IT ONLY happens twice a year - but the equinox produces some fantastic imagery.

Yesterday morning the stunning effects of the autumn equinox could be seen across the waters of Buttermere in the Lake District.

The equinox in September marks the end of summer and the start of the autumn, while the spring equinox marks the beginning of spring.

David Ramshaw, of the Border Astronomical Society, said: “We have seasons on the earth because the earth is tilted on its axis (at about 23 degrees) as it orbits round the sun.

“The path that the sun traces through the sky is called the ecliptic and the autumnal equinox occurs when the sun crosses the Celestial Equator on September 22-23 each year.

“At this time we have 12 hours of daylight and 12 hours of darkness.

“For the next six months the sun’s path (the ecliptic), for those of us in the northern hemisphere, will be below the celestial equator and we will get shorter days and longer nights until March 23 when once more the sun crosses the celestial equator when we have 12 hours of daylight and 12 hours of darkness.

“For the six months after that the sun’s path through the sky is above the celestial equator and we then get longer days and shorter nights until 21st June, midsummer’s day. The celestial equator is an imaginary circle around the sky in line with our geographical equator.

“The opposite happens in the southern hemisphere: as our summer ends and autumn begins for us, in Australia their winter is ending and spring beginning.”

Mr Ramshaw has witnessed the equinox for himself, but said: “It is just a particular point in the year. The thing of importance is that it marks the start of autumn.”

Other key dates in the astronomical calendar:

The solstice - also taking place twice a year, in summer and winter, is the day with the longest period of sunlight, while the winter solstice is the day with the shortest period.

The equilux - when day and night are equal and occurs a few days before the spring equinox, and a few days after the autumn equinox.

The solar eclipse - happens every 14 months on average, when the moon and the sun are at the precise size and distance to appear directly aligned from earth. The last solar eclipse took place on July 2.