Monday 27th September to Sunday 3rd October 2021
Between the constellations of Cassiopeia and Perseus you will find the Double Cluster which is a pair of open star clusters that can just be seen with the naked eye from a dark location. 

Stars in an open cluster are roughly all the same age as they were all originally formed from the same giant molecular cloud.


In the case of the Double Cluster, the stars are relative youngsters - only 13 million years old.  Compare this to another well-known open cluster we have looked at before - the Pleiades - the stars there are between 75 to 150 million years old!


Each half of the Double Cluster consists of a few hundred stars and they are actually moving towards us at a speed of approximately 24 miles per second.  Don't worry though as the clusters are 7,500 light years away and so it will be a very, very long time before they get close to us!


The Double Cluster is also known as Caldwell 14 - the Caldwell catalogue of deep sky objects was compiled for amateur astronomers by the late Sir Patrick Moore as a compliment to the Messier catalogue.


So when should you look for the Double Cluster?  The simple answer is "anytime" so long as it's dark (!) because the object is circumpolar.  This means that it is always above the horizon and will appear quite high in the night sky.  Just find the famous "W" shape of Cassiopeia first and then look across from there!



Sunday 19th September 2021
A friend of mine, Matt Lewis, took this amazing photograph one day before the Full Harvest Moon.
The jury is currently out on whether it is a "moonbow" or "sun dog", but either way it is a rare occurance!



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.  The image of Saturn's equinox below, 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.



Monday 13th to Sunday 19th September 2021
On Wednesday 15th at around 11.40pm, there is a good opportunity to observe the Great Red Spot on Jupiter with your telescope.  Jupiter will be located to the south, with Saturn and its amazing rings to the right of it and a setting Gibbous Moon further right again.

Jupiter spins very fast - a day and night, or in technical terms the sidereal period, only lasts ten hours.  This can make the Great Red Spot hard to see as very often, when you are observing the planet, the spot is round the wrong side!  You are actually looking at a huge storm that is at least 350 years old, with wind speeds approaching 300 miles per hour.  It is so enormous that a couple of Earths would fit inside it!


The first close-up view of the spot came from the Voyager 1 space probe that flew past Jupiter back in 1979.  After its fly-by, Voyager 1 headed away from the Solar System and in 2012 it left the Heliosphere which is defined as the furthest distance where things are influenced by our Sun.  Now the probe is approximately 14 billion kilometers away from Earth, travelling through the Interstellar Medium.


Because it is so far away, radio signals from the probe take the best part of a whole day to reach us.  It is estimated that by 2025, its little nuclear reactor that powers everything will be exhausted and we will then lose contact with it. 

Both Voyager 1 and its sister probe, Voyager 2, contain a golden record that contains sounds and photos of Earth - maybe one day it will be discovered by an alien civilisation!



Monday 6th to Sunday 12th September 2021

It's a week of visual challenges this time, starting with trying to spot a less than 1%-lit Crescent Moon on Monday 6th.  You'll need to be looking towards the east around 5.30am, before the Sun rises and the Moon will be close to the horizon.


If you don't fancy an early start, there is another opportunity on the evening of Tuesday 7th.  This time, the less than 1%-lit Moon sets in the west about half an hour after the Sun.


If you have binoculars or a small telescope, there is the chance to see an asteroid or minor planet called 2 Pallas.  It is known as one of the "Big Four" asteroids that were first-observed in the early 1800s.  Charles Messier spotted it twenty years earlier while tracking a comet, but he thought it was a star and moved on!


The asteroid has a mean diameter of just over 500km and is made of silicate material with little Iron, which gives it a blueish tint when observed.  It is believed to have a tiny 1km diameter moon orbiting around it.

The best evening to see the asteroid is Saturday 11th when it is at opposition, or in other words, its brightest at a magnitude of around +8.5.  Look to the south east from around 9pm and 2 Pallas will be located between the constellations of Pisces and Aquarius.

As the month progresses, each night 2 Pallas will appear slightly dimmer and closer to Aquarius.