Keeping Time with the Skies Class 8 Notes

Keeping Time with the Skies Class 8 Notes

Keeping Time with the Skies Class 8 Notes

1. Moon: A natural satellite that orbits the Earth.
2. Phases of the Moon: The different appearances of the Moon as seen from Earth.
3. Full Moon: The phase when the entire face of the Moon is illuminated by the Sun.
4. New Moon: The phase when the Moon is not visible from Earth because it is positioned between the Earth and the Sun.
5. Waxing: The period when the visible portion of the Moon is increasing, moving from new Moon to full Moon.
6. Waning: The period when the visible portion of the Moon is decreasing, moving from full Moon to new Moon.
7. Crescent Moon: A phase of the Moon where less than half of the Moon is illuminated, appearing as a thin arc.
8. Gibbous Moon: A phase of the Moon where more than half, but not all, of the Moon is illuminated.
9. Lunar Eclipse: An event that occurs when the Earth passes between the Sun and the Moon, causing the Earth's shadow to fall on the Moon.
10. Solar Eclipse: An event that occurs when the Moon passes between the Earth and the Sun, blocking the Sun's light.
11. Orbit: The path that one celestial body takes around another due to gravitational forces.
12. Tilt of the Moon's Orbit: The slight angle at which the Moon's orbit is inclined relative to the Earth's orbit around the Sun.
13. Positional Astronomy: The branch of astronomy that deals with the positions and movements of celestial bodies.
14. Moonrise: The time at which the Moon appears above the horizon in the sky.
15. Duration of day: The length of time from one sunrise to the next.
16. Shadow: The dark shape produced when an object blocks light.
17. Eclipses: The phenomena that occur due to the alignment of the Earth, Moon, and Sun.

1. Types of Calendars

(a) Lunar Calendars

1. Definition: Based on the Moon's phases
2. Characteristics: 12 lunar months =354 days

Limitations: Shortfall of nearly 11 days compared to the solar year

(b) Luni-Solar Calendars

1. Definition: Combines lunar months with solar year adjustments
2. Example: Adjustments made every 2-3 years to align with seasons

2. Solar Year and Seasons:

Definition: Earth's revolution around the Sun takes approximately 365.25 days

Seasonal Change:

1. Uttarayana: Sun's northward movement (December to June)
2. Dakshinayana: Sun's southward movement (June to December)

Solstices and Equinoxes:

1. Dates: June 21 (Summer Solstice), December 21 (Winter Solstice)
2. Observations: Sun rises in different positions during these events

3. Historical Observations:

1. Ancient civilizations tracking celestial movements
2. Use of stars and constellations for timekeeping
3. Example: Capricorn and Cancer in ancient Indian texts

4. Phases of the Moon:

1. Cycle Duration: Approximately 29.5 days
2. Observational Activity: Tracking the Moon's appearance over a month
3. Importance of lunar phases in defining months

5. Artificial Satellites:

1. Definition: Man-made objects orbiting Earth
2. Functions: Communication, navigation, weather monitoring, scientific research
3. Example: ISRO's satellites (Cartosat, AstroSat, Chandrayaan missions)