Note4Students
From UPSC perspective, the following things are important :
Prelims level: Eclipses
Mains level: Read the attached story
Central Idea
- While Eclipses are intriguing, one might wonder why eclipses do not occur with every new and full moon.
What are Eclipses?
- Eclipses are astronomical events that occur when the sun, moon, and Earth align in specific ways.
- There are two primary types of eclipses: solar and lunar.
- A solar eclipse happens when the moon comes between the sun and Earth during a new moon, blocking out the sun’s light.
- Conversely, a lunar eclipse occurs when the Earth is positioned between the sun and the moon during a full moon, casting a shadow on the moon.
Visit this page to read more about Eclipses:
Why is there no eclipse every full and new moon?
Ans. Moon’s Unique Orbit
- Moon’s Path: The moon orbits around Earth, completing one orbit roughly every month.
- Ecliptic Plane: In an ideal scenario, if the moon’s orbit matched Earth’s orbital plane, called the ecliptic, we would witness a solar eclipse during every new moon and a lunar eclipse during every full moon.
- Moon’s Inclination: However, the moon’s orbit is inclined at an angle of about 5 degrees to Earth’s orbital plane, causing irregular eclipse patterns.
Role of Lunar Nodes
- Lunar Nodes: The moon’s orbit intersects Earth’s orbital plane at specific points known as nodes, categorized as ascending or descending nodes depending on the moon’s orbital direction.
- Eclipse Occurrence: Eclipses happen when a full or new moon closely aligns with one of these nodes, ensuring the sun, moon, and Earth are in alignment.
Eclipse Pairs and Seasons
- Eclipse Pairs: Solar and lunar eclipses typically occur in pairs, with one following the other within a two-week period.
- Eclipse Seasons: Eclipse seasons, lasting around 34 to 35 days, usually feature two eclipses – one solar and one lunar. Occasionally, three eclipses may occur in a single season.
- Frequency: Contrary to common perception, there are more eclipses than expected, with the 21st century witnessing 224 solar eclipses and 230 lunar eclipses.
Understanding the Lunar Nodes and Eclipses
- Eclipse Seasons: Eclipse seasons take place approximately every 173 days when the lunar nodes precisely align with the Earth and the sun.
- Moon’s Progression: The moon’s phases shift about 30 degrees along the zodiac every month concerning the nodes.
- Future Eclipses: After a pair of eclipses, the next pair usually occurs nearly 6 calendar months later.
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