October Astro Highlights (1)



Let’s look to see what Irregulars can observe with naked eyes, binoculars or a small telescope from London in October.


We’ll start with the Moon. In October there are two full moons; on the first  and  last day of the month.  It’s never a good idea to look at the Moon or the night sky during full moon as the glare of the Moon makes for any targets difficult to see, so it’s best not to observe a few before and after Full Moon.


The best time to observe features on the moon is at first quarter when the line dividing light and dark, called the terminator, is vertical and straight. The mountains and craters near the terminator appear in the best relief. Some of you were present  at the last Irregulars’ meeting at the Hub, on 2nd March, MoOnday, when we looked at the craters, mountains and ‘seas’ on the Moon at first quarter. In October first quarter falls on Friday October 23rd.


Turning to the planets, the gas giants Jupiter and Saturn remain visible low in the south. In the week beginning the 5th, Jupiter is due South just after 7pm preceding Saturn to the left. Both easily seen with the naked eye (Jupiter’s brightness is magnitude -2.21 and Saturn is dimmer at 0.56 – see here https://www.spaceacademy.net.au/library/notes/magntude.htm if you are unfamiliar with the ‘brightness’ scale used by astronomers). With binoculars, a steady support (an up-ended broom worked well for me!) and a clear atmosphere you will see some or all of the four largest moons of Jupiter (the Galilean moons) and the rings of Saturn. With a small telescope details of the planets’ atmospheres may be seen, particularly the two dark equatorial belts of Jupiter. Occasionally the famous Great Red Spot will be visible when Jupiter rotates about every ten hours. Observing with my 3” refractor from the Baker Street area the GRS is clearly discernible looking like a tiny grey oval dot. Various apps provide information on the positions of the Gallelian moons and the GRS – on my smartphone I use JupiterMoons app.


The ice giants Uranus and Neptune are also in the south, appearing as tiny discs in small telescopes. Both are invisible to the naked eye. Neptune at magnitude 7.8 is due south around 11pm BST mid month, followed by brighter Uranus (mag. 5.7) due south three hours later. The best time to see the pair is around New Moon which falls on Friday 16th. Between the two planets is Mars.


The Red Planet, Mars, still dominant in the south has been delighting urban-based astronomers for the past weeks. It is super bright, in mid month it will be at its brightest and largest this year, as seen from Earth, (mag – 2.6!) and apparent size of 22 arcseconds as it reaches opposition on night of Oct 13/14. See here https://in-the-sky.org/news.php?id=20201013_12_100&town=2643743 for what is a planetary opposition and here https://www.timeanddate.com/astronomy/planets/distance for apparent size or diameter (plug in Oct 13 at 01:00 in the Size in the Sky tab). 

I’ve been observing Mars recently, the bright white southern polar region and the contrast between darker and lighter features on the red surface were glimpsed during periods of good seeing using my small telescope. Many Irregulars have posted lovely images on our social media pages.


A planet appearing close to the Moon (a conjunction) is always a lovely sight to behold and a great photo opportunity. In October there are several conjunctions:


At 1:30am BST on Saturday the 3rd Mars is a little to the left and above the bright 99% illuminated Moon. By 4am the red planet is directly above our natural satellite. Mars is again close to the Moon later in the month on the 29th at 7:30pm GMT (Clocks go back at 2am on Sunday 25th), the Moon again bright and almost full (97% illuminated).

 For those with a clear view of the eastern horizon the 26 day old waning crescent Moon, 10% illuminated, is close to bright Venus in the pre-dawn hours of Wednesday 14th. 

And the gas giant Jupiter gets up close and personal to the Moon on Thursday 22nd very low in the south at 6:30 BST accompanied by Saturn to the left. If you have a clear view this trio should be a fine sight!

Deep Sky Objects


The Andromeda galaxy has been observed with small telescopes many times during our past meetings at the Hub (remember those?). Our satellite galaxy is well placed at New Moon at midnight on the 16th/17th. Try to observe this large but faint galaxy this month.


Other fine sights to observe are the Hercules globular cluster, the Pleiades open cluster, the Ring Nebula, the Double Cluster and the Owl Cluster. We will consider these in the next note.


We wish all Irregulars clear skies and safe observing.


Eric, for the Unofficial Force.


2020 September.