Question

After the period of how many days half-moon can be seen?
A. ${\text{7 or 22 days}}$
B. ${\text{1 or 30 days}}$
C. ${\text{15 days}}$
D. ${\text{10 or 17 days}}$

Answer 1

Hint: The moon phase or lunar phase is the portion of the moon which is illuminated by sunlight as seen from the earth. We can see a half moon phase a week later and a full moon is visible after 15 days. The cycle repeats after this and we can again see a half moon one after the full moon phase.

Complete step by step answer:
Let us first discuss the moon phases.
The moon phase or lunar phase is the portion of the moon which is illuminated by sunlight as seen from the earth. There are mainly 8 phases in order, new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter and waning crescent. This is shown in the figure.

As seen from the figure, we can see a half moon phase a week later and a full moon is visible after 15 days. The cycle repeats after this and we can again see a half moon one after the full moon phase i.e. the 22nd day after the new moon.
Therefore, after the period of 7 or 22 days, a half-moon can be seen.
Hence, option A is correct.

Note: The different Moon phases are seen the same from any part of the earth, both in the Northern and Southern Hemispheres. The percentage of the Moon which is illuminated no matter is independent of our position on the earth. However, the shape of Waxing Crescent Moon depends on the time, the date, our location on the earth, and the position of the moon in the sky and can be seen like a banana, a boat, or even as an umbrella.