Monday 25th to Sunday 31st October 2021

On the morning of Monday 25th October, Mercury is at its greatest elongation or in other words the planet appears to be the furthest it gets from the Sun.  If you look just south of east from about 6.15am, Mercury will have risen above the horizon.  To the left of Mercury, slightly north of east will be the bright star Arcturus.


Please remember that if you are using binoculars or a telescope, make sure you don't catch even a glimpse of the Sun rising an hour later.


Moving towards the end of the week and the evening shift, on Friday 29th a "Last Quarter" Moon will have risen above the horizon in the east by 1am.  If you look slightly down and to the right of the Moon, have a go at spotting the Beehive Cluster - M44 in the Messier Catalogue.


The Beehive Cluster is the closest open star cluster to the Earth and it was first observed by Galileo back in 1609.  He managed to resolve 40 stars with his early telescope.  Charles Messier added it to his catalogue of faint deep sky objects in 1769, but the cluster is relatively bright and many believe that he only did this to boost the number in his catalogue in competition with his rival, the French astronomer Nicolas-Louis Lacaille.


The cluster has a magnitude of around 3.7 so is best viewed with binoculars or a small telescope.  The cluster is estimated to be around 600 million years old and approximately 600 light years away from us.  That means the light you will be observing left the stars 600 years ago and you are seeing the cluster how it was back in the 1400s when Henry V was on the throne! 



Monday 18th to Sunday 24th October 2021

The main event this coming week is the peak of the Orionids meteor shower on Thursday 21st.  Unfortunately we will be just past a Full Moon and this will spoil your view of the meteors as a Full Moon is the ultimate source of light pollution!  Astronomers looking for dim deep-sky objects will always avoid evenings around this time.  It's a shame because the Orionids is one of the best annual meteor showers.


The Orionids is so named because the meteors appear to originate from a single point in the constellation of Orion - this is known as the "radiant point".  You'll need to be looking east south east towards Orion after midnight and the meteors should be visible right through until dawn on the Thursday morning.  


The meteors or "shooting stars" are caused by the Earth "scooping up" debris left by a comet as it travelled close to the Sun on its orbit in from the outer reaches of the Solar System.  In the case of the Orionids, the debris comes from comet Halley that swings by the Earth every 75 years.


The dust and pea-sized debris it leaves behind enters the Earth's atmosphere at a speed of around 40 miles per second.  The streaks of light are produced by friction as the debris hits our air.

The best way to view the shower is to sit in a comfy chair facing Orion and wrap-up warm because you are not going to be moving around much.  Then just wait!  There is no need for a telescope or binoculars.



Monday 11th to Sunday 17th October 2021

Last week we talked about the phases of the Moon and I mentioned trying to see a dimly-lit Crescent Moon.  Now, further into the Moon's 29-day cycle, there is the chance to see a 67%-lit waxing Gibbous Moon on Thursday 14th October.


If you look to the south around 8pm local time, the Moon forms a triangle with Jupiter and Saturn.  The pair of gas giant planets is well-placed at the moment for observations with a telescope.


When observing the Moon, there are a series of visual effects known as "clair-obscur" originating from the French words meaning "light" and "shadow".  The interplay between sunlight falling on the lunar surface and your viewing angle creates easily-recognisable shapes.


If you aim your telescope towards the giant crater Clavius on Thursday 14th from about 7.30pm, you can see an effect known as the "Eyes of Clavius".  It looks like a pair of eyes staring out of the crater!


The diagram below of the different clair-obscur effects makes it easy to find Clavius, but please remember that if you are using an astronomical telescope rather than standard binoculars, everything will be upside down and back to front because there is no extra lens correcting the image!

Image and diagram courtesy of Sky at Night Magazine



Monday 4th to Sunday 10th October 2021

We'll start off with a visual challenge for the early risers on Tuesday 5th - the chance to see a 1% lit waning Crescent Moon appearing above the horizon to the east about an hour and a half before the Sun.  It is the optimal position to observe this if you can bear being up at 6am local time.


If an early start isn't to your liking, on the Thursday evening you could try spotting a 2% lit waxing Crescent Moon close to the south west horizon shortly after the Sun sets.

I'm often asked what the terms "waxing" and "waning" mean..........

Our Moon passes through different visible phases over a period of 29 days because it travels around us while we travel around the Sun, so all the angles keep changing.  The sunlight illuminating the side of the Moon facing us varies between 0% when we have a New Moon and 100% which is a Full Moon.


A waxing moon gets more sunlight on it as the days go by or in other words it's the period after a New Moon.  A waning moon progressively receives less sunlight - the days after a Full Moon.


There is an easy way to work out if the Moon is waxing or waning - if the illumination is to the right hand side, it is waxing and if to the left, waning.  This is only true in the Northern Hemisphere and assumes you are looking at the Moon with the naked eye or binoculars - astronomical telescopes always reverse the image!

Moon Phase diagram courtesy of NASA