- The new moon is when the dark half of the moon faces the earth
- The dark half of the moon is not visible
- Hence, new moon is when the moon cannot be seen

- New moon is when the moon cannot be seen
- A new moon is a kind of phase of the moon
- A student cannot observe the moon in the clear night sky on feburary 21
- Hence, the student observes a new moon phase on feburary 21

- The student observes a new moon phase on feburary 21
- A moon phase occurs 28 days after the last time it occurred
- So, the next new moon will occur 28 days after feburary 21

- The next new moon will occur 28 days after feburary 21
- 28 days after feburary 21 is march 21
- Therefore, the next new moon will occur on march 21

So, the next new moon will occur on march 21
Question: On February 21, a student observes that the Moon cannot be seen in the clear night sky. On what date will the student not be able to see the Moon again in the clear night sky?
Context: - A new moon is a kind of phase of the moon 
- A student cannot observe the moon in the clear night sky on feburary 21 
- A moon phase occurs 28 days after the last time it occurred 
- The new moon is when the dark half of the moon faces the earth 
- The dark half of the moon is not visible 
- 28 days after feburary 21 is march 21