IN September, there will be a total eclipse of the Harvest Moon. The eclipse is unusual in one very special way; it will occur when the Moon is at its closest point to the Earth this year. This means it will be a monster moon and will appear to be 13 per cent larger than the last eclipse on April 4 this year.

Some eclipses are partial, but this eclipse will be the fourth consecutive total eclipse of the Moon which is referred to as a ‘Lunar Tetrad’. They are rare events, running on long and complicated cycles. There were only two Tetrads in the 20th century, in 1949-50 and 1967-68, and before these dates the previous tetrad occurred in 1493-1494. The first three total eclipses in this lunar tetrad occurred on April 15 2014, October 8 2014, and April 4 2015. This fourth eclipse is sometimes called the ‘Blood Moon’.

Some people believe that this tetrad has special significance because the eclipses coincide with important Jewish festivals. The two April lunar eclipses in 2014 and 2015 occurred at the same time as Passover, while the October and September eclipses occur during the Feast of Tabernacle. This, they suggest, is connected to a biblical prophecy of the end of the world.

Will the prophecy come true this time?

In September the first hint of autumn can be seen in the sky, with the Pleiades, or seven sisters, appearing low in the East. This is the finest open cluster of stars in the sky. The appearance of the Pleiades before midnight marks the approach of colder nights.

Ursa Major or the Plough is now comparatively low with the ‘W’ of Cassiopeia becoming much higher.

The Square of Pegasus is high up in the South East; Deneb in the summer triangle is almost overhead with Vega beginning to drop westwards. Altair remains prominent, but Antares has now set.

What’s up in the solar system?

The Planets in September

We still only have Saturn on view this month, which can be seen low in the South and will set by 10.00 pm. The other planets are all very close to the Sun and difficult to see.

Meteor Showers

There are no major meteor showers this month

Phases of the Moon for September

Last Quarter 5th, New Moon 13th, First Quarter 21st, Full Moon 28th

Eclipse of the Moon

This month’s eclipse of the Moon occurs on the morning of September 28. An eclipse of the Moon occurs when the Moon is full. Between 03.11 and 04.23 the Moon will change colour. The Earth casts a shadow in space about 860,000 miles long, which is about three times the distance of the Moon from the Earth. On the diagram, ‘umbra’ is Latin for shadow, and ‘pen’, as in penumbra, is from ‘paene’, meaning almost. When the Moon passes into the centre of the umbra, it will change from its normal white colour to dark red. This is a Lunar Eclipse and it can last for about an hour and three quarters.

The Moon does not make its own light; it reflects light from the Sun. Moonlight is simply reflected sunlight.

The reason that the Moon does not completely disappear is that light from the Sun passes through the Earth’s atmosphere which acts a little bit like a lens and causes the light to be refracted, or bent, before it reaches the surface of the Moon, thus causing it to change colour.

The full moon this month has been called the Harvest Moon since mediaeval times. At this time of year as the Sun sets the Moon rises, which in past times allowed farmers to harvest their crops through the night using the light from the Moon.

The next meeting of the Earby Astronomical Society will be on Friday, October 2 from 7.30pm to 9pm at All Saints’ Church, Earby. The speaker will be Martin Lunn MBE FRAS, Earby Astronomical Society, and the title of the talk will be The Autumn Sky.