🌘 Solar and Lunar Eclipses

Sometimes the Sun goes dark in the middle of the day, and sometimes the Full Moon turns red. These are called eclipses! Let’s see how the Sun, Earth and Moon line up.

When an object gets in front of a light source, it casts a shadow behind it. The Sun is a big light source, so the shadow has two parts: the dark umbra, which gets no light at all, and the lighter penumbra, which gets a little light.

In a solar eclipse the order is Sun, Moon, Earth: the Moon is in the middle and its shadow falls on the Earth. This only happens at New Moon. The Moon’s shadow is small, so the eclipse can be seen from a narrow area only.

Places inside the Moon’s umbra see the Sun completely covered and the daytime sky goes dark: a total eclipse. Places in the penumbra see only part of the Sun covered: a partial eclipse.

In a lunar eclipse the order is Sun, Earth, Moon: the Earth is in the middle and its shadow falls on the Moon, so the Moon goes dark. This only happens at Full Moon. It can be seen from anywhere on Earth where it is night.

In a total lunar eclipse the Moon usually does not vanish. It looks reddish, the colour of copper. Sunlight bends as it passes through the Earth’s atmosphere, and the red light is the part that reaches the Moon most.

So why is there not an eclipse every month? Because the Moon’s orbit is tilted by about 5 degrees. Most months the Moon passes a little above or below the line-up and the shadow misses. For an eclipse, all three must be in exactly one line.

A common mistake: “In a solar eclipse the Earth is in the middle.” No! If the Earth is in the middle, it is a lunar eclipse. In a solar eclipse the Moon is in the middle and blocks the Sun.

Never look straight at the Sun, not even during an eclipse! Sunglasses and binoculars do not protect you and can damage your eyes for good. Use only special eclipse glasses or pinhole projection onto card.

Summary: in a solar eclipse the Moon is in the middle, at New Moon. In a lunar eclipse the Earth is in the middle, at Full Moon. Never look at the Sun with the naked eye! Now try it in Sky Laboratory!