In basic astronomy, approximately how many days does the Moon take to complete one revolution around the Earth with respect to the stars?

Introduction / Context:
The motion of the Moon around the Earth is one of the most noticeable regular patterns in the sky. Understanding the approximate time the Moon takes to complete one revolution around the Earth helps in explaining phases of the Moon, tides and calendars. This question asks for the approximate period of revolution of the Moon with respect to distant stars, often referred to as the sidereal month.

Given Data / Assumptions:

• The Moon orbits the Earth in an approximately elliptical path.
• Two different time periods are often mentioned: the sidereal month and the synodic month.
• The question options include values close to the actual sidereal period.
• We assume the standard school level value taught for one revolution around the Earth.

Concept / Approach:
The sidereal month is the time taken by the Moon to complete one full orbit around the Earth relative to distant stars, and this period is about 27.3 days. The synodic month, which is the time from one new moon to the next, is slightly longer at about 29.5 days because the Earth Moon system also moves around the Sun. In many basic astronomy questions, when the phrase revolve around the Earth is used without extra detail, it refers to the sidereal period of about 27.3 days, which is the correct choice here.

Step-by-Step Solution:
Step 1: Recall that the Moon orbiting the Earth has a sidereal period of around 27.3 days. Step 2: Remember that 29.5 days corresponds to the lunar month between similar phases, not strictly the orbital period with respect to stars. Step 3: Compare the given options and locate 27.3 days among them. Step 4: Recognise that the other options 26.3, 28.3 and 29.2 are approximations that do not match the standard sidereal value. Step 5: Choose 27.3 days as the best answer consistent with standard textbook knowledge.

Verification / Alternative check:
Astronomy references and encyclopaedia entries commonly state that the Moon completes one revolution around the Earth relative to the fixed stars in about 27.3 days. They also mention a synodic period of about 29.5 days for the lunar phases. Diagrams showing the orbit of the Earth and Moon around the Sun are used to explain why these two periods differ. These sources consistently list 27.3 days as the orbital period relative to the stars, confirming the correctness of the chosen option.

Why Other Options Are Wrong:
Option a, 26.3 days, is significantly shorter than the accepted sidereal month and does not match standard data.

Option c, 28.3 days, is slightly longer than the sidereal period but still not the commonly quoted value.

Option d, 29.2 days, is closer to the synodic month but does not exactly represent the well known 29.5 day phase cycle, and the question refers to a revolution around the Earth in the basic sense.

Common Pitfalls:
A common confusion is between the sidereal and synodic months. Learners sometimes remember only one number and then apply it to every question. Another pitfall is to choose a rounded value that looks familiar without checking whether the question is about orbital revolution or phase cycle. Carefully reading the wording and recalling that 27.3 days is the orbital period helps avoid this mistake.

Final Answer:
The Moon takes approximately 27.3 days to complete one revolution around the Earth with respect to the stars.