The Earth, Solar System, Latitude and Longitude
The Earth, Solar System, Latitude and Longitude
Geography is the fifth equal part of the 40-question Part-II paper, so expect about 8 questions from it. This opening topic supplies 1 to 2, almost always on planets, the grid of latitudes and longitudes, or Indian Standard Time. The facts are fixed and highly scoreable.
The Solar System
Eight planets orbit the Sun. In order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
| Planet | Remembered as |
|---|---|
| Mercury | Closest to the Sun and the smallest planet |
| Venus | Hottest planet; Earth's twin; the morning and evening star |
| Earth | The blue planet; the only one known to support life |
| Mars | The red planet |
| Jupiter | The largest planet |
| Saturn | Known for its rings; least dense planet |
Venus and Uranus rotate from east to west, opposite to the rest. The Moon is Earth's only natural satellite and takes about 27 days to orbit the Earth.
Rotation and Revolution
- Rotation — the Earth spins on its axis in about 24 hours, causing day and night.
- Revolution — the Earth goes round the Sun in about 365 and a quarter days, causing seasons.
- The quarter day is why a leap year of 366 days comes every fourth year.
- The Earth's axis is tilted at about 23.5 degrees, and this tilt, not the distance from the Sun, causes the seasons.
✗ Seasons happen because the Earth moves closer to and farther from the Sun | ✓ Seasons are caused by the tilt of the Earth's axis during revolution
Latitudes and Longitudes
| Line | Value | Note |
|---|---|---|
| Equator | 0° | Divides Earth into two hemispheres |
| Tropic of Cancer | 23.5° N | Passes through India |
| Tropic of Capricorn | 23.5° S | — |
| Arctic Circle | 66.5° N | — |
| Antarctic Circle | 66.5° S | — |
| Prime Meridian | 0° | Passes through Greenwich |
Latitudes are parallel to each other and are called parallels. Longitudes meet at the poles and are called meridians. There are 181 parallels and 360 meridians in all.
Time and the Indian Standard Meridian
1° of longitude = 4 minutes of time
The Earth turns 360 degrees in 24 hours, which is 15 degrees an hour. India's standard meridian is 82.5 degrees East, passing through Mirzapur in Uttar Pradesh, which puts Indian Standard Time 5 hours 30 minutes ahead of Greenwich Mean Time. The International Date Line runs roughly along 180 degrees.
रितुएँ पृथ्वी के झुकाव (23.5°) से बनती हैं, सूर्य से दूरी से नहीं।
TRE pointer: The examiner's favourite here is the seasons question, where the wrong option blames distance from the Sun instead of the axial tilt. The second favourite is the Indian Standard Time calculation. Because you will teach this to class 6, the paper expects you to state the cause correctly, not approximately. Recall the marking rule as well — five options A to E, −1/3 for a wrong answer, and option E must be marked to skip.
60-Second Recap
- Eight planets; Mercury smallest and closest, Jupiter largest, Venus hottest.
- Venus and Uranus rotate east to west.
- Rotation gives day and night; revolution plus a 23.5 degree tilt gives seasons.
- Equator 0 degrees; Tropics at 23.5; Arctic and Antarctic Circles at 66.5.
- 181 parallels and 360 meridians; Prime Meridian passes through Greenwich.
- India's standard meridian is 82.5 degrees East through Mirzapur; IST is GMT plus 5:30.
Frequently Asked Questions
Why does the Earth have seasons?
Because its axis is tilted at about 23.5 degrees as it revolves around the Sun, so different parts receive direct sunlight at different times of the year. The common wrong answer is that the Earth moves nearer to and farther from the Sun, which is not the cause of the seasons.
What is India's standard meridian and why 82.5 degrees East?
It is 82.5 degrees East, passing through Mirzapur in Uttar Pradesh. It was chosen because it runs roughly through the middle of the country's east-west spread, giving a single practical time for the whole country. It places Indian Standard Time five and a half hours ahead of GMT.
What is the difference between latitude and longitude?
Latitudes are horizontal lines parallel to the Equator and never meet, which is why they are called parallels. Longitudes run from pole to pole and all meet at the poles, which is why they are called meridians. There are 181 parallels and 360 meridians.
Which planet is called Earth's twin and why?
Venus, because it is almost the same size and mass as Earth and has a similar composition. It is also the hottest planet due to its thick carbon dioxide atmosphere, and it is visible as the morning and evening star. Do not confuse it with Mars, the red planet.