The meridian which passes Greenwich is considered as the prime meridian.Hence the difference in the standard time of different countries is told according to Greenwich time.Indian Standard Time is 5 hrs 30 min ahead of Greenwich.

Earth

Earth is flat at the poles and it bulges at the equator.The Earth rotates on its axis.
Equatorial diameter:12,756 km
Polar diameter:12,714 km
Imaginary circular lines on the earth`s surface are known as parallels.The Longest parallel is known as equator and smallest as the pole.The equator is taken to be at zero degree latitude. The Distance of a parallel from the equator is given in degrees.This distance is known as lattitude Each parallel is at distance of one degree from the next.

Meridians:Verticle semicircular lines lines are called as Meridians.
The meridian that passes through Greenwich , a town in UK,is considered to be zero degree meridian.This is known as Prime meridian.The prime meridian and the 180 degree meridian divides the earth`s sphere in two equal parts,the western & eastern hemisphere.Each meridian is at a distance of one degree from the next.There are 360 meridians on the earth`s surface.Their distance from the prime meridian is given in degrees.This distance is known as longitude.

Graticule: The network of parallels and meridians is called a graticule.

Great Circles:Biggest Circles formed by the meridians is known as great circles.

The line that separates the lighted part from the part that is in darkness is known as the Circle of Illumination.