A close-up image of a total solar eclipse. The sky is black and a white corona streams out from behind the Moon. It is elongated at 10 o'clock and 4 o'clock.

A total solar eclipse reveals the Sun's faint corona.

What is a solar eclipse?

The Sun, Moon and Earth form one of the most spectacular astronomical events that can be seen, turning day into night.

  • 19 September 2006 | Updated 14 October 2011

A total solar eclipse is one of the most spectacular astronomical events. It occurs when the Moon passes between the Sun and the Earth.

For a short period of time, the Sun is completely blocked out by the Moon, when viewed from the Earth.

Day briefly turns into night, causing temperatures to drop, birds begin to roost and many animals become confused. 

Celestial mechanics

The Moon orbits our planet once every 29 and a half days. If you looked at our solar system from above the Earth, you would see that during its orbit the Moon passes between Earth and the Sun.

If you viewed the solar system from the side, however, you would see that the Moon's orbit is not always in line with the Sun and the Earth. That's why an eclipse doesn't happen every month.

Approximately once in every seven orbits the Earth, Moon, and Sun line up, and a solar eclipse occurs.

The diameter of the Sun is approximately 400 times larger than that of the Moon, but when you look at the Sun or the Moon from Earth, they appear to be the same size. This is because the Sun is almost 400 times farther away. A strange cosmic coincidence.

Shadow of the Moon

Not every solar eclipse is total. If the Sun and the Moon don't line up perfectly, then only a fraction of the Sun is covered. This is called a partial solar eclipse.

A photo of a partial solar eclipse setting behind the Parkes radio telescope.

A partial solar eclipse occurs when the Moon does not cover all of the Sun.

The area experiencing a total solar eclipse will be in darkness, because the Moon blocks any sunlight from reaching the Earth.

This temporary darkness is known as the umbral shadow, and it's usually a path less than 100 kilometres in width.

Because the Moon and the Earth are always in motion, the shadow also moves. That's why a total solar eclipse doesn't last forever. In fact, viewed from any one place, it is never longer than seven minutes.

People watching in an area outside but close to the umbral shadow will see a partial solar eclipse. This is known as the penumbral shadow, and is much larger than an umbral shadow. Partial solar eclipses can last for over an hour.

Find out more about History of total solar eclipses.