The Harvest Moon – a golden globe to welcome the autumn

For those of us in the northern hemisphere, it is the week of the Harvest Moon. This is defined as the full moon nearest to the autumnal equinox, which took place last week on 22 September. In the southern hemisphere, the Harvest Moon takes place in March or April, close to the March equinox.

This week the full moon takes place on 1 October 22:05 BST, but because the moon rises soon after sunset on several days close to the equinox, it often seems as if a full moon appears on a number of consecutive days. According to tradition, this extra illumination made it easier for farmers to gather in their crops.

The Harvest Moon – as all full moons – often looks orange when it is near the horizon. This is because its light is passing through more layers of atmosphere than when it is overhead. Since the atmosphere preferentially scatters blue light more than red light (which is why the sky is blue), the more layers of atmosphere the moonlight has to pass through, the redder it will appear.