- Earth's rotation on its axis → Daily Motion
| Key Point | Details |
|---|
| Rotation Period | 23 hours 56 minutes 4 seconds (mean sidereal day) |
| Direction | West to East |
| Linear / Tangential Rotation Speed | Maximum at Equator; zero linear speed at poles |
| Tilt of Earth's Axis | 23½° |
| Inclination of Earth's axis relative to orbital plane | 66½° |
| Speed at Equator | 1670 km/hr |
- Occurrence of Day and Night
- Change in direction of winds and ocean currents
- Rotation controls daily passage through tidal bulges; lunar/solar differential gravity generates tides.
⚡ Quick Recall
Axis Tilt = 23½° · Inclination to orbital plane = 66½° → (90° − 23½° = 66½°)
- Along with rotation, Earth's movement around the Sun → Annual Motion
| Key Point | Details |
|---|
| Revolution Period | ~365 days 6 hours 9 minutes 10 seconds (sidereal orbital period) |
| Path of Revolution | Anticlockwise, Elliptical path |
| Effects | Change in seasons • 6-month day and 6-month night at poles • Determination of year duration |
- Usually every 4 years; century years are leap years only if divisible by 400.
- Number of days in a year – 366 days
- February month – 29 days
- Due to the tilt of Earth's axis, days and nights become longer or shorter
| Position | Details |
|---|
| Minimum – Perihelion | Early January (~3 Jan): ~147 million km |
| Maximum – Aphelion | Early July (~4 July): ~152 million km |
📌 Apside Line
Line joining Perihelion and Aphelion
⚠ Exam Trap
Perihelion (nearest, 3 Jan) ≠ Aphelion (farthest, 4 July) — counter-intuitively Earth is closest to the Sun during Northern Hemisphere winter.
- Limits of Sun's Uttarayan (northward) and Dakshinayan (southward) movement
- Point of maximum difference in day-night duration
Summer Solstice
June solstice (~20–21 June); Karka Sankranti is a different, sidereal-zodiac date.
- Sun's rays fall vertically on Tropic of Cancer
- Longest day in Northern Hemisphere (21 June)
- Sun reaches its highest annual elevation at the North Pole.
- North Pole’s continuous daylight is already underway; roughly March equinox to September equinox.
Winter Solstice
December solstice (~21–22 December); Makara Sankranti is a different, sidereal-zodiac date.
- Sun's rays fall vertically on Tropic of Capricorn (22 December)
- Longest day in Southern Hemisphere
- South Pole’s continuous daylight is already underway; roughly September equinox to March equinox.
- Sun reaches its highest annual elevation at the South Pole.
- Midnight Sun in Norway – 21 June
- Shortest day in Northern Hemisphere – 22 December
- Summer Solstice in Southern Hemisphere – December
- Equinoxes: around 20–21 March and 22–23 September; day and night are almost equal.
⚡ Quick Recall
Summer Solstice = 21 June (N. Hemisphere longest day) · Winter Solstice = 22 December (N. Hemisphere shortest day)
- Sun's vertical rays fall on the Equator
- Almost equal day and night; exact equality is affected by refraction and the Sun’s apparent disk.
- No pole tilting towards the Sun
Vernal equinox (Northern Hemisphere): around 20–21 March
- Northern Hemisphere – Spring
- Southern Hemisphere – Autumn
Autumnal equinox (Northern Hemisphere): around 22–23 September
- Northern Hemisphere – Autumn
- Southern Hemisphere – Spring
⚠ Exam Trap
Vernal Equinox brings
Spring to the Northern Hemisphere but
Autumn to the Southern — the season label flips depending on hemisphere.
- Condition: Moon comes between Sun and Earth (Conjunction position)
- Time: New Moon (Amavasya)
Total Solar Eclipse
Full Sun covered
Partial Solar Eclipse
Partial Sun covered
Annular Solar Eclipse
Ring of Sun visible around Moon
- During totality, the faint corona becomes visible because the Moon blocks the bright photosphere.
- Diamond Ring phenomenon
- Dark Shadow: Umbra
- Light Shadow: Penumbra
⚡ Quick Recall
Umbra = Dark/Complete shadow · Penumbra = Light/Partial shadow
- Condition: Earth comes between Sun and Moon (Opposition position)
- Time: Full Moon (not on every full moon)
- Types: total, partial and penumbral
- Moon’s orbital plane is inclined about 5.1° to the ecliptic.
Super Moon
A full Moon near perigee, appearing somewhat larger and brighter
Blue Moon
Monthly definition: the second full Moon in one calendar month
Blood Moon
Red Moon during a total lunar eclipse; a tetrad is four consecutive total lunar eclipses about six lunar months apart.
- Sun, Moon, and Earth in one line – Syzygy
- Moon's nearest distance from Earth: Perigee
- Moon's farthest distance from Earth: Apogee
- Maximum 7 lunar and solar eclipses possible in a year
⚠ Exam Trap
Perigee (nearest) and Apogee (farthest) are often swapped with Perihelion/Aphelion (Sun-Earth distances) — Perigee/Apogee apply to the
Moon, Perihelion/Aphelion apply to the
Sun.
- Rise of sea water (Tide) and fall of sea water (Ebb)
Cause of Occurrence
- Gravitational pull of the Sun
- Gravitational pull of the Moon
- Inertial/centrifugal term of the Earth–Moon system’s motion about its barycentre
Theory
Progressive Wave Theory (William Whewell)
Spring Tide (Greatest Tidal Range)
- Sun, Earth, and Moon in a straight line
- Time – Full Moon and New Moon
Neap Tide (Smallest Tidal Range)
- Sun, Earth and Moon at right angles
- Time – 7th and 8th day of Krishna and Shukla Paksha
- Semidiurnal regime: successive high tides (or low tides) average about 12 hours 25 minutes apart.
- World's highest tide: Bay of Fundy → Nova Scotia (Canada)
- Generally 7-day gap between Spring and Neap tides
- Tidal Energy (in coastal areas), helpful in fisheries
⚡ Quick Recall
Spring Tide → Sun+Moon aligned (Full/New Moon) · Neap Tide → Sun+Moon at right angles