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Cause and Effect — From Sky to Calendar
How the Sky Keeps Our Time
Sky bodies move in regular cycles
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Moon's phases
Give the month; the Sun gives the day.
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Earth's orbit
Gives the year and the seasons.
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Lunar, solar, and luni-solar calendars
Mind Map
Time & the Skies
Cycles of Moon, Sun, and Earth
11.1
Moon's Appearance
Phases come from seeing different amounts of the lit Moon.
11.2
Calendars
Lunar, solar, and luni-solar calendars from sky cycles.
11.3
Festivals
Festival dates follow the Moon's phases or the Sun's position.
11.4
Satellites
Artificial satellites help us and leave space debris behind.
Key Terms and Definitions
- Phases of the Moon
- The changing shapes of the Moon's bright portion seen from Earth day to day.
- Waxing period
- When the Moon's bright part increases (Shukla Paksha).
- Waning period
- When the Moon's bright part decreases (Krishna Paksha).
- Full Moon (Purnima)
- The day the Moon appears as a full bright circle.
- New Moon (Amavasya)
- The day the Moon is not visible.
- Gibbous phase
- When more than half the Moon's lit portion is seen.
- Crescent phase
- When less than half the Moon's lit portion is seen.
- Mean solar day
- The average 24-hour time between the Sun's highest points on consecutive days.
- Month
- A time unit from the Moon's phase cycle of about 29.5 days.
- Solar year
- The time the Earth takes to orbit the Sun, about 365 and a quarter days.
- Lunar calendar
- A calendar of 12 lunar months (about 354 days), based on the Moon.
- Solar calendar
- A 365-day calendar kept in step with the seasons, like the Gregorian.
- Leap year
- A year with an extra day to adjust for the extra quarter day.
- Luni-solar calendar
- A Moon-based calendar adjusted to the seasons with an extra month.
- Adhika Maasa
- The extra month added to keep lunar and solar cycles in step.
- Artificial satellite
- A human-made object launched to orbit the Earth for many uses.
