Night sky guide for December 2017

Night sky guide for December 2017

The year ends with the first and last supermoon of the year, the first of 3 over the next 60 days, one royal meteor shower, and December solstice. Hopefully, this year made us all stronger, wiser and ready for what's to come in 2018 and beyond.

  • December 1 - Asteroid 349 Dembowska at opposition - 08:21 UTC. Asteroid 349 Dembowska will be well placed for observation, lying in the constellation Taurus, well above the horizon for much of the night. Regardless of your location on the Earth, 349 Dembowska will reach its highest point in the sky at around midnight local time.

  • December 3 - Full Moon, Supermoon - 15:48 UTC. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This is the first and only supermoon in 2017. It will take place unusually close to the time of a month when the Moon also makes its closest approach to Earth - called its perigee. This means it will appear slightly larger and brighter than other times, though any difference is imperceptible to the naked eye. Perigee full moons such as this occur roughly once every 13 months.This full moon was known by early Native American tribes as the Full Cold Moon because this is the time of year when the cold winter air settles in and the nights become long and dark. This moon has also been known as the Full Long Nights Moon and the Moon Before Yule.

Video courtesy NASA

  • December 6 - Conjunction of Saturn and Mercury - 11:07 UTC. Saturn and Mercury will share the same right ascension, with Saturn passing 1°21' to the north of Mercury. Saturn will be at mag 0.4, and Mercury at mag 1.3, both in the constellation Sagittarius. 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.

  • December 7 - Puppid-Velid meteor shower. This is a minor meteor shower (Class II), running annually from December 1 - 17. Its peak activity this year is expected on December 7 with up to 18 meteors per hour. The moon will be 19 days old, presenting significant interference in the pre-dawn sky.

  • December 9 - C/2015 F5 (SWAN-Xingming) at perihelion. Comet C/2015 F5 (SWAN-Xingming) will make its closest approach to the Sun, at a distance of 0.78 AU.

  • December 9 - C/2015 F5 (SWAN-Xingming) reaches its brightest. Comet C/2015 F5 (SWAN-Xingming) will reach its brightest, at around magnitude 10.4. It will lie at a distance of 0.78 AU from the Sun, and at a distance of 1.03 AU from the Earth.

  • December 10 - Moon at Last Quarter - 08:53 UTC. The Moon will be prominent in the dawn sky, rising at around midnight. Over the coming days, it will rise later each day, so it is visible for less time before sunrise. Perfect for the upcoming Geminid meteor shower.

  • December 12 - LMC well placed for observation. Across much of the world the Milky Way's dwarf companion, the Large Magellanic Cloud (LMC), in Dorado will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -69°45', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 0°N. At magnitude 0.9, LMC is visible to the naked eye, but best viewed through a pair of binoculars.

  • December 13 - Mercury at inferior solar conjunction - 01:43 UTC. Mercury will pass very close to the Sun in the sky as its orbit carries it between the Sun and Earth. This occurs once in every synodic cycle of the planet (116 days) and marks the end of Mercury's apparition in the evening sky and its transition to become a morning object over the next few weeks. At closest approach, Mercury will appear at a separation of only 1°43' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare. Mercury will also pass perigee – the time when it is closest to the Earth – at around the same time since it will lie on exactly the same side of the Sun as the Earth in the Solar System. It will move to within a distance of 0.68 AU from the Earth, making it appear with its largest angular size. If it could be observed, it would measure 9.9 arcsec in diameter, whilst appearing completely unilluminated.

  • December 13 - Conjunction of the Moon and Mars - 16:29 UTC. The Moon and Mars will share the same right ascension, with the Moon passing 4°09' to the north of Mars. The Moon will be 25 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -10.8, and Mars at mag 1.6, both in the constellation Virgo. 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.

  • December 13 - Close approach of the Moon and Mars - 19:14 UTC. The Moon and Mars will make a close approach, passing within 3°56' of each other. The Moon will be at mag -10.7, and Mars at mag 1.6, both in the constellation Virgo. 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.

  • December 13, 14 - Geminids Meteor Shower. This is a major, Class I meteor shower - the king of meteor showers. Considered by many as the best meteor shower and producing up to 120 multicolored meteors per hour, Geminids are leftovers of an asteroid known as 3200 Phaethon, discovered in 1982. It runs annually from December 7 - 17, and peaks this year on the night of December 13 and the morning of the 14th. The Moon will be 26 days old at the time of peak activity, presenting minimal interference. To see the most meteors, the best place to look is not directly at the radiant itself, but at any dark patch of sky which is around 30–40° away from it. It is at a distance of around this distance from the radiant that meteors will show reasonably long trails without being too spread out.

  • December 14 - NGC 1981 well placed for observation. The open star cluster NGC 1981 in Orion's sword will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -04°25', it is visible across much of the world; it can be seen at latitudes between 65°N and 74°S. At magnitude 4.6, NGC1981 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.

  • December 14 - Conjunction of the Moon and Jupiter - 14:27 UTC. The Moon and Jupiter will share the same right ascension, with the Moon passing 4°14' to the north of Jupiter. The Moon will be 26 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -10.3, and Jupiter at mag -1.8, both in the constellation Libra. 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.

  • December 14 - Close approach of the Moon and Jupiter - 16:58 UTC. The Moon and Jupiter will make a close approach, passing within 4°03' of each other. The Moon will be at mag -10.2, and Jupiter at mag -1.8, both in the constellation Libra. 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.

  • December 17 - Asteroid 20 Massalia at opposition - 17:45 UTC. Asteroid 20 Massalia will be well placed for observation, lying in the constellation Taurus, well above the horizon for much of the night. Regardless of your location on the Earth, 20 Massalia will reach its highest point in the sky at around midnight local time.

  • December 18 - New Moon - 06:32 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.

  • December 21 - December Solstice - 16:16 UTC. December 21 will be the shortest day of 2017 in the northern hemisphere, midwinter day. This is the day of the year when the Sun's annual path through the constellations of the zodiac reaches its most southerly point in the sky, in the constellation of Capricornus at a declination of 23.5°S. On this day, the Sun is above the horizon for the less time than on any other day of the year in the northern hemisphere. This is counted by astronomers to be the first day of winter. Conversely, in the southern hemisphere, the Sun is above the horizon for longer than on any other day of the year, and astronomers define this day to be the first day of summer. At the solstice, the Sun appears overhead at noon when observed from locations on the tropic of Capricorn, at a latitude 23.5°S.

  • December 21 - Saturn at solar conjunction - 21:12 UTC. Saturn 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. At closest approach, Saturn will appear at a separation of only 0°54' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare. At around the same time, Saturn will also be at its most distant from the Earth – receding to a distance of 11.05 AU – since the two planets will lie on opposite sides of the solar system. If Saturn could be observed at this time, it would appear at its smallest and faintest on account of its large distance. It would measure 15.0 arcsec in diameter. Over following weeks and months, Saturn will re-emerge to the west of the Sun, gradually becoming visible for ever-longer periods in the pre-dawn sky. After around six months, it will reach opposition, when it will be visible for virtually the whole night.

  • December 21, 22 - Ursid Meteor Shower. This is another major meteor shower - Class I -  but it's producing between 5 and 10 meteors per hour. It is produced by dust grains left behind by comet Tuttle, which was first discovered in 1790. The shower runs annually from December 17 - 24 and this year It peaks this year on the night of the 21st and morning of the 22nd. The crescent moon will set early in the evening leaving dark skies for optimal observing. Best viewing will be just after midnight from a dark location far away from city lights. Meteors will radiate from the constellation Ursa Minor, but can appear anywhere in the sky.

  • December 26 - Moon at First Quarter - 09:22 UTC. The Moon will be prominent in the evening sky, setting around midnight. At this time in its monthly cycle of phases, it appears almost exactly half illuminated. Over coming days, the Moon will set later each day, becoming visible for more of the night. Within a few days, it will not make it very far above the eastern horizon before nightfall. By the time it reaches full phase, it will be visible for much of the night, rising at around dusk and setting at around dawn.

  • December 27 - NGC 2232 well placed for observations. The open star cluster NGC 2232 in Monoceros will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -04°45', it is visible across much of the world; it can be seen at latitudes between 65°N and 74°S. At magnitude 3.9, NGC2232 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.

  • December 28 - Mercury at dichotomy - 23:23 UTC. Mercury will be well placed for observation in the dawn sky, shining brightly at mag -0.2. Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few days each time it reaches greatest separation from the Sun – moments referred to as greatest elongation.

  • December 29 - NGC 2244 well placed for observation. The open star cluster NGC 2244, in the rosette nebula in Monoceros will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +04°52', it is visible across much of the world; it can be seen at latitudes between 74°N and 65°S. At magnitude 4.8, NGC2244 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.

Video courtesy Hubble Space Telescope

Sources: American Meteor SocietyIn The Sky by Dominic Ford

Featured image credit: Bhador

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