Rotation, axis and equator
A spinning top turns on one point and stays upright. A globe on a table also turns around a rod passing through it. The earth turns in the same way.
Rotation (परिवलन) is the turning of an object around itself. The imaginary line it turns around is the axis (आस).
Rule 1: Axis and poles — The earth's axis is inclined (तिरकी). Its two ends are the north pole (N) and the south pole (S).
In the figure : In the figure the earth's axis is inclined; the equator divides it into the northern and southern hemispheres.
- Easy : Easy: A top rotates around its axis.
- Medium : Medium: The earth's axis is tilted, not straight up.
- Exam-type : Exam: The axis joins the north pole and the south pole.
Rule 2: Equator and hemispheres — The equator (विषुववृत्त) is the imaginary circle midway between the poles. It divides the earth into the northern hemisphere and the southern hemisphere (गोलार्ध).
- Easy : Easy: The equator is halfway between the poles.
- Medium : Medium: India is in the northern hemisphere.
- Exam-type : Exam: "Hemi" means half, so a hemisphere is half a sphere.
Rotation = turning around the axis. Equator makes two hemispheres.
Thinking the axis is a real rod. It is imaginary.
Memory clue: "आस = काल्पनिक दांडा, विषुववृत्त = मधला पट्टा".
Spot the difference
| Term | Meaning |
|---|---|
| Rotation | Turning around axis |
| Axis | Imaginary line, inclined |
| Equator | Circle midway between poles |
| Hemisphere | Half of the earth |
Practice questions
- 1What is rotation?
- 2What is the axis?
- 3Name the two poles.
- 4What is the equator?
- 5Name the two hemispheres.
- 6Is the earth's axis straight or inclined?
- 7In which hemisphere do you live?
- 8If the equator cuts the earth into two equal halves, what is each half called?
Show answers (try them yourself first)
- 1Turning of an object around itself.
- 2The imaginary line around which the earth turns.
- 3North pole and south pole.
- 4The imaginary circle midway between the poles.
- 5Northern and southern.
- 6Inclined.
- 7Northern hemisphere.
- 8A hemisphere.
Day, night and hours
When you spin on a swing facing a lamp, the lamp is in front of you, then behind you, then in front again. Day and night come in the same way as the earth turns before the sun.
The earth rotates from west to east. One rotation takes one day of 24 hours.
Rule 1: Day and night — The half of the earth facing the sun has day. The half turned away has night. As the earth turns, every place gets day and night one after the other.
In the figure : In the figure the half facing the sun has day and the other half has night.
Day, night and hours
In the app you can move this figure with your finger.
Open in the app- Easy : Easy: The sun seems to rise in the east.
- Medium : Medium: The candle is the sun and the globe is the earth in the model.
- Exam-type : Exam: Sunrise, noon and sunset happen because the earth rotates.
Rule 2: The 24 hours — One rotation = 1 day = 24 hours. So in half a day there are 12 hours, and two rotations make 2 × 24 = 48 hours.
- Easy : Easy: 1 day = 24 hours.
- Medium : Medium: 3 days = 3 × 24 = 72 hours.
- Exam-type : Exam: The earth turns from west to east, so the sun seems to move east to west.
Rotation: west to east, 24 hours, gives day and night.
Thinking the sun goes around the earth every day. The earth rotates.
Memory clue: "पश्चिम → पूर्व, 24 तास, दिवस-रात्र".
Spot the difference
| Item | Fact |
|---|---|
| Direction | West to east |
| One rotation | 1 day = 24 hours |
| Result | Day and night |
Practice questions
- 1In which direction does the earth rotate?
- 2How long is one rotation?
- 3What causes day and night?
- 4Which half of the earth has day?
- 5How many hours are there in 2 days?
- 6Why does the sun seem to move across the sky?
- 7In the candle and globe model, what does the candle show?
- 8It is noon in Mumbai. Is that half of the earth facing the sun or away?
Show answers (try them yourself first)
- 1West to east.
- 2One day, 24 hours.
- 3Rotation of the earth.
- 4The half facing the sun.
- 548 hours.
- 6Because the earth rotates.
- 7The sun.
- 8Facing the sun.
Year, leap year and seasons
Your birthday comes once a year. The earth takes one year to go round the sun once, so the same date returns after a year.
Revolution (परिक्रमा) is the earth's journey around the sun. One revolution = one year, about 365 days and 6 hours.
Rule 1: Leap year — The extra 6 hours of each year add up: 4 × 6 = 24 hours = 1 day. So every fourth year has 366 days and February has 29 days. This is a leap year (लीप वर्ष).
In the figure : In the figure the extra 6 hours add up to one extra day, 29 February, every fourth year.
- Easy : Easy: A year has about 365 days.
- Medium : Medium: A leap year has 366 days.
- Exam-type : Exam: 2024 is divisible by 4, so it was a leap year.
Rule 2: Seasons — The revolution together with the inclined axis causes seasons (ऋतू). In India we feel summer, rainy season and winter; the six seasons together are the rituchakra (ऋतुचक्र).
In the figure : In the figure the six seasons come one after another and repeat every year.
Year, leap year and seasons
In the app you can move this figure with your finger.
Open in the app- Easy : Easy: Rainy season comes after summer.
- Medium : Medium: There are six seasons in the rituchakra.
- Exam-type : Exam: Without the inclined axis there would be no seasons.
Revolution = 1 year = 365 d 6 h. Leap year every 4 years. Revolution + tilt = seasons.
Thinking seasons come because the earth is nearer or farther from the sun. The tilt and revolution cause them.
Memory clue: "4 × 6 तास = 1 दिवस → लीप वर्ष".
Spot the difference
| Motion | Result |
|---|---|
| Rotation | Day and night |
| Revolution | Year |
| Revolution + tilt | Seasons |
Practice questions
- 1What is revolution?
- 2How long does one revolution take?
- 3How many days are there in a leap year?
- 4Which month has 29 days in a leap year?
- 5How many seasons are there in the rituchakra?
- 6What causes seasons?
- 72028 is divisible by 4. How many days does that year have?
- 8How many extra hours collect in 8 years? How many leap days?
Show answers (try them yourself first)
- 1The earth's journey around the sun.
- 2About 365 days and 6 hours (one year).
- 3366.
- 4February.
- 5Six.
- 6Revolution and the inclined axis.
- 7366 days.
- 88 × 6 = 48 hours = 2 days.
Phases of the moon
A mirror held in a dark room shines only when light falls on it. The moon is like that mirror; it shines only because the sun lights it.
The moon has no light of its own. Its changing lit shapes, seen from the earth, are the phases of the moon (चंद्रकला).
Rule 1: Full moon and new moon — We always see only one side of the moon. On a full moon (पौर्णिमा) the whole face is lit. On a new moon (अमावस्या) none of it is seen.
In the figure : In the figure the moon shines only by sunlight, so we see different lit parts, called phases.
Phases of the moon
In the app you can move this figure with your finger.
Open in the app- Easy : Easy: Full moon: the whole face is lit.
- Medium : Medium: New moon: the face is not seen.
- Exam-type : Exam: The moon does not change shape; only the lit part we see changes.
The moon shines by sunlight. Full moon = all lit. New moon = none seen.
Thinking the moon's own shape changes. Only the lit part we see changes.
Memory clue: "चंद्र = आरसा, सूर्य = दिवा".
Spot the difference
| Phase | What we see |
|---|---|
| Full moon | Whole face lit |
| New moon | Nothing seen |
Practice questions
- 1Does the moon have its own light?
- 2What are the phases of the moon?
- 3How many sides of the moon do we see?
- 4What do we call the day when the whole face is lit?
- 5What do we call the day when the moon is not seen?
- 6Why do we see different shapes of the moon?
- 7Is the moon a source of light like the sun?
- 8On a new moon night, does the moon cease to exist?
Show answers (try them yourself first)
- 1No, it shines by sunlight.
- 2Changing shapes of the lit part seen from the earth.
- 3Only one.
- 4Full moon (Pournima).
- 5New moon (Amavasya).
- 6We see different lit parts of it.
- 7No, it only reflects sunlight.
- 8No, it is there but its lit side is turned away from us.
Lunar month and tithis
A diary has a date for each day. In the old calendar, people counted days by watching the moon grow and shrink.
The lunar month (चांद्रमास) is the time from one new moon to the next, 28–30 days. Each day of it is a tithi (तिथी).
Rule 1: Waxing and waning — From new moon to full moon (14–15 days) the lit part grows: waxing moon or Shukla Paksha (शुक्ल पक्ष). From full moon to new moon the lit part shrinks: waning moon or Krishna Paksha (कृष्ण पक्ष).
- Easy : Easy: Shukla Paksha: the moon grows.
- Medium : Medium: Krishna Paksha: the moon shrinks.
- Exam-type : Exam: Pournima comes at the end of Shukla Paksha.
Rule 2: Tithi counting — A lunar month has two pakshas, each of about 14–15 days. So 2 pakshas make about 28–30 days.
- Easy : Easy: 2 pakshas make 1 lunar month.
- Medium : Medium: 15 + 15 = 30 days.
- Exam-type : Exam: A month from one Amavasya to the next is the lunar month.
Shukla = waxing; Krishna = waning; lunar month = 28–30 days.
Mixing up Shukla and Krishna. Shukla grows; Krishna shrinks.
Memory clue: "शुक्ल = शुभ्र वाढ, कृष्ण = काळोख वाढ".
Spot the difference
| Paksha | Moon |
|---|---|
| Shukla Paksha | Waxing, Amavasya to Pournima |
| Krishna Paksha | Waning, Pournima to Amavasya |
Practice questions
- 1What is a lunar month?
- 2What is a tithi?
- 3Which paksha is the waxing moon?
- 4Which paksha is the waning moon?
- 5How many days from new moon to full moon?
- 6How many pakshas are in a lunar month?
- 7After Pournima, which paksha begins?
- 8If a lunar month is 29 days, and Shukla Paksha is 15 days, how long is Krishna Paksha?
Show answers (try them yourself first)
- 1Time from one new moon to the next, 28–30 days.
- 2Each day of the lunar month.
- 3Shukla Paksha.
- 4Krishna Paksha.
- 5About 14–15 days.
- 6Two.
- 7Krishna Paksha.
- 829 − 15 = 14 days.
Quick revision
- Rotation gives day and night; revolution and inclined axis give seasons.
- 1 year = about 365 days 6 hours; leap year every 4 years.
- Moon phases: full moon, new moon, waxing, waning; lunar month = 28-30 days.