Lunar day — time between successive transits of the Moon across the local meridian What is the approximate time interval between successive upper transits (meridian passages) of the Moon as observed from the same place on Earth?

Introduction / Context:
The Moon’s apparent daily motion combines Earth’s rotation and the Moon’s own orbital motion around Earth. As a result, the time between the Moon’s successive meridian transits (the “lunar day”) is longer than a mean solar day. This fact is essential for planning astronomical observations, tide predictions, and instrument checks that depend on the Moon’s position.

Given Data / Assumptions:

• Mean solar day ≈ 24 hours.
• The Moon orbits eastward relative to the stars.
• We seek the interval between two successive meridian passages (upper transits) of the Moon.

Concept / Approach:
Because the Moon moves eastward about 13° per day relative to the stars, Earth must rotate slightly more than 360° for the Moon to return to the local meridian. This adds roughly 50 minutes to the 24-hour solar day, making the mean interval about 24 h 50 min. This is analogous to the difference between a solar and a sidereal day, but larger because the Moon’s orbital angular speed (relative to the stars) is much greater than the Sun’s apparent motion.

Step-by-Step Solution:

Verification / Alternative check:
Astronomical almanacs list lunar transit intervals around 24 h 50 min on average, with variations due to orbital eccentricity and declination effects.

Why Other Options Are Wrong:

• 23 h 50 min or 24 h 10 min: too short; would imply westward lunar motion.
• 20 h 25 min or 23 h 25 min: far from the mean lunar day; physically unrealistic for average conditions.

Common Pitfalls:
Confusing sidereal day (≈ 23 h 56 m) with the lunar day; forgetting the Moon’s significant eastward drift each day.

Final Answer:
24 hours 50 minutes