Solar and lunar eclipses

What the -- That is a solar eclipse... ... I always wanted to see that. A solar eclipse. The moon is passing exactly in between the earth and the sun, so that all three form a straight line. The shadow of the moon falls on the earth, and we can't see the sun.

This is a total solar eclipse. It only lasts for a short while. Seven and a half minutes, at the most. That's because the moon's shadow is narrow, and only covers a tiny part of the earth. If you happen to be standing right there, you'll see the sun completely blocked out.

This diagram isn't to scale. In reality, the sun is much larger compared to the Earth, and further away, too. But the diagram helps to show that the sun and moon appear to be the same size, seen from Earth, even though the sun is a lot bigger. This is because it's also a lot further away. That's why the moon covers the view of the sun almost perfectly.

The moon makes its way around the Earth, and its shadow sweeps along the Earth's surface. Even if you are not in a place where the sun is totally covered by the moon, chances are that you can still see the moon cover a part of the sun. Here, the moon only covers a part of the sun, leaving you in the partial shadow, the penumbra. Because the moon is a long way from the Earth, the penumbra covers a much larger area than the core of the shadow, the umbra. If you are in the penumbra, you see a partial solar eclipse. -- The moon keeps orbiting the earth, and eventually it passes over the other side of the earth.

And here, another kind of eclipse can happen. This time, if the three celestial bodies line up perfectly, it's the Earth's shadow that falls on the moon. This is a lunar eclipse. The Earth's shadow is large, and the moon must travel quite a distance to get out of it. You are much more likely to see a lunar eclipse than a solar one, since the lunar eclipse can be seen from any place on Earth facing the moon.

And a lunar eclipse lasts for several hours; much longer than a solar eclipse does. -- Here is the Earth's orbit around the sun. Imagine its orbit forming a disc, which we call the ecliptic. Here is the moon's orbit around the earth. The orbit of the moon is tilted, compared to the ecliptic. Approximately five degrees.

For an eclipse to be possible, two things must happen: Firstly, the moon must be at that point in its orbit, where it crosses the ecliptic. This happens twice during each revolution of the moon around the Earth. These two points are called the 'lunar nodes'. Secondly, one of these lunar nodes must form a straight line with the Earth and the sun. Most of the year eclipses are not possible, but during two periods every year we have an eclipse season.

When the moon is at a lunar node, at the same time as being in line with the sun and the earth, it's a solar eclipse! Which you can see... if you are in the right place. There may be as many as seven eclipses every year. Some lunar, some solar.

Some are full and some are partial. And if you're lucky you might see one. Cool! Let's stay here for the next eclipse. This is a perfect place to watch it.

You'll need patience then. -- The solar eclipse occurs at different places every time. -- Won't be back here for several hundred years. --