Our monthly astronomy guide for stargazers
◼ Bright Mars is at opposition and visible all night long. Jupiter and Saturn are in the evening sky and can be seen as soon as darkness falls. Venus is shining brilliantly before dawn. Look for variable star Mira, shining at its brightest. Conditions are ideal for the Orionid meteor shower. There are two full moons in October – on the 1st and the 31st. Here’s more about the stars and planets you can see in the night sky in October 2020.
October’s star chart
Click on the image above, or the following text for an interactive map of constellations visible in the sky. It can be adjusted for any time and date.
We also have a map of the night sky set up for mid-latitudes in the southern hemisphere.
The stars in October 2020
For countries in the northern hemisphere, the nights continue to lengthen with more hours of darkness in which to enjoy the stars.
As it gets dark in early October, northern skywatchers can spot the Summer Triangle roughly due south in the heavens. This is not a constellation in itself, but a pattern made up of the brightest stars in three others – Vega in Lyra, Deneb in Cygnus, and Altair in Aquila. The Milky Way runs overhead, though Cygnus and down to the southern horizon. From northerly latitudes, the centre of the galaxy, with the richest part of the Milky Way, lies low over the southern horizon at this time, in Sagittarius.
Over to the east, the Great Square of Pegasus hangs above the horizon, though the star marking the upper left (north-eastern) corner of this square actually belongs to the neighbouring constellation of Andromeda. Look along the line of stars of Andromeda to see the extended glow of Messier 31, the Andromeda Galaxy, which is unmissable with binoculars.
Not far below Andromeda, as seen from northern latitudes, you can find a smaller galaxy, Triangulum, that is home to another nearby galaxy, Messier 33.
North of Andromeda lies Cassiopeia which looks like the letter “w” in the evening at this time of year. Between Andromeda and the bright star Capella in the north-east, you can find Perseus, a constellation with some fine sights including the Double Cluster and a famous eclipsing variable star, Algol.
Over in the western sky, constellations sinking towards the horizon during September evenings include Hercules, Bootes and Corona Borealis.
The planets in October 2020
Mercury reaches its greatest eastern elongation in the evening sky on 1 October, but whether or not you can see it depends on where you are in the world. From northern latitudes, the planet will be too low over the horizon to see as dusk fades. But if you are observing from equatorial latitudes, or in the southern hemisphere, Mercury will lie much higher in the sky in the twilit sky, and be easier to see for the first week or so, as long as you have a clear western horizon. As the month opens, Mercury will shine at zero magnitude, which is brighter than most stars. During the second week of October, it will be sinking back towards the Sun and fading too, becoming only half as bright, and tricky to observe by the 14th. Read more about Mercury.
Venus remains a dazzling object in the morning sky, rising four hours before the Sun at the start of October. It will then lie in Leo, close to its brightest star Regulus (α Leonis). Watch as it closes in on this first-magnitude star, until they lie just 12 arc minutes apart at 02:20 UT on 3 October. This is before the planet rises from the UK, western Europe and, indeed, the USA. However they will still present a close and interesting spectacle when they do lift above your local horizon. Venus, shining at magnitude -4, will be very much brighter than Regulus. Watch over the next few mornings as Venus rapidly moves away from Regulus. The waning crescent Moon will lie close to Venus on the 14th, offering a nice photographic opportunity. Read more about planet Venus, and also see our guide to observing Venus.
Mars reaches opposition on 13 October – when it will lie on the opposite side of the sky to the Sun – offering the best opportunity to see it well since July 2018. With Mars and Earth lying on the same side of the Sun, the Red Planet shines at a brilliant -2.6 magnitude in the constellation of Pisces. Mars now shows a diameter of more than 22 arc-seconds, more than five times its apparent size at the start of this year when it was much further away. Because of the non-circular shapes of our orbits, Mars actually gets closest to Earth a week before opposition, on 6 October, when it will lie just over 62 million km from us. Even a small telescope will show some detail on the martian rusty-coloured disk. A larger instrument will be able to pick out dark features, as well as the prominent white south polar cap, which is tilted towards us. Being at opposition, Mars will be visible throughout the night. The Full Moon will lie close by in the sky on the night of the 2nd/3rd, so don’t miss the chance to get a great photo! In fact, if you aim a telephoto lens at the Moon after sunrise, Mars will be bright enough to appear in the photo, despite the broad daylight. Read our guide to Mars.
Giant planet Jupiter is visible from nightfall and now sets before midnight at the start of October. It is another planet that is currently on a southerly part of the ecliptic, in the constellation of Sagittarius, the view is much better from southern latitudes, such as Australia, New Zealand, South Africa, or South America, where Jupiter will be high in the sky.
It is now shining brightly, though fading slightly from magnitude -2.2 to -2.1 over the course of the month, so is easy to spot, despite being low down for observers in the northern hemisphere.
Even a small telescope will reveal the cloud belts on Jupiter and its four main moons, the Galilean satellites Io, Europa, Ganymede and Callisto. The planet Saturn lies a little to the east of Jupiter. The Moon will be close by on the night of the 22nd. Read more about planet Jupiter.
The ringed planet, another gas giant, is also visible from dusk until soon after midnight as October opens. Saturn shines at around magnitude 0.6, like one of the brightest stars, and with a yellowish light. Sadly again for northern hemisphere observers, Saturn is low in the sky, lying not far from Jupiter, in the constellation of Sagittarius. The pair are gradually closing together and will be in very close conjunction in December. From the southern hemisphere, Saturn rises higher in the sky, and so this will be an ideal time to observe it and its beautiful rings. Read more about Saturn.
Uranus lies in the constellation of Aries, and is another planet to reach opposition in October, on the 31st. It will then be visible all night long. In a dark sky, this planet is theoretically visible with the unaided eye, shining at a dim magnitude 5.7. However, you are unlikely to see it without binoculars, while a telescope will help to reveal its greenish disk. Read more about Uranus.
The outer ice giant was at opposition in September and so is visible from nightfall for most of the night, in the constellation of Aquarius. It is a couple of magnitudes fainter than its twin, Uranus, and shines at magnitude 7.8 this month. You will be able to glimpse it with binoculars, or a small telescope. Read more about Neptune.
Meteors from Halley’s Comet
One of the year’s more reliable meteor showers, the Orionids, can be seen in October. These “shooting stars” are dust left by Halley’s Comet and one of two annual showers from that comet. The official limits of activity for the Orionids are from October 2 to November 7, with the peak occurring on the night of October 22-23. Rates seen for a single observer under ideal conditions are expected to be around a moderate 20 meteors per hour, so observing around the peak date will give you the best chance of seeing anything.
On the night of maximum, the shower’s radiant, in the club wielded by mighty hunter Orion, rises at around 10pm local time from mid-northern latitudes. You won’t see any Orionids before then when it is below the horizon. The Moon will be a waxing crescent, setting by late evening on the night of maximum, making this a great year to watch the Orionids.
Related: About the Orionid meteor shower
Update: Meteor experts are also advising that there could be enhanced activity from the Draconid meteor shower on the night of the 6/7 October, when Earth brushes two streams of dust.
Variable star Mira is at its best
One of the most interesting stars in the night sky for casual sky-watchers is Mira, or ο Ceti, because it has a huge range in brightness. Mira can brighten to second magnitude, making it easy to see with the unaided eye, but regularly fades to as faint as tenth magnitude when a small telescope is needed to see it! At the end of August, Mira had brightened to magnitude 4, making it a naked-eye sight in a dark sky. It is expected to be brightest in October. Why not check it out for yourself? Here is our special guide to observing Mira.
Full Moon: Oct 1
Last Quarter: Oct 10
New Moon: Oct 16
First Quarter: Oct 23
Full Moon: Oct 31
The Moon always makes a great target for a small telescope, which come into view as its phases change. We’ve a guide to where to find 50 of the best lunar features, plus a checklist to download so you can tick them off as you spot them! Don’t have a telescope? Here’s our guide to choosing one.
Fifty fantastic features – our amazing Moon
Here’s our guide to observing some of the finest sights on the Moon with small telescopes. Our pages of charts will help you find interesting features to seek out yourself, including craters, lava flows, mountain ranges and deep chasms!
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