4. Eclipses: When Sun, Earth & Moon Line Up

Once in a while the Sun, Earth, and Moon line up in a straight line, and one casts its shadow on another. That's an eclipse, and there are two kinds.

• Solar eclipse — the Moon passes between the Sun and Earth, so the Moon blocks the Sun and casts its shadow on part of Earth. This can only happen at new moon, and turns day briefly to twilight along a narrow path.
• Lunar eclipse — Earth passes between the Sun and Moon, so Earth's shadow falls on the Moon. This can only happen at full moon, and often turns the Moon a dim red.

So why don't we get an eclipse every month at every new and full moon? Because the Moon's orbit is tilted about 5° compared with Earth's orbit. Most months the Moon passes a little above or below the line, and the shadows miss. Only when the alignment is just right do we get an eclipse.

⚠️ Common misconception: eclipses are not rare because the Moon is far away — they're 'rare' because the Moon's tilted orbit usually carries its shadow just above or below the perfect line-up.

💡 Tip: Solar = Moon blocks Sun (new moon); Lunar = Earth's shadow on Moon (full moon). Tilt is why they're not monthly.