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Line up the lamp, the globe and the Moon: why is there not an eclipse every month?
Solar & Lunar Eclipses lab · Last updated: 16 October 2026
You line up a lamp, a globe and a Moon to create solar and lunar eclipses. Then they solve a puzzle: if the Moon goes round Earth every month, why is there not an eclipse every month?
What you'll discover
- A solar eclipse happens when the Moon passes between the Sun and Earth and its shadow falls on Earth.
- A lunar eclipse happens when Earth passes between the Sun and Moon and Earth's shadow falls on the Moon.
- The Moon's orbit is tilted by about 5 degrees, so most months its shadow misses Earth and Earth's shadow misses it.
The science in plain words
An eclipse happens when the Sun, Earth and Moon line up and a shadow falls on one of them. In a solar eclipse the Moon passes between the Sun and Earth, and its shadow falls on part of Earth. People in the small, dark central shadow see a total eclipse, where the Moon covers the Sun completely. People in the wider, paler shadow see a partial eclipse. In a lunar eclipse Earth passes between the Sun and the Moon, and Earth's shadow falls on the Moon. Everyone on the night side of Earth can see it, and the Moon often turns a coppery red because Earth's atmosphere bends red sunlight into the shadow.
Solar eclipses can only happen at new Moon and lunar eclipses only at full Moon. So why not every month? The Moon's orbit is tilted by about 5 degrees compared with Earth's path round the Sun. Most months the Moon passes a little above or below the line between the Sun and Earth, so the shadows miss. Eclipses only happen when a new or full Moon falls near one of the two points where the Moon's orbit crosses Earth's. This lines up during eclipse seasons, about twice a year, so every year has at least two solar eclipses somewhere on Earth.
Never look directly at the Sun during a solar eclipse without certified eclipse glasses.
Where it fits
- India, NCERT: Class 7 science, Chapter 12: Earth, Moon, and the Sun
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-ESS1-1
Common questions
What is the difference between a solar and a lunar eclipse?
In a solar eclipse the Moon passes between the Sun and Earth and blocks the Sun's light, seen only from a narrow path on Earth. In a lunar eclipse Earth passes between the Sun and the Moon, and Earth's shadow darkens the Moon, visible from the whole night side.
Why is there not an eclipse every month?
The Moon's orbit is tilted by about 5 degrees to Earth's orbit round the Sun. Most months, at new and full Moon, the Moon passes slightly above or below the Sun and Earth line, so no shadow falls. Eclipses only happen when the line-up is close.
Why does the Moon turn red in a lunar eclipse?
Earth's atmosphere bends some sunlight into Earth's shadow. On the way, the air scatters away most of the blue light, the same effect that makes sunsets red. The remaining red and orange light reaches the Moon and gives it a coppery glow.
Related labs
- Moon Phases: A lamp, a globe and a Moon on real gravity: why does the Moon change shape?
- Earth's Seasons: Carry the globe round the lamp. Why is summer long and winter short?
- Solar System: A desk orrery run by real gravity: why does Mars take longer than Earth to go round?
See all earth and space labs or every Taz science lab.
Try it yourself
The Solar & Lunar Eclipses lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.