The Moon is part of World and Physical Geography. Below are notes on 3 sub-topics, followed by practice MCQs from State PSC and UPSC papers.
Phases of the Moon and their Astronomical Significance
- Moon phases result from changing geometry of Sun-Earth-Moon system; Earth sees varying portions of the Moon's sunlit half.
- Lunar cycle (synodic month) is approximately 29.5 days.
- New Moon: Not visible from Earth; Moon is between Sun and Earth. Angle (Sun-MoonEarth) is ~0° (Moon is conjunct with Sun).
- Waxing Crescent: Small, growing sliver of light visible; occurs after New Moon.
- First Quarter: Half of the Moon's face visible from Earth is illuminated (right half in Northern Hemisphere); Moon is 90° from the Sun relative to Earth. Angle (Sun-EarthMoon) = 90°.
- Waxing Gibbous: More than half but less than fully illuminated, and growing; occurs after First Quarter.
- Full Moon: Entire face of Moon visible from Earth is illuminated; Earth is between Sun and Moon. Angle (Sun-Earth-Moon) = 180°.
- Waning Gibbous: More than half but less than fully illuminated, and shrinking; occurs after Full Moon.
- Last Quarter (Third Quarter): Half of the Moon's face visible from Earth is illuminated (left half in Northern Hemisphere); Moon is 90° from the Sun relative to Earth. Angle (Sun-Earth-Moon) = 90°.
- Waning Crescent: Small, shrinking sliver of light visible; occurs after Last Quarter, before New Moon.
13. Asteroids
Phenomena: Supermoon, Blue Moon, and Blood Moon
- Blue Moon: Occurs when a second full moon appears within a single calendar month.
- Supermoon: Occurs when a full moon coincides with its closest approach to Earth (perigee) in its elliptical orbit, making it appear larger and brighter.
- Blood Moon: Refers to the reddish-orange appearance of the Moon during a total lunar eclipse. This happens when Earth is directly between the Sun and Moon, and sunlight filtered through Earth's atmosphere reaches the Moon.
- Coincidence: It is rare but possible for a Blue Moon, a Supermoon, and a total lunar eclipse (Blood Moon) to occur on the same day (e.g., January 31, 2018).
Physical Characteristics and Internal Structure
- Earth's only natural satellite.
Practice MCQs: The Moon
Phases of the Moon and their Astronomical Significance
Observe the following diagram and state which of the following alphabets indicate the gibbous phase of the moon ?
Asked in: MPSC CS Prelims 2023
- B and H
- C and G
- D and F
- E and A
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Answer: B. C and G
Moon phases are determined by the relative positions of the Sun, Earth, and Moon. As the Moon orbits the Earth, the portion of the Moon illuminated by the Sun that is visible from Earth changes, creating the different phases (New Moon, Crescent, Quarter, Gibbous, Full Moon). Gibbous means more than half-illuminated.
Phenomena: Supermoon, Blue Moon, and Blood Moon
The phenomenon of Blue Moon is ________.
Asked in: GPSC Prelims CSP 2 2021
- If a second full moon appears in a calendar month
- If the second full moon appears in two consec‐ utive months in a calendar year
- If full moon appears thrice in a calendar month
- None of the above
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Answer: A. If a second full moon appears in a calendar month
- A full moon occurs roughly every 29.5 days (synodic period). - A calendar month is typically 30 or 31 days long. - The occurrence of a second full moon in a month is relatively rare, giving rise to the phrase "once in a blue moon".
On January 31, 2018, a rare 'Blue Moon' event was experienced in large parts of the globe. In that context consider the following statements:
Asked in: MPSC CS Prelims 2019
- Only a
- Only a and b
- Only b and c
- Only a and c
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Answer: A. Only a
It was a rare moment as a blue moon, a super moon and a total lunar eclipse fell on the same day. When two full moons appear in the same calendar month, the second is termed as 'Super moon'. When the full moon is at the closest point of its orbit to the Earth it is termed as 'Blue moon'. The correct statement/s is/are : - Statement 2 incorrectly defines a Super Moon. A Super Moon occurs when a new or full moon is at its closest point to Earth in its elliptical orbit (perigee). The phenomenon described in statement 2 (second full moon in a month) is the definition of a Blue Moon. - Statement 3 incorrectly defines a Blue Moon. The phenomenon described in statement 3 (full moon at the closest point of orbit) is the definition of a Super Moon.
Physical Characteristics and Internal Structure
The moon is a
Asked in: Agriculture Development Officer(ADO) 2017
- Comet
- Satellite
- Star
- Planet
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Answer: B. Satellite
A satellite is an object that orbits a larger celestial body. Natural satellites are celestial bodies that orbit planets or dwarf planets. The region between the orbits of Mars and Jupiter is known as the Asteroid Belt. This belt is populated by a large number of rocky bodies of various sizes, ranging from dust grains to dwarf planets, which are called asteroids.
Consider the following statements regarding asteroids: I. Asteroids are rocky debris of varying sizes orbiting the Sun. II. Most of the asteroids are small but some have diameter as large as 1000 km. III. The orbit of asteroids lies between the orbits of Jupiter and Saturn. Of these statements:
Asked in: UPPCS Prelims 1998
- I, II and III are correct
- II and III are correct
- I and II are correct
- I and III are correct
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Answer: C. I and II are correct
- Statement I is correct: Asteroids are indeed rocky, metallic, or icy bodies of varying sizes that orbit the Sun, primarily remnants from the early solar system. - Statement II is correct: While most asteroids are small, the largest ones like Ceres, Pallas, Vesta, and Hygiea have diameters ranging from over 400 km to nearly 940 km (for Ceres), which makes "as large as 1000 km" a reasonable statement for the largest known ones at the time this question might have been framed. Ceres is sometimes classified as a dwarf planet. - Statement III is incorrect: The main asteroid belt, where most asteroids are found, is located between the orbits of Mars and Jupiter, not Jupiter and Saturn.