Harvest moon is extra big and extra bright
THE harvest moon earlier this month was an impressive sight in lovely colourful skies on clear, calm evenings.
Since our planet has just one natural satellite, our solitary moon is nameless. To us it is just ‘ the moon’. Locked into Earth’s gravity, it orbits us once a month, or to be precise every 29 days 12 hours and 44 minutes calculated with respect to the sun. Each orbit begins with the new moon when its face appears black as it is not illuminated by the sun.
As the moon brightens, light enters on the right hand side and its face gradually illuminates, waxing from a crescent to a first quarter to gibbous and on to a full moon when there is a complete circle of light. The situation then reverses as the light departs, emptying to the left through waning gibbous, last quarter and waning crescent to bring us back to the new moon again.
Earth, moon and sun are in line twice each month. On the occasion when the moon is in the middle of the straight line its side facing us is obviously not illuminated by the sun. Consequently, it appears dark and is the new moon phase of the lunar cycle.
When Earth is in the middle, the sun shines past us and lights up the whole face of our orbiting natural satellite producing the full moon. One full moon occurs each month and each of the twelve full moons that occur each year has been given a name. The September full moon is the harvest moon.
The harvest moon is extra big, extra bright and extra orange and got its name from the fact that in days of yore its brightness immediately after sunset lengthened the day for farmers harvesting crops before autumn weather turned against them.
Why the harvest moon is extra big and extra bright is due to the moon’s orbit being slightly elliptical rather than being perfectly circular. At this time of year, the moon swings particularly close to us so it looks noticeable bigger and brighter.
The harvest moon is also different in that it rises close to the horizon making it look bigger and more orange. When the moon rises high in the sky at other times of the year, we have nothing close by to judge its size against so it appears smaller and it is paler due to the way the different thickness of atmosphere scatters the light.