Although a Full Moon occurs every month, a total lunar eclipse does NOT occur every Full Moon day. Why?

Although a Full Moon occurs every month, a total lunar eclipse does NOT occur every Full Moon day. Why?
  1. The Moon's atmosphere blocks Earth's shadow.
  2. The Moon's orbital plane is tilted at about 5 degrees relative to Earth's orbital plane.
  3. The speed of Earth's revolution varies greatly every month.
  4. The Sun's distance from Earth changes drastically during Full Moon.

Solution

Because the Moon's orbit is tilted at about $5^\circ$ to Earth's orbital plane, the Sun, Earth, and Moon do not align in an exact straight line on every Full Moon.

Asked in: Homi Bhabha Practice

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