Adrian Dening's Stars Over Somerset

Wednesday, 15 September 2021 17:00

Monday 20th to Sunday 26th September 2021

Just after sunset on Monday 20th September, a Full Moon rises in the east. This will be the closest Full Moon to the autumnal equinox so it is called a Harvest Moon.

There are two equinoxes during the year, when we are sideways on to Sun during our journey around it and so the hours of daylight and night are equal. In other words, precisely half of the Earth's surface is illuminated by the Sun. The autumnal equinox actually occurs on Wednesday 22nd September and in the northern hemisphere it marks the start of our autumn season.

Six months later, we will have the vernal equinox. This name is derived from the Latin word for spring which is "ver".

The Earth is tilted 23.5 degrees - north and south are not straight up and down! Any planet that has a tilted axis will have equinoxes. I have posted an image of Saturn's equinox. This image, courtesy of NASA and the Jet Propulsion Laboratory shows the effect very clearly.

There are two excellent opportunities to spot the International Space Station on Thursday 23rd at 8.46pm and Friday 24th at 7.59pm. In both cases, the ISS will appear over the horizon in the west and spend about five minutes passing almost directly overhead, before disappearing to the east.

Screenshot courtesy of Stellarium
Copyright Adrian Dening and Radio Ninesprings 2021