How do eclipses occur?

Answer: Moon blocks or enters shadow

Moon blocks or enters shadow ✓ — Correct! Solar eclipse: Moon passes between Sun and Earth, blocking sunlight and casting a shadow on Earth. This only happens at new moon when all three align. Lunar eclipse: Earth passes between Sun and Moon, and Earth's shadow falls on the Moon. This only happens at full moon. We don't get eclipses every month because the Moon's orbit is tilted 5° to Earth's orbit, so alignment is rare.

Sun's light dims periodically — Wrong. The Sun's brightness is remarkably constant. It doesn't dim on a predictable schedule. Eclipses are caused by the Moon blocking the Sun's light (solar eclipse) or Earth's shadow falling on the Moon (lunar eclipse), not by changes in the Sun itself.

Earth's rotation causes them — Wrong. Earth's rotation causes day and night but doesn't cause eclipses. Eclipses require the Sun, Moon, and Earth to align in specific ways during the Moon's orbit around Earth. This alignment only happens occasionally, not daily as rotation would suggest.