Make an eclipse shadow model
Get to know the interaction between the Moon and Earth during eclipses
Here on Earth, when the Sun shines on an object, it casts a shadow. But those shadows aren’t limited to the terrestrial surface: the Moon and Earth cast shadows into space too, and as the two bodies interact with those shadows, it creates lunar and solar eclipses.
A lunar eclipse occurs when the Moon passes into Earth’s shadow. This can only occur during a full Moon, when the Moon is on the opposite side of Earth from the Sun. There are two parts to Earth’s shadow; the darker umbra and a slightly brighter penumbra. If the Moon passes fully into the umbral shadow, a total lunar eclipse occurs and the Moon will turn a reddish brown colour. Because Earth’s shadow is so huge, a total lunar eclipse takes place over several hours. If the Moon only passes part way into the shadow we get a partial lunar eclipse.
Cast into shadow
A solar eclipse occurs when the Moon passes between the Sun and Earth. This can only occur during a new Moon. The Moon is 400 times smaller than the Sun, but the Sun is 400 times further away, so during totality the Moon perfectly covers the Sun. This allows us to view the Sun’s corona, which is too faint to observe at any other time. As the Moon passes in front of the Sun, it casts a small shadow that races across Earth’s surface at between 1,600 and 8,000 kilometres per hour. The Moon’s shadow is also made up of an umbra and penumbra. If you are in the path of the umbral shadow you will experience totality, but this only lasts for a couple of minutes.
Eclipses don’t occur every month because the Moon’s orbit is tilted. From any specific location total lunar eclipses are visible about every 2.5 years; the next one from the UK is on 16 May 2022. Partial lunar eclipses are more frequent and the next one is on 19 November 2021. Total solar eclipses, however, are much rarer. The next one visible from the UK isn’t until 23 September 2090, but we do get to see a partial solar eclipse on 10 June 2021.
Because eclipses can’t be viewed in person that often, it is helpful to have a model that you can use to demonstrate how they work. The model also allows us to get the wider view of how eclipses look from space, rather than just from Earth’s surface.
This model is simple to make and is a fun family project. It can be used to demonstrate both lunar and solar eclipses, and it shows the umbral and penumbral shadows in both cases. One thing to note is that although the relative size of Earth and Moon in our model is roughly correct, the distances are not to scale. If they were, the Moon would need to be 2.6m from Earth, and the lamp used as the Sun would need to be 1.02km away and have a diameter of 9.5m.
All rather impractical at home, so we’ve gone for a sensible size, which will still show the theory well.