The night sky for October 2020

Northern Hemisphere

Ian Morison tells us what we can see in the Northern Hemisphere night sky during October 2020.

The Planets

• Jupiter Jupiter is now visible, low in the sky, just west of south when darkness falls as October begins and sets around 10:30 pm BST. Towards the end of the month it will be seen towards the southwest after sunset and sets by ~08:30 pm GMT. Its magnitude dims slightly from -2.4 to -2.2 during the month whilst its angular diameter falls from 40.5 to 37.1 arc seconds. Sadly, even when first seen after sunset, it will only have an elevation of ~14 degrees above the horizon so the atmosphere will limit our views. Due its position in the most southerly part of the ecliptic this has been a very poor opposition for those of us in the northern hemisphere..
  
  
• Saturn Saturn, following Jupiter into the sky, some 8 degrees behind at the start of the month but reducing to 5.2 degrees by Halloween, Saturn is best seen in the south just after sunset on the 1st. Its magnitude drops slightly during the month from +0.5 to +0.6 whilst its angular size decreases from 17.2 to 16.4 arc seconds. The rings span some 35 arc seconds across and, at ~22 degrees to the line of sight, show up well. Saturn lies in Sagittarius near the border of Capricornus. Saturn halted its retrograde motion on the 29th of September and, as the year progresses becomes closer to Jupiter until, on the 21st December they are just 0.1 degrees apart. Sadly again, its low elevation of ~16 degrees when crossing the meridian will somewhat limit our views of this most beautiful planet..
  
  
• Mercury Mercury passes in front of the Sun on the 25th of the month (inferior conjunction) and will not be visible this month..
  
  
• Mars See highlight above..
  
  
• Venus Venus, was at greatest elongation east back on August 12th but still dominates the pre-dawn sky rising around three hours before sunrise as October begins and a little less by month's end. It shines at magnitude -4.1 as October begins, lying some half a degree from Regulus in Leo, dropping to -4 by month's end whilst its angular size shrinks from 15.5 to 13.2 arc seconds. During the same time its its phase (the illuminated percentage of the disk) increases from 72% to 81% which is why the fall in magnitude is so small. It still reaches an elevation of ~32 degrees at sunrise. Venus entered the constellation of Leo on the 23rd of September and moves into Virgo on the 23rd of the month..
  
  

Highlights of the Month

• October - a great month to view Mars. During this opposition, Mar's southern hemisphere is tipped towards the Earth and so the South Polar Cap should be visible, though much of its frozen carbon dioxide will have vaporised during the Martian summer. Though the North Polar Cap is beyond our view, one should be able to spot the haze of the North Polar Hood lying above the northern limb of the planet. At 24.6 hours long, the Martian day is similar to ours, so the surface details remain similar at the same time each night. Mars takes 41 days to make an apparent rotation as seen from Earth..
  
  
• October - Find NeptuneThis month Neptune is just pass opposition and so will be visible during much of the night. It lies in Aquarius below one of the circlets in Pisces and shines at magnitude +7.8 having a 2.4 arc second disc so binoculars or a telescope will be needed to spot it under a dark sky. I hope the charts will help you find it - not so difficult as it lies close to a nice grouping of stars. Of course, a well aligned computerised telescope will take you right there but, unless the seeing is exceptional, I suspect that the dark bluish disk will not be that obvious..
  
  
• October, evening: the Double Cluster and the 'Demon Star', Algol. This month is a good time to look high in the east towards the constellations of Cassiopea and Perseus. Perseus contains two interesting objects; the Double Cluster between the two constellations and Algol the 'Demon Star'. Algol in an eclipsing binary system as seen in the diagram below. Normally the pair has a steady magnitude of 2.2 but every 2.86 days this briefly drops to magnitude 3.4..
  
  
• October: find M31 - The Andromeda Galaxy - and perhaps M33 in Triangulum Around new Moon (16th October) - and away from towns and cities - you may also be able to spot M33, the third largest galaxy after M31 and our own galaxy in our Local Group of galaxies. It is a face on spiral and its surface brightness is pretty low so a dark, transparent sky will be needed to spot it using binoculars (8x40 or, preferably, 10x50). Follow the two stars back from M31 and continue in the same direction sweeping slowly as you go. It looks like a piece of tissue paper stuck on the sky just a bit brighter than the sky background. Good Hunting!.
  
  
• October 2nd - 1 hour before sunrise - Venus and Regulus Before dawn on the 2nd of the month, if clear, one will spot Venus sining at magnitude -4.1 just half a degree to the upper right of Regulus, Alpha Leonis..
  
  
• October 10th - before dawn: The third quarter Moon close to Pollux in Gemini. Before dawn on the 10th of October, the third quarter Moon will lie down to the right of Pollux in Gemini..
  
  
• October 14th - before dawn : Venus and a very thin crescent Moon. Before dawn on the 14th should it be clear, Venus will be seen below a very thin waning crescent Moon. One may well be able to spot 'Earthshine' the dark side of the Moon lit by light reflected form the Earth..
  
  
• October 22nd - after sunset : Jupiter, Saturn and a waxing Moon After sunset on the 22nd, Jupiter will be seen above a waxing Moon, one day before first quarter with Saturn up to its left..
  
  
• October 29th - evening : Mars and a near full Moon.During the evening of the 29th, Mars will lies above the waxing Moon just 2 days before full..
  
  
• October 7th and 23rd evening: the Hyginus Rille For some time a debate raged as to whether the craters on the Moon were caused by impacts or volcanic activity. We now know that virtually all were caused by impact, but it is thought that the Hyginus crater that lies at the centre of the Hyginus Rille may well be volcanic in origin. It is an 11 km wide rimless pit - in contrast to impact craters which have raised rims - and its close association with the rille of the same name associates it with internal lunar events. It can quite easily be seen to be surrounded by dark material. It is thought that an explosive release of dust and gas created a vacant space below so that the overlying surface collapsed into it so forming the crater. On the evenings given above, the rille lies near the terminator..
  
  

Haritina Mogosanu and Samuel Leske from the Carter Science Centre in New Zealand speaks about the Southern Hemisphere night sky during October 2020.

SEE WITH THE NAKED EYE 

• Visible planets this month in order of disappearance:  Mercury, Jupiter, Saturn, and Mars. If you are lucky to have a flat horizon in the northeast and like planet Venus, you will be seeing it in the morning sky. This month, Mercury will reach its highest point in the evening sky on the 2nd of October and Mars will be at opposition, closest to Earth, on the 14th of October. Thus we will be able to easily see features from Mars in a telescope. 
  
  
• The Sun is in the zodiacal constellation of Virgo. It sets around 07:23PM and rises around 07:00AM.
  
  
• Mercury is in Virgo, about 9 light minutes away.
  
  
• Venus is in Leo, visually very close to the Sun. Is about 8 light minutes away. 
  
  
• Mars is visually in the zodiacal constellation Pisces, at a distance of just about 4 light minutes away. 
  
  
• Jupiter is in the constellation of Sagittarius of about 40 light minutes from Earth.
  
  
• Saturn is visually in Sagittarius, 80 light minutes away. 
  
  

SEE WITH BINOCULARS AND TELESCOPE

• Uranus is in Aries. It has a visual magnitude of +5.7 so under a very dark sky and if you have amazingly good eyes you might be able to see it, with the naked eye. It’s about 158 light minutes away approx. 
  
  
• Neptune is in the evening sky, in Aquarius. It takes light approximately 4 hours to reach us from Neptune. At a visual magnitude of +7.8 you will need binoculars or telescopes to see it. 
  
  
• Pluto in Sagittarius, very close to Jupiter. We cannot see Pluto with the naked eye, as it has a magnitude of +14.4 is 5059 million kilometres away, at about 281 light minutes – more than 4 hours and 30 light minutes. 
  
  

IN OCTOBER

• The Milky Way’s centre is now on the western horizon after sunset. Scorpius and Sagittarius are the two constellations whose stars are between us and the galactic centre. We are very lucky here in New Zealand to see the centre of the Milky Way high in the sky, which means we are looking at it through less layers of atmosphere than in the Northern Hemisphere. In the Northern Hemisphere, from mid latitudes, the centre of the Milky Way climbs only about 30 degrees above the horizon. 
  
  
• October is a good month to still see many deep sky objects. The majority of them are around the galactic bulge. In Scorpius, our favourites are: Ptolemy’s cluster – M7 a beautiful open cluster of stars, the Butterfly Cluster – M6, which resembles a butterfly, and the globular clusters Messier 4 and Messier 80. The Bug Nebula NGC 6302 and The Cat’s Paw nebula – NGC 6334 are excellent astrophotography targets. Neighbouring Scorpius is Sagittarius. This is the constellation where we map the centre of our galaxy, the Milky Way. Sagittarius’s famous asterism (grouping of stars) is the teapot, which is visible upside down here in New Zealand. Sagittarius cannot be seen from Scotland or Scandinavia. We are very lucky here to be able to observe it overhead.
  
  
• The Milky Way is at its densest in Sagittarius.  Inside the constellation, which is a patch of the sky, we can admire two beautiful Star Clouds, easily seen in binoculars: the Large Sagittarius Star Cloud and the Small Sagittarius Star Cloud – Messier 24. Some stunning deep sky objects in Sagittarius are Lagoon Nebula – M8, Omega Nebula or Swan Nebula and the Trifid Nebula, another famous one also known as M20. The Trifid Nebula is about 2 degrees from Lagoon Nebula.
  
  
• In the circumpolar region, the Small Magellanic Cloud is in a good position to observe. Close to it, 47 Tucanae is one of the most beautiful and large globular clusters that adorn the night sky. 47 Tucanae is the second brightest globular cluster in the sky and one of the most massive clusters in the Galaxy. It’s angular diameter is roughly the size of the full Moon, that is the width of your pinky at arm’s length. It can be seen with the naked eye from Earth although it is far far away, about 13,000 light years from Earth.
  
  
 The three famous crosses of the southern sky, the Southern Cross, Diamond Cross and the false cross are very low on the horizon, and for the next three months we will be looking at them through an extra layer of atmosphere. 

Some notable deep sky objects this month are Helix Nebula in Aquarius, Dumbbell Nebula in Vulpecula and the Grus Quartet in Grus. Famous for its nickname “The Eye of Sauron” Helix Nebula is a very large planetary nebula. Dumbbell Nebula – M27 in Vulpecula is very bright and the first planetary nebula to be discovered. In Grus, a gathering of four interacting galaxies are known as the Grus Quartet. They are fascinating to see in a large telescope. 



Bright Objects

Beautiful bright stars are visible in the night sky. Right at the top of the sky, Antares, the red giant and main star from Scorpius shimmers in an incredibly beautiful red colour as seen through a telescope. On the southern horizon lays Canopus, glistening all colours, including red and green as we see it through the atmosphere. On the opposite side, on the northern horizon is Altair, the main star in Aquila.

Just after sunset, at the beginning of the month, you can catch a good view of planet Mercury, which now reaches its highest point in the sky and sets about two hours after the Sun. Jupiter and Saturn are evening objects, they are visible at Zenith. Mars is visible after 9 PM and Venus is just slightly visible in the morning, rising one hour before the Sun.