Night sky guide for December 2016

Night sky guide for December 2016

The last of three supermoons for this year will occur on December 14. Over the nights following December 14, the Moon will rise around an hour later each day, becoming prominent later in the night. Within a few days, it will only be visible in the pre-dawn and early-morning sky.

December hosts 3 meteor showers - Geminids on 13th and 14th, Ursids on 21st and 22nd and Puppid-Velids on the 26th

The first day of winter (winter solstice) in the northern hemisphere and the first day of summer (summer solstice) in the southern hemisphere - December Solstice - will occur on the 21st.

The best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere - new moon - is on December 29.

  • December 10 - Conjunction of the Moon and Ceres - 01:46 UTC. The Moon and 1 Ceres will share the same right ascension, with the Moon passing 6°07' to the north of 1 Ceres. The Moon will be at mag -12.5 in the constellation Pisces, and 1 Ceres at mag 7.3 in the neighboring constellation of Cetus.

  • December 10 - Conjunction of the Moon and Eris - 06:10 UTC. The Moon and 136199 Eris will share the same right ascension, with the Moon passing 9°14' to the north of 136199 Eris. The Moon will be at mag -12.6 in the constellation Pisces, and 136199 Eris at mag 18.7 in the neighboring constellation of Cetus.

  • December 10 - Saturn at solar conjunction - 11:55 UTC. From our vantage point on the Earth, Saturn will appear very close to the Sun in the sky as it passes around the far side of the solar system from the Earth. At closest approach, Saturn and the Sun will appear at a separation of only 1°17', making Saturn 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 11.03 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 15.1 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. A chart of the path of Saturn across the sky in 2016 can be found here, and a chart of its rising and setting times here.

  • December 11 - 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 and 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 11 - Mercury at greatest elongation east - 07:45 UTC. In the southern hemisphere, Mercury will be well placed for observation in the evening sky, shining brightly at mag -2.3. 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. These apparitions take place alternately in the morning and evening skies, depending whether Mercury lies to the east of the Sun or to the west. When it lies to the east, it rises and sets a short time after the Sun and is visible in early evening twilight. When it lies to the west of the Sun, it rises and sets a short time before the Sun and is visible shortly before sunrise. On this occasion, it lies 20° to the Sun's east.

  • December 13, 14 - Geminid meteor shower. This is the king of the meteor showers. It is considered by many to be the best shower in the heavens, producing up to 120 multicolored meteors per hour at its peak. It is produced by debris left behind by an asteroid known as 3200 Phaethon, which was discovered in 1982. The shower runs annually from December 7 - 17. It peaks this year on the night of the 13th and morning of the 14th. The nearly full moon will block out many of the fainter meteors this year, but the Geminids are so bright and numerous that it could still be a good show. The maximum rate of meteors expected to be visible from a dark location is around 100 per hour (ZHR). 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 - Full Moon, Supermoon - 00:07 UTC. The Moon will reach full phase at 00:07 UTC on December 14. At this time in its monthly cycle of phases, the Moon lies almost directly opposite the Sun in the sky, placing it high above the horizon for much of the night. This month's full moon will take place unusually close to the time of 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. Full moons such as this occur roughly once every 13 months. The sequence of full moons through the year are often assigned names according to the seasons in which they fall. This month's will be the third to fall in autumn 2016 – the Oak Moon. Over the nights following December 14, the Moon will rise around an hour later each day, becoming prominent later in the night. Within a few days, it will only be visible in the pre-dawn and early-morning sky. By the time it reaches last quarter, a week after full moon, it will rise at around midnight and set at around noon. At the exact moment when the Moon reaches full phase, it will lie at a declination of +18°23' in the constellation Taurus, and so will appear highest in the northern hemisphere. It will be visible from all latitudes south of 61°S. Its distance from the Earth will be 359 000 km (223 072 miles). 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. This is also the last of three supermoons for 2016.

  • 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 - Mercury at dichotomy - 16:40 UTC. In the southern hemisphere, Mercury will be well placed for observation in the evening sky, shining brightly at mag -2.4. 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. Mercury's phase - Mercury's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon. Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times. Mercury shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few hours, only because Venus's orbit is not quite perfectly aligned with the ecliptic. Over coming weeks, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare. 

  • December 15 - Mercury at greatest brightness - 06:59 UTC. Mercury's brightness depends on two factors: its closeness to the Earth, and its phase. Its phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon. Mercury reaches its brightest when it is still a crescent – with less than half of its disk illuminated. This is because it is much closer to the Earth during its crescent phases than at other times. As a result, during evening apparitions, Mercury reaches maximum brightness a few days after it is at greatest separation from the Sun, which always coincides with it showing half-phase (dichotomy). Conversely, during morning apparitions, Mercury reaches maximum brightness a few days before it is at greatest separation from the Sun.

  • December 21 - December solstice - 10:37 UTC.  This is the first day of winter (winter solstice) in the northern hemisphere and the first day of summer (summer solstice) in the southern hemisphere. This is the day of the year when the Sun's annual passage through the constellations of the zodiac carries it to its most northerly 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, though meteorologists more usually consider winter to start on December 1. 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 December solstice, the Sun appears overhead at noon when observed from locations on the tropic of Capricorn, at a latitude 23.5°S. Midwinter is best known in the western world because Christmas borrows its date from ancient pagan midwinter festivals. In the modern calendar, however, Christmas falls a few days after astronomical midwinter. This happens because the system of leap days which are sometimes inserted into our calendar on February 29 was only refined to its present form by the Gregorian calendar reforms of the 16th century. Before this, the average length of each year did not quite match the period of time with which the seasons repeat – 365.2422 days – and so the seasons drifted through the year by a small amount each century.

  • December 21, 22 - Ursid meteor shower. This is a minor meteor shower producing about 5-10 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 17-25. It peaks this year on the the night of the 21st and morning of the 22nd. The second quarter moon will block many of the fainter meteors. But if you are patient, you might still be able to catch a few of the brighter ones. 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 22 - Conjunction of the Moon and Makemake - 09:17 UTC. The Moon and 136472 Makemake will share the same right ascension, with the Moon passing 27°26' to the south of 136472 Makemake. The Moon will be at mag -11.5 in the constellation Virgo, and 136472 Makemake at mag 16.9 in the neighboring constellation of Coma Berenices.

  • December 22 - Close approach of the Moon and Jupiter - 18:14 UTC. The Moon and Jupiter will make a close approach, passing within 2°17' of each other. The Moon will be at mag -11.4, and Jupiter at mag -1.9, 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 23 - Conjunction of the Moon and Haumea - 22:10 UTC. The Moon and 136108 Haumea will share the same right ascension, with the Moon passing 25°01' to the south of 136108 Haumea. The Moon will be at mag -11.0 in the constellation Virgo, and 136108 Haumea at mag 17.3 in the neighboring constellation of Bootes.

  • December 26 - Puppid-Velid meteor shower. Some shooting stars associated with the shower are visible each night from 17 November to January. The maximum rate of meteors expected to be visible from a dark location is around 15 per hour (ZHR). The Moon will be 27 days old at the time of peak activity, and so will present 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.

  • December 27 - NGC 2232 well placed for observation. 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 inferior solar conjunction - 18:41 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 and the Sun will appear at a separation of only 2°26', making Mercury 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 0.67 AU from the Earth, making it appear with its largest angular size. If it could be observed, it would measure 10.0 arcsec in diameter, whilst appearing completely unilluminated.

  • December 29 - New Moon - 06:55 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 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.

  • December 29 - Conjunction of the Moon and Mercury 04:55 UTC. The Moon and Mercury will share the same right ascension, with the Moon passing 1°45' to the north of Mercury. The Moon will be at mag -5.5, and Mercury at mag 1.6, 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 30 - Conjunction of the Moon and Pluto - 00:51 UTC. The Moon and 134340 Pluto will share the same right ascension, with the Moon passing 2°45' to the north of 134340 Pluto. The Moon will be at mag -7.2, and 134340 Pluto at mag 14.9, 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 through a pair of binoculars.

  • December 31 - Comet 45P/Honda-Mrkos-Pajdusakova at perihelion. Comet 45P/Honda-Mrkos-Pajdusakova will make its closest approach to the Sun, at a distance of 0.53 AU. For more information about its path across the sky, see In-The-Sky.org's ephemeris page for comet 45P/Honda-Mrkos-Pajdusakova.

Video courtesy Hubble Space Telescope

Sources: InTheSky (Dominic Ford)SeaSky

Featured image background credit: SolarSystemScope

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