What is a solar eclipse?

A solar eclipse happens when the Sun, Moon and Earth are perfectly aligned. The Moon blocks light from the Sun and casts a shadow on Earth. The eclipse is visible to anybody within this shadow.

A solar eclipse can be either total, annular or partial. During a total solar eclipse, the Sun, Moon and Earth are perfectly aligned and the Moon covers the entire disc of the Sun. During an annular solar eclipse, the Sun's outer edge remains visible as a bright ring around the Moon. This happens because the size of the Moon in the sky changes as it moves along its elliptical orbit around Earth: the Moon appears smaller when it is farther away. During a partial solar eclipse, the Moon does not pass directly between the Sun and Earth, so only part of the Sun is covered by the Moon – it looks as though the Moon takes a bite from the Sun!

Solar eclipses occur about every 16 months and ‘totality’ (when the Sun is completely covered by the Moon) can last up to seven and a half minutes depending on the Earth-Moon-Sun geometry. Considering that the Moon takes 28 days to orbit Earth, why do we not see a solar eclipse every month? Because the orbit of the Moon around Earth is tilted, so the Moon often crosses above or below the imaginary line connecting the Sun and Earth. It is only when the Moon crosses this line that we see a solar eclipse.

Discover more about eclipses here.

[Image description: Graphic showing how the Moon (grey circle, centre) creates a solar eclipse by passing directly between the Earth (blue-green circle in the bottom right) and the Sun (yellow-orange circle in the top right). Lines trace the light rays travelling from the Sun's outer edges to Earth, outlining the areas of full shadow (highlighted dark purple) and partial shadow (highlighted light purple) cast by the Moon on Earth.]