Question

seasons
across

1. season that is also called autumn
2. frozen water
3. fall starts during this month
4. the center of our solar system
5. in the beginning of fall and spring, this occurs when the earth is neither tilted towards or away from the sun
6. summer starts during this month
7. it is the coldest season

down

1. in the beginning of summer and winter, this occurs when the earth is tilted directly towards or away from the sun
2. season between spring and fall
3. winter starts during this month
4. snow melts during this season
5. they fall from trees during autumn
6. spring starts during this month
7. it falls from the sky during winter
8. it sits at an angle of 23.5 degree

Explanation:

The problem is a crossword puzzle about seasons, which involves knowledge of Earth's seasons, months, and astronomical concepts. The subfield of Natural Science, specifically Geography (or Astronomy, but Geography is more related to seasons' climate and Earth's tilt), applies here. The clues relate to seasonal changes, Earth's tilt, and months associated with seasons. For example, clue 1 (Down) about solstice (when Earth is tilted towards/away from sun), clue 2 (Down) about summer (season between spring and fall), etc. The answers are filled based on seasonal knowledge: e.g., 3 across is "Fall" (autumn), 14 across "June" (summer start), 15 across "Winter" (coldest season), 4 down "December" (winter start), 8 down "March" (spring start), 6 down "Spring" (snow melts), 7 down "Leaves" (fall from trees), 10 down "Snow" (falls in winter), 12 down "Sun" (solar system center), 13 across "Equinox" (equal day/night, when Earth not tilted towards/away), 1 across "Solstice" (when tilted), 2 down "Summer" (between spring and fall), 5 across "Ice" (frozen water), 9 across "September" (fall start).

Answer:

The filled crossword has answers like:
Across: 3. Fall, 5. Ice, 9. September, 12. Sun, 13. Equinox, 14. June, 15. Winter
Down: 1. Solstice, 2. Summer, 4. December, 6. Spring, 7. Leaves, 8. March, 10. Snow, 11. Tilt (assuming 11 down is about Earth's tilt, as 23.5 degrees)