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Summary

Geography Class 03

## Last class revision (5:12 PM)

- Latitude and longitude.
- Rotation and revolution.

## Seasons (5:25 PM)

- ***Tabular presentation for various cases of earth's movement:***
- |  |  |  |
  | --- | --- | --- |
  | Conditions | The angle of incidence(intensity). | Length of the day |
  | Case 1:  No rotation.  No tilt.  No revolution. | 90 degrees at the equator(higher intensity).  0 degrees at the poles(lower intensity). | 24 hrs of day or night. |
  | Case 2:  Rotation is present.  No tilt.  No revolution. | 90 degrees at the equator(higher intensity).  0 degrees at the poles(lower intensity). | 12 hrs of the day and 12 hrs of the night across all the latitudes. |
  | Case 3:  Rotation is present.  Tilt(northern hemisphere towards the sun) is present.  No revolution. | 90 degrees at 23.5 degrees north.  The intensity is higher in the northern hemisphere than in case 2.  In the southern hemisphere lower intensity than in case 2. | Equator- 12 hrs of day and night.  The length of the day increases toward the northern hemisphere and decreases toward the southern hemisphere. |
  | Case 4:  Rotation, tilt, and revolution all are present. | 90 Degrees at 23.5 degrees south.  The southern hemisphere has a higher intensity than case 2.  The northern hemisphere has a lower intensity than case 2. | Equator- 12 hrs of day and night.  length of the day increases in the southern hemisphere and decreases in the northern hemisphere. |
- Seasons are periods of the year that are characterized by specific climatic conditions.
- There are 4 seasons- Summer, Autumn, Winter, and Spring.
- Seasons are observed on the earth because the earth revolves around the sun with a tilted axis of rotation whose angle of inclination is always constant.
- This causes variations in the intensity of sunlight and length of day throughout the year resulting in seasons
- The regions receiving higher intensity of sunlight for a longer duration experience higher temperatures resulting in summer.
- Those regions receiving lower intensity of sunlight for shorter duration experience winters.
- ***Diagramatic representation of earth and sun relation:***
- ***![](https://slideplayer.com/slide/2855524/10/images/16/Earth+Sun+Relations+Spring+Equinox+3%2F21+Summer+Solstice+6%2F21.jpg)***
- ***Summer solstice:***
- It occurs on 21st June.
- The sun's rays fall vertically at the tropics of cancer(23.5 degrees N).
- The intensity of sunlight has increased in the northern hemisphere.
- The length of the day increases from the equator to the north pole.
- ***Winter solstice:***
- It occurs on 22 December.
- Sun rays fall vertically at the tropic of Capricorn(23.5 degrees S).
- The location of the southern hemisphere are receiving higher intensity of sunlight and those in the northern hemisphere lower intensity of sunlight.
- The length of the day decreases from the equator to the north pole.
- ***Equinox:***
- It happens on the 21st of March(Spring Equinox) and the 23rd of September(Autumn Equinox).
- The sun's rays are falling vertically at the equator.
- The length of the day is 12 hrs along all the latitudes.

## Video related to seasons (6:31 PM).

## The extent of day and night (6:49 PM)

- ***Position of the overhead sun:***
- It is a position where 90-degree sunlight falls.
- The position of the overhead sun is always between 23.5 Degrees N and 23.5 Degrees S.
- Every location between the Tropic of cancer and the Tropic of Capricorn will receive, at least 2 days of 90-degree sunlight and those which are located exactly in the tropics receive 90-degree sunlight only once.
- ***Polar day:***
- It is experienced in regions with 24 hours of daylight.
- The maximum extent of a polar day is 66.5 degrees N and S.
- ***Polar night:***
- It is when there are 24 hours of darkness.

## Time Zones (7:20 PM)

- A time zone is a region of the globe that observes uniform standard time.
- The entire globe is divided into 24 time zones with the Greenwich meridian as a standard reference.
- The time along a particular longitude always remains the same.
- From the Greenwich meridian towards the east the time increases(EGA- east gain addition), and towards the west time decreases(WLS-west lose subtraction).
- With a change of every 15 degrees time changes by 60 mins, therefore with a change of every 1 degree, time changes by 4 mins.
- India follows 82.5 degrees east as Indian standard time.
- ***Multipule time zones:***
- India followed 3 time zones based on Bombay, Calcutta, and Madras, along with local Chaibagan time in Assam.
- In 1906 India adopted 82.5 degrees east as Indian standard time(IST) and the local time zones of Bombay and Calcutta were continued till 1955.
- The longitudinal extent of nearly 30 degrees between East and West has resulted in a Mismatch of the Sun cycle and human activities.
- ***Issues in adopting multiple time zones in India:***
- Economic integration- banking, stock exchange, etc.
- Administrative convince- offices, schools, etc.
- Issues in synchronization of transportation- Railways.
- Communication gap impacting security.

## The topic of the next class:  International Date Line and Origin of the Universe.