Night sky guide for October 2016

October will bring us the first of three supermoons for 2016. On October 16, the full moon will take place unusually close to the time of the month when the Moon also makes its closest approach to the Earth – called its perigee. This near coincidence between a full moon and lunar perigee will mean that this full moon will appear slightly larger and brighter than usual in the night sky – supermoon.

We'll see two meteor showers this month.

Draconid meteor shower, unusual in that the best viewing time is in the early evening instead of early morning like most other showers, will peak on October 7 with about 10 meteors per hours. The first quarter moon will block the fainter meteors in the early evening.

Orionid meteor shower will reach its peak on the nights of October 20 and 21 with up to 20 meteors per hour. The Moon will be 20 days old at the time of peak activity, and so will present significant interference in the pre-dawn sky. 

The best time of the month to observe faint objects such as galaxies and star clusters – new moon – is on October 1 and 30.

• October 1 – New moon – 00:12 UTC. The Moon will be located on the same side of the Earth as the Sun and will not be visible in the night sky. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

• October 7 – Draconid meteor shower. This is a minor meteor shower producing only about 10 meteors per hour. It is produced by dust grains left behind by comet 21P Giacobini-Zinner, which was first discovered in 1900. It is an unusual shower in that the best viewing is in the early evening instead of early morning like most other showers. The first quarter moon will block the fainter meteors in the early evening. It will set shortly after midnight leaving darker skies for observing any lingering stragglers. Best viewing will be in the early evening from a dark location far away from city lights. Meteors will radiate from the constellation Draco, but can appear anywhere in the sky. Draconids run annually from October 6 – 10.

• October 14 – M33 well placed for observation. The Triangulum galaxy (M33) will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +30°39', it is easiest to see from the northern hemisphere and cannot be seen from latitudes much south of 39°S. At magnitude 5.7, M33 is too faint to be seen with the naked eye from any but the very darkest sites, but is visible through a pair of binoculars or a small telescope.

• October 15 – Conjunction between the Moon and Uranus – 02:54 UTC. The Moon and Uranus will make a close approach, passing within 2°42' of each other. At the moment of closest approach, the Moon will be at mag -12.8, and Uranus at mag 5.7, both in the constellation Pisces. The pair will be too widely separated to fit within the field of view of a telescope, but will be visible to the naked eye or through a pair of binoculars.

• October 15 – Uranus at opposition – 10:30 UTC. Uranus will be at its closest approach to Earth and its face will be fully illuminated by the Sun. It will be brighter than any other time of the year and will be visible all night long, making this is the best time to view Uranus. Due to its distance, the planet will only appear as a tiny blue-green dot in all but the most powerful telescopes. Over the weeks following its opposition, Uranus will reach its highest point in the sky four minutes earlier each night, gradually receding from the pre-dawn morning sky while remaining visible in the evening sky for a few months.

• October 16 – Full moon / supermoon – 04:24 UTC. This month's full moon will take place unusually close to the time of the month when the Moon also makes its closest approach to the Earth – called its perigee. This near coincidence between a full moon and lunar perigee will mean that this full moon will appear slightly larger and brighter than usual in the night sky – supermoon, the first of three supermoons for 2016. Full moons such as this occur roughly once every 13 months. This full moon was known by early Native American tribes as the Full Hunters Moon because at this time of year the leaves are falling and the game is fat and ready to hunt. This moon has also been known as the Travel Moon and the Blood Moon.

• October 20 – Ceres at opposition. Ceres will be well placed for observation, in the constellation Cetus. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time. Over the weeks following its opposition, Ceres will reach its highest point in the sky four minutes earlier each night, gradually receding from the pre-dawn morning sky while remaining visible in the evening sky for a few months.

• October 20, 21 – Orionid meteor shower. This is an average shower producing up to 20 meteors per hour at its peak. It is produced by dust grains left behind by comet Halley, which has been known and observed since ancient times. The shower runs annually from October 2 to November 7 and it peaks this year on the night of October 21 and the morning of October 22. The Moon will be 20 days old at the time of peak activity, and so will present significant interference in the pre-dawn sky. However, Orionids tend to be fairly bright so it could still be a good show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Orion, but can appear anywhere in the sky.

• October 22 – Asteroid 18 Melpomene at opposition – 20:28 UTC. Asteroid 18 Melpomene will be well placed for observation, lying in the constellation Cetus, well above the horizon for much of the night. Regardless of your location on the Earth, 18 Melpomene will reach its highest point in the sky at around midnight local time.

• October 25 – NGC 869 well placed for observation. The open star cluster NGC 869 in Perseus, also known as the western half of the double cluster will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +57°09', it is easiest to see from the northern hemisphere and cannot be seen from latitudes much south of 12°S. At magnitude 4.0, NGC869 is tricky to make out with the naked eye except from a dark site, but is visible through a pair of binoculars or a small telescope.

• October 26 – NGC 884 well placed for observation. The open star cluster NGC 884 in Perseus, also known as the eastern half of the double cluster will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +57°07', it is easiest to see from the northern hemisphere and cannot be seen from latitudes much south of 12°S. At magnitude 4.0, NGC884 is tricky to make out with the naked eye except from a dark site, but is visible through a pair of binoculars or a small telescope.

• October 27 – Mercury at superior solar conjunction. Mercury will pass very close to the Sun in the sky as its orbit carries it around the far side of the Solar System from the Earth. This occurs once in every synodic cycle of the planet (116 days), and marks the end of Mercury's apparition in the morning sky and its transition to become an evening object over the next few weeks. At closest approach, Mercury and the Sun will appear at a separation of only 0°30', making Mercury totally unobservable for several weeks while it is lost in the Sun's glare. Mercury will also pass apogee – the time when it is most distant from the Earth – at around the same time, since it will lie exactly opposite to the Earth in the Solar System. It will move to a distance of 1.43 AU from the Earth, making it appear small and very distant. If it could be observed, it would measure 4.7 arcsec in diameter, whilst appearing completely illuminated.

• October 29 – Mars at perihelion. Mars's 687-day orbit around the Sun will carry it to its closest point to the Sun – its perihelion – at a distance of 1.38 AU. Unlike most of the planets, which follow almost exactly circular orbits around the Sun which only vary in their distance from the Sun by a few percent, Mars has a significantly elliptical orbit. Its distance from the Sun varies between 1.38 AU and 1.67 AU – a variation of over 20% – meaning that it receives 31% less energy from the Sun at aphelion as compared to perihelion.

• October 29 – Conjunction between Venus and Saturn. Venus and Saturn will make a close approach, passing within 2°59' of each other. At the moment of closest approach, Venus will be at mag -4.4, and Saturn at mag 0.3, both in the constellation Ophiuchus. The pair will be too widely separated to fit within the field of view of a telescope, but will be visible to the naked eye or through a pair of binoculars.

• October 30 – New moon – 17:40 UTC. At new moon, the Earth, Moon and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare. In this configuration, we see almost exactly the opposite half of the Moon to that which is illuminated by the Sun, making it doubly unobservable because the side we see is almost entirely unilluminated. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

• October 31 – Fornax well placed for observation. Across much of the world, the Fornax dwarf spheroidal galaxy will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -34°27', it is easiest to see from the southern hemisphere and cannot be seen from latitudes much north of 35°N. At magnitude 9.0, Fornax is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• October 31 – Venus at aphelion – 08:25 UTC. Venus's 225-day orbit around the Sun will carry it to its furthest point to the Sun – its aphelion – at a distance of 0.73 AU. However, Venus's orbit is very close to circular. Its distance from the Sun varies by only about 1.5% between perihelion and aphelion. This makes Venus's orbit more perfectly circular than that of any of the Solar System's other planets. As a result, its surface receives almost exactly the same amount of energy from the Sun at perihelion (closest approach to the Sun) and aphelion (furthest recess from the Sun).

• October 31 – Moon at apogee – 19:29 UTC. The Moon will reach the furthest point along its orbit to the Earth, and as a result will appear slightly smaller than at other times. The Moon's distance from the Earth varies because its orbit is not perfectly circular – it is instead slightly oval-shaped, tracing out a path called an ellipse.

Video courtesy Hubble Space Telescope

Sources: InTheSky (Dominic Ford), SeaSky

Featured image background: Draconids by Jeremy Evans