This page provides some astronomical information on a monthly basis for those of you living in the United Kingdom. Timings are in GMT (Greenwich Mean Time) unless otherwise noted. York will be used as a representative location for the United Kingdom. Latest additions or updates are highlighted with a red border.
This month we have sections on:
Additional information on the phases of the Moon, the seasons, summer times, eclipses, chronological cycles and eras, religious calendars, the civil calendar and holiday dates in the United Kingdom can be found in HMNAO's Astronomical and Calendarial Sheet No. 105 for 2018. This is a pdf document for which a document reader can be downloaded by clicking on the Adobe Reader icon above.
↻ The last update to this page was made on Thursday, 2018 December 13 at 07:58:46 GMT.
The Winter Solstice for the northern hemisphere (or the Summer Solstice for the southern hemisphere) takes place on Friday December 21st at 22:23 GMT. The word "solstice" comes from the latin for Sun (Sol) and to stand still (sistere) and refers to the fact that the Sun has reached its most extreme declination south in the case of the Winter Solstice for the northern hemisphere. Put another way, the Sun has reached the smallest daily maximum altitude it can attain when due south in the northern hemisphere. For York, at local noon, the Sun reaches a maximum altitude of 12.7°.
An animated view of the Sun's disk over the last twenty-eight days is shown in the image on the left. North is at the top of the image and east is to the left. These images come from the Helioseismic and Magnetic Imager instrument on the NASA Solar Dynamics Observatory (SDO) satellite. More multi-wavelength data from the SDO can be found here.
The active region designated AR2730 has disappeared and the Sun is devoid of sunspots once more. The number of spotless days for 2018 has risen to 205, or 59% of the year so far, exceeding the total number of spotless days for 2017 by one hundred and one days. An irregular-shaped coronal hole lies in the central region of the southern hemisphere of the Sun. Solar winds from this feature are expected to reach the Earth on December 16th. Overall solar activity remains at very low levels.
The increasing number of spotless days heralds the coming of the solar minimum expected in 2019/2020. The decline in the number of sunspots is greater than expected. This could be the deepest solar minimum in more than a century. This phase of the solar cycle brings increased numbers of cosmic rays to the Earth, an increased frequency of "pink" aurorae and a slight dimming of the Sun of approximately 0.1% in terms of the total solar irradiance. A new satellite has been launched, TSIS-1, which will monitor the Sun over the next five years covering the whole of the upcoming solar minimum. Cooling and contraction of the Earth's upper atmosphere in response to the changes on the Sun due to the solar minimum also delayed the orbital decay of satellites such as the Chinese space station, Tiangong 1, which returned to Earth on April 2nd 2018 at 00:16 UTC. The Sun's magnetic field and solar winds provides some protection for the Earth from cosmic rays. A recent paper in the journal Space Weather claims that this solar minimum could see a rise in the number of cosmic rays reaching the Earth by as much as 30% due to the weakening magnetic field of the Sun and reduced levels of solar winds. This could mean an increased risk of radiation exposure for travellers on commercial airlines and possible changes to the climate.
NASA reported that a reversal of the Sun's magnetic field took place at the start of 2014 indicating that the maximum of solar cycle 24 had been reached. A plot of sunspot numbers, both observed and predicted versus time indicates that this solar maximum is more complex than had been previously predicted. The maximum is double-peaked in a similar manner to that of the previous maximum of 2001/2002. The individual peaks occurred in 2011 and 2014 with the latter being the larger of the two. However, sunspot numbers are significantly down on the predictions made for this maximum — indeed solar cycle 24 may be the weakest in the last 100 years or so i.e. since solar cycle 14. Assuming the start of 2014 was the beginning of the post maximum phase of solar cycle 24, we are now well into the decreasing phase of activity where individual energetic events can spawn some of the most powerful flares and coronal mass ejections of the cycle. The so-called Carrington event of 1859 is a good example of just what might be expected from this type of violent outburst. The next solar minimum, characterized by periods of many days without sunspots and flare activity, may occur in 2019 or 2020. It is likely to be a deep minimum with long periods without much sunspot or flare activity. Space weather will be dominated by solar winds and cosmic rays rather than sunspots and solar flares.
The sequence of Moon phases for this month and their designations are shown in the following animation:
|Moon phases for December 2018 are as follows:|
|New Moon||—||Friday December 7th at 07:20 GMT
|First Quarter||—||Saturday December 15th at 11:49 GMT|
|Full Moon||—||Saturday December 22nd at 17:49 GMT|
|Last Quarter||—||Saturday December 29th at 09:34 GMT|
The Moon is at apogee (i.e. furthest from the Earth) on Wednesday December 12th at 12:25 GMT when it is 405,177km from the Earth. It is at perigee (i.e. closest to the Earth) on Monday December 24th at 09:49 GMT when it is 361,061km from the Earth.
On Sunday December 9th, the Moon occults the planet Saturn, the first-magnitude planet in the constellation of Sagittarius. This occultation by a thin waxing crescent moon is visible from south-eastern Russia and the northern tip of China. This occultation is not visible from the United Kingdom.
Please follow the New Moon link above to find out more about our Crescent Moon Watch program which involves making sighting of the new crescent moon as early as possible after the instant of New Moon.
If you want to know what the Moon looks like now, try this USNO page generated by our colleagues in the Astronomical Applications Department at the US Naval Observatory in Washington.
There are five eclipses in 2018, two are total eclipses of the Moon and the remaining three are partial eclipses of the Sun. One total eclipse of the Moon is visible in the United Kingdom, namely that of 2018 July 27th. One partial eclipse of the Sun is also visible from the northernmost parts of the United Kingdom on 2018 August 11th.
A total eclipse of the Moon occurred on Wednesday January 31st 2018. It was visible in its entirety from Alaska, western Canada, the Hawaiian Islands, western Polynesia, Melanesia, Micronesia, most of Australia, New Zealand, eastern Indonesia, the Philippines, eastern China, Japan and eastern Siberia. Western parts of the United States, western China and India also saw the total phase of the eclipse. The eclipse ended just before moonrise in the United Kingdom so it was not visible in the United Kingdom. Photographs of this eclipse taken around the end of totality show the effect of atmospheric scattering (left-hand image – red colouration) and ozone in the Earth's stratosphere (right-hand image – turquoise colouration).
A partial eclipse of the Sun occurred on Thursday February 15th 2018. It was visible in its entirety from most of Antarctica except parts of eastern Antarctica including Enderby Land, American Highland and Wilkes Land, and the southern part of South America including Argentina and the southern half of Chile. This eclipse was not visible from the United Kingdom.
A partial eclipse of the Sun occurred on Friday July 13th 2018. It was visible from the easternmost part of Wilkes Land in Antarctica, the southern tip of New Zealand and the southernmost parts of South Australia and Tasmania. This eclipse was not visible from the United Kingdom.
A total eclipse of the Moon occurred on Friday July 27th 2018. This lunar eclipse exhibited the longest duration of totality of 103.6 minutes in the 21st century. It was visible in its entirety from the Indian Ocean region, westernmost China, India, the Middle East, central Asia, Turkey and the eastern half of Africa. Most of Australia, the Philippines, Indonesia, most of China, western Africa and most of Europe saw the total phase of the eclipse. Some of the total phase of the eclipse was visible from the United Kingdom as the Moon rose during the umbral part of the eclipse. In York, the Moon rose at 21:04 BST, approximately halfway between the start of the total phase at 20:30 BST and the middle of the total phase at 21:22 BST. The Moon rose in a totally-eclipsed state and we saw about three quarters of the total phase of the eclipse.
A partial eclipse of the Sun occurred on Saturday August 11th 2018. It was visible in its entirety from north-easternmost parts of Canada, Greenland, Iceland, northern Scotland, Scandinavia except Denmark, most of Russia except the south-western and eastern parts, and central Asia. In the United Kingdom, this eclipse was visible from the northernmost parts of Scotland, the Orkney Islands and the Shetland Islands as a very small partial eclipse with an obscuration of less than 1.8%. The eclipse lasted 30 to 40 minutes with maximum obscuration occurring at around 9:49 BST.
Further information on all the eclipses in 2018 can be found on the Eclipses Online web pages. This web site provides information on both solar and lunar eclipses in the period from 1501 CE to 2100 CE. Global circumstances of both solar and lunar eclipses are provided as well as local circumstances of the solar eclipses based on a gazetteer of approximately 1500 locations worldwide. Eclipses for next year, 2019, are also available.
Mercury is visible low in the south-eastern morning twilight sky during December, rising between one and two hours before the Sun. It reaches greatest western elongation on Saturday December 15th. Mercury brightens significantly from magnitude +1.7 at the start of the month to magnitude −0.5 in mid-December, fading slightly to magnitude −0.4 at the end of the month. It lies 1.9° south of the waning crescent moon on Wednesday December 5th, 6° north of Antares on Friday December 21st and 0.9° north of Jupiter on the same day.
Venus rises around four hours before the Sun and is a very conspicuous object in the south-eastern morning twilight sky. It reaches its greatest illuminated extent on Sunday December 2nd and is clearly visible as a crescent when viewed with binoculars. Venus fades somewhat from magnitude −4.9 at the start of the month to −4.7 at the end of December. It lies 4° south of the waning crescent Moon on Monday December 3rd.
Mars rises around four hours before sunset and is visible in the southern evening sky, moving from the constellation of Aquarius to Pisces at the end of the third week of December. It fades significantly from magnitude 0.0 at the start of the month to +0.4 at the end of December. Mars lies 0.04° north of Neptune on Friday December 7th, an excellent opportunity to see Neptune using binoculars, and lies 4.0° north of the waxing crescent moon on Friday December 14th.
Jupiter re-emerges into the south-eastern morning twilight sky in the middle of the month after its conjunction with the Sun on Monday November 26th. It lies in the constellation of Scorpius where it brightens slightly from magnitude −1.7 at the start of the month to −1.8 at the end of December. Jupiter lies 5° north of Antares on Thursday December 20th and lies 0.9° south of Mercury on Friday December 21st. This is a good opportunity to identify Mercury with either binoculars or the naked eye.
Saturn rises in the east south-eastern sky an hour or so after sunrise and is visible with difficulty in the south-western sky during evening twilight until mid-December. It lies in the constellation of Sagittarius where it remains at magnitude +0.5 for the remainder of 2018. Saturn lies 1.1° south of the waxing crescent moon on Sunday December 9th.
Uranus is visible for most of the night for observers using binoculars, rising in the east north-eastern sky in the early afternoon and setting around three hours after midnight. It moves from the constellation of Aries into Pisces on Monday December 3rd. Uranus is a blue-green object which fades slightly from magnitude +5.7 to +5.8 during the month. It lies approximately 1.3° east of the fourth magnitude star Omicron Piscium. This planet can also be glimpsed with the naked-eye under optimum conditions.
Neptune is visible for the first part of the night for observers using a small telescope, rising in the east south-eastern sky at around noon and setting in the late evening. It lies in the constellation of Aquarius approximately 2.1° to the east of the fourth magnitude star Lambda Aquarii. Neptune is a bluish object of magnitude 7.which can be visible with good binoculars under optimum conditions. However, please note, that it can be difficult to distinguish Neptune from other stellar objects of a similar magnitude.
Pluto lies in the north-eastern part of the constellation of Sagittarius. It rises around two hours before noon and is visible with larger amateur telescopes in the south south-western part of the sky during evening twilight, setting in the early-evening. Strictly speaking, this is a dwarf planet as it was demoted from the ranks of the "bona-fide" planets in 2006. I have to confess that I was one of those astronomers that voted for its demotion at the International Astronomical Union General Assembly in Prague in 2006! At magnitude +14.6, you will need a much more serious telescope to find this remote member of the Solar System.
The Geminid meteor shower is active from Tuesday December 4th to Monday December 17th and reaches a peak of activity on Friday December 14th at around 12:30 GMT. At its maximum, the shower exhibits as many as 120 meteors per hour for a day or so either side of the peak. This year, the observation of these bright, medium-speed meteors will be favoured in the second half of the night by the lack of moonlight. The waxing crescent moon will set at or before midnight on all of the optimum nights to observe the peak of the display. Geminids hit the atmosphere at about 35km/s, disintegrating at about 80 kilometres above the surface of the Earth. Nevertheless, this shower can be rich in fireballs (meteors brighter than the planet Venus) due to the rocky nature of its parent object. The radiant, the point in the sky from which the meteors appear to emanate, lies close to the first magnitude star Castor (α Geminorum) in the constellation of Gemini. Observations are normally best carried out between midnight and sunrise when the radiant is highest in the southern part of the sky. This shower is related to the asteroid or "rock comet" 3200 Phaethon making it one of only two showers not connected with a comet — the other shower being the Quadrantids which are visible next month. No other regular showers exhibiting significant numbers of meteors are active this month. Further information on these and other meteor showers occurring during 2018 can be found at the International Meteor Organization and their 2018 Meteor Shower Calendar.
It is worth noting that bright sporadic meteors and fireballs are possible at any time e.g. the fireball observed over many parts of England and Scotland on Saturday March 3rd 2012 at 21:40 GMT. Larger events, known as bolides, are rarer. Typically, this is a very bright fireball reaching an apparent magnitude of −14 or so, perhaps three times as bright as a full moon. Even rarer are the superbolides, events with apparent magnitudes of −17 or so, around 50 times brighter than the full moon. A recent example of a superbolide was the Chelyabinsk meteor of 2013 February 15th at 03:20 UTC which may have been a 20-metre diameter near-Earth asteroid.
Another loosely-related phenomenon is the re-entry of space debris from space vehicles and satellites whose orbits are decaying to the point where they burn up in the Earth's atmosphere. A couple of well-reported examples of this occurred at around 23:00 BST on Friday September 21st 2012 as well as the return of the GOCE satellite just after midnight on Tuesday November 12th 2013.
There are a number of comets around the sky at the moment. However, most of them require telescopic assistance to see them and some may be too far south in the sky to be seen by observers based in the United Kingdom. Here is a brief summary of the comets that may be accessible to observers with binoculars or small telescopes in the northern hemisphere.
The periodic comet 38P/Stephan-Oterma is visible with binoculars high in the sky after midnight in the constellation of Cancer for the first twelve days of December and spends the remainder of the month in the constellation of Lynx. The comet is a magnitude 6.7 object at the start of the month, potentially fading by about 0.8 magnitudes by the end of December. It reached perihelion on Sunday November 11th and will pass by the Earth at a distance of 0.8au on Monday December 17th.
A newly-discovered comet is just about visible in the south-western evening twilight sky. Comet C/2018 V1 Machholz-Fujikawa-Iwamoto is a magnitude 5.3 object lying in the constellation of Ophiuchus for the first five days of December. It then moves through Serpens Cauda and Scutum on its way to Sagittarius in the middle of the month when it disappears from our northern skies. It has quadrupled in brightness since its discovery on November 7th/8th but will fade during December to around tenth magnitude. C2018 V1 has both an ion tail and a dust tail visible with CCD imagery; the ion tail is made up of ionized carbon monoxide pointing away from the Sun and the dust tail is composed of debris from the comet following in its orbital path. This comet appears to be a first time visitor to the inner solar system making magnitude predictions somewhat problematic. It approached the Earth at a distance of 0.67au on Tuesday November 27th and will make a perihelion passage at 0.38au on Monday December 3rd. This comet exceeds the Bortle limit so it may not survive its passage through perihelion.
46P/Wirtanen is a short-period comet with an active nucleus a little over a kilometre wide. It will come to perihelion in the late evening of Wednesday December 12th and will then make a close approach to the Earth on Sunday December 16th at approximately 13:00 UT. This approach will be the 10th closest by any comet since 1950, at a distance of only 0.0775au (30 lunar distances or 11.6 million kilometres). At closest approach, it may reach magnitude 2.5. This means that the comet could be a somewhat greenish naked-eye object visible in the late-evening southern sky only three and half degrees away from the Pleiades open cluster in the constellation of Taurus just over a week before Christmas. At the moment, it is a magnitude 4.7 object in Cetus and is best viewed with binoculars. By mid-December, it could be as bright as magnitude 2.5. Please bear in mind that these estimates are integrated magnitudes over the whole comet. The closer the comet, the larger the area of sky it occupies. The coma or head of comet will look fainter than these estimates.
As it is reasonably favourably placed for both northern and southern hemisphere observers, it will be the subject of an international campaign to observe it. During October 46P/Wirtanen moved south in the constellation of Fornax; it then turned north at the end of the first week of November, passing through Cetus, Eridanus, back into Cetus. It then moves into Taurus on December 11th as it heads towards its closest approach with the Earth. The path of 46P/Wirtanen for the last couple of months of 2018 is shown in mapping from HMNAO's Comet Ephemeris Service and its path during December is shown here.
With a period of 5.4 years, this comet has been a regular visitor to the inner solar system since its discovery in January 1948 by Carl Wirtanen during a photographic proper motion survey at Lick Observatory. This comet is also associated with a very weak meteor shower, the Piscids, last visible in mid-December 2012 with a radiant between Pisces and the Great Square of Pegasus, The shower is active at the same time as the more prolific Geminids.
An image taken with a DSLR camera and wide angle lens on December 3rd gives you some idea of what the comet currently looks like. It is close to the limit of naked-eye visibility but easily visible with 7x50 binoculars. The coma is nearly twice the diameter of the full moon but sadly there is no clear evidence of a tail. Here are images taken on December 8th from the Czech Republic and December 9th from Norway.
If you want to look for the International Space Station (ISS) as it passes over your location, please have a look at the Heavens Above web site. Choose your observing location in the Configuration section and then select ISS in the Satellites section. The ISS is at least as bright as a first magnitude star and can approach the brightness of Venus. Similarly, if you want to look for the Chinese space station, Tiangong-1, you are too late! Tiangong-1 re-entered the Earth's atmosphere in an "uncontrolled manner" on April 2nd 2018 at 00:16 UTC over an uninhabited part of the central Pacific Ocean at longitude 164.3° west and 13.6° south after the loss of a telemetry link in 2016. Tiangong-2, the sole remaining Chinese space station orbiting the Earth is normally as bright as a third or fourth magnitude star. Predictions for it and other satellites may also be obtained from the Heavens Above web site.
Another satellite-related phenomena to look out for are the so-called "Iridium flares". These bright flashes of sunlight reflecting off the Iridium series of communication satellites can be seen at night and also occasionally during the daytime if they are bright enough. Predictions for the next seven nights can be obtained from the Heavens Above web site by setting your observing location in the Configuration section and then selecting Iridium Flares in the Satellites section.
The above image is a 30 minute forecast of the location and probability of auroral activity based loosely on a model developed at Johns Hopkins' Applied Physics Laboratory known as the Ovation Aurora Forecast model. It provides estimates of the energy per unit area on the Earth's atmosphere from observations of the solar wind and interplanetary magnetic field made by the Advanced Composition Explorer satellite in conjunction with empirical relationships derived from the Defense Meteorological Satellite Program. It shows where the aurora is most likely to be seen and how bright it is likely to be. The model generates a global estimate of power, called the Hemispheric Power, deposited into the atmosphere in gigawatts (GW). For powers of less than 20GW, little or no aurora may be visible. For powers of 20-50GW, you may need to be relatively close to the aurora to see it. For values above 50GW, the aurora should be easily observable, active and mobile. For values above 100GW, this is considered to be a significant storm where the aurora may be visible from hundreds of miles away. The current prediction is downloaded when you load this page. If you want to download the latest model, simply reload this page or hit F5. If you want to see the full-sized map, please click on the above image.
The above sky chart, generated from the Heavens-Above.com web site, shows what the night sky looks like at 22:00 GMT on Sunday December 16th from York. The night sky will look the same an hour later at 23:00 GMT at the beginning of the month and an hour earlier at 21:00 GMT at the end of the month. Please click on the chart to see a full-sized sky chart image. If you want to generate your own star chart for another combination of location, date and time, please have a look at the Heavens Above web site. Choose your observing location in the Configuration section and then select Sky Chart in the Astronomy section.
Rising and setting times for the Sun and Moon as well as the planets and the times of twilights for other locations in the United Kingdom can be obtained from HMNAO's Websurf web pages using the Rise, Set and Twilight Times option.
The actual times at which the Sun will just appear, or disappear, will depend on the difference of the altitudes of the observer and the local horizon and the actual refraction, which depends on the meteorological conditions along the light path. Differences of a minute or so from the tabulated times are to be expected.
For the drivers amongst you, the "Hours of Darkness", as defined by the Road Vehicle Lighting Regulations (1989), start half an hour after sunset and end half an hour before the following sunrise. Headlights should be used during the Hours of Darkness and sidelights in the half hour periods after sunset and before sunrise. These timings can also be obtained from HMNAO's Websurf web pages using the Rise, Set and Twilight Times option.
For the VFR (Visual Flight Rules) pilots amongst you, night, according to Statutory Instrument 2009 No. 3015, Civil Aviation, The Air Navigation Order 2009, Part 33 (Interpretation), Article 255(1), means "the time from half an hour after sunset until half an hour before sunrise (both times inclusive), sunset and sunrise being determined at surface level". In other words, the night time period starts at the beginning of the Hours of Darkness and finishes at the end of the Hours of Darkness.