This page provides some astronomical information on a monthly basis for those of you living in the Taunton area. Timings are in BST (British Summer Time) unless otherwise noted. 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. 108 for 2021. This is a pdf document for which a document reader can be downloaded by clicking on the Adobe Reader icon above.
This web page can also be accessed from outside the UK Hydrographic Office on http://astro.ukho.gov.uk/nao/taunton.html.
↻ The last update to this page was made on Tuesday, 2021 May 11 at 14:32:02 BST.
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.
Active region AR2822 lies in the north-eastern quadrant of the Sun. This multi-cored feature has already been associated with a number of coronal mass ejections over the past several days. Indeed, it produced an M3.9 class solar flare on Friday May 7th at 19:04 UT, the strongest flare of the new Solar Cycle 25. A pulse of ultraviolet and X-ray radiation ionized the upper layers of the Earth's atmosphere causing a shortwave radio blackout over the Americas. Ham radio operators, aviators and mariners might have noticed unusual propagation conditions at frequencies below 30 MHz between 19:00 UT and 19:20 UT. Indeed, radio transmissions at below 15 MHz were temporarily extinguished. However, the coronal mass ejection (CME) associated with this flare will miss the Earth. AR2822 continues to pose a threat of producing strong M-class solar flares as it turns towards the Earth, making any future activity geoeffective. A new active region has appeared in the south-eastern quadrant of the disk designated AR2823. This is a single spot with the potential for limited solar flare activity. Magnetic fields in the southern hemisphere of the Sun erupted on May 9th. A solar filament hurled another slow-moving CME into space, directed towards the Earth. Minor G1-class geomagnetic storms are possible on May 12th–13th when the CME arrives. The total number of spotless days for 2021 remains at forty six, or 35% of the year so far. Solar winds are currently blowing with velocities of around 360 km/s and the planetary Kp geomagnetic activity index is likely to peak at 2 (quiet) today. A new, narrow coronal hole lies in the centre of the visible disk of the Sun. Solar winds emanating from this feature could reach the Earth on May 13th–14th.The overall amount of solar activity remains at very low levels.
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 the solar maximum of Solar Cycle 24 was more complex than had been previously predicted. The maximum was 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 were significantly down on the predictions made for the maximum — indeed Solar Cycle 24 may be the weakest in the last 100 years or so i.e. since Solar Cycle 14.
The declining 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. TSIS-1 was launched on December 15th 2017, which will monitor the Sun over a five-year period covering the whole of the current 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 Monday April 2nd 2018 at 00:16 UTC. The Sun's magnetic field and solar winds provide 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.
During the post maximum phase of the solar cycle individual energetic events can spawn some of the most powerful flares and coronal mass ejections of the cycle. The so-called Carrington event on September 1st–2nd 1859 during Solar Cycle 10 is a good example of just what might ensue from this type of violent outburst. On 2020 September 15th NASA and NOAA announced that a minimum of the Sun's activity had been reached in December 2019 bringing to an end the old Solar Cycle 24. Predictions are that the new Solar Cycle 25 will be a weak one, similar to its predecessor, peaking in 2025. 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 flare activity.
The sequence of Moon phases for this month and their designations are shown in the following animation:
|Moon phases for May 2021 are as follows:|
|Last Quarter||—||Monday May 3rd at 20:50 BST|
|New Moon||—||Tuesday May 11th at 20:00 BST
|First Quarter||—||Wednesday May 19th at 20:13 BST|
|Full Moon||—||Wednesday May 26th at 12:14 BST
'Flower Moon' / Largest in 2021
The Moon is at apogee (i.e. furthest from the Earth) on Tuesday May 11th at 22:53 BST when it is 406,512 km from the Earth. It is at perigee (i.e. nearest to the Earth) on Wednesday May 26th at 02:50 BST when it is 357,311 km from the Earth.
The combination of the Moon being close to perigee and the phase of the Moon being either new or full (i.e. the Sun, Earth and Moon are in alignment) as it is around Wednesday May 26th and shortly thereafter leads to 'perigean (or proxigean)' spring tides i.e. spring tides with a tidal range slightly larger than those of normal spring tides.
On Wednesday May 12th, the Moon occults the planet Venus in the central part of the constellation of Taurus. This occultation by the thin waxing crescent moon is visible from most of New Zealand, eastern Polynesia, Easter Island and the southern central Pacific Ocean region. This occultation is not visible from the United Kingdom.
The festival of Eid al-Fitr, when Muslims celebrate the end of the fasting month of Ramadan, starts with the sighting of the new crescent moon on or about Wednesday May 12th or Thursday May 13th. Further information on the visibility of this month's crescent moon can be found here.
Please follow the New Moon link above to find out more about our Crescent Moon Watch program which involves making a sighting of the new crescent moon as early as possible after the instant of New Moon each month.
The term 'Supermoon' was coined in 1979 by astrologer Richard Nolle. He defined it as 'a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit', without explaining why the 90% figure was chosen. As the Moon's orbit is elliptical, not circular, there is a point in its orbit where it is closest to the Earth (perigee) and another one where it is furthest away from the Earth (apogee) and these perigee and apogee distances change somewhat from one orbit to another. In the period between 1850 and 2050, perigee distances for the Moon range from 356,375 km to 370,355 km while apogee distances range from 404,055 km to 406,710 km. Using Nolle's criterion, on average, a full moon occurring within 367,607 km of the Earth will be a supermoon.
The closest full moons occur on average in cycles of just over a year as 14 lunar months or lunations is only 2.7 hours longer than the time taken for 15 returns to perigee. The full moon of 2021 March 28th takes place at a distance of 362,174 km, 35.5 hours before perigee. The full moon of 2021 April 27th takes place at a distance of 357,616 km, 11.8 hours before perigee. The full moon of 2021 May 26th takes place at a distance of 357,461 km, 9.4 hours after perigee. The full moon of 2021 June 24th takes place at a distance of 361,560 km, 32.8 hours after perigee. The March and June full moons are marginal supermoons and, by some, may not be classed as supermoons. The full moons of April and May are supermoons by most, if not all, criteria. Within this four month period of 2021, all the full moons take place at distances of less than 362,200 km from the Earth. We might say that the supermoons of April 27th and May 26th are more super than the other two supermoons as they take place at distances of less than 357,700 km from the Earth. However, they do not make the list of the fifteen closest full moons in the interval 1850–2050 given below.
|The Fifteen Closest Full Moons: 1850–2050|
The four closest full moons in the 21st century will take place on 2034 November 25th at 22:32 UT at a distance of 356,446 km, 2052 December 6th at 07:18 UT at a distance of 356,426 km, 2070 December 17th at 16:05 UT at a distance of 356,463 km and 2098 January 17th at 10:36 UT at a distance of 356,461 km. Perhaps these will be known as 'Ultimoons'!
Many media articles will mention that the Moon will be 14% bigger and 30% brighter than when the full moon occurs furthest from the Earth or 7% bigger and 15% brighter than average. A nice illustration of this can be seen on the Astronomy Picture of the Day site. As a result of these differences, you might expect to see a significantly bigger and brighter Moon but this is not the case. The transition between an apogee full moon and a perigee full moon takes place over seven lunar cycles so the apparent changes in size from one full moon to the next are only perhaps 2% in apparent size and 3% in apparent brightness. These changes are more difficult to detect. Indeed, discerning changes in the size of the Moon is even more difficult to perceive when the Moon is close to the horizon due to the so-called 'Moon Illusion'. On a given night, the rising or setting Moon will appear larger than when it is high in sky. There is no proper explanation for this perceived difference but it may be related to the presence of perceptual cues for the eye near the horizon which are missing for an object much higher in the sky.
Is the supermoon just another piece of media hype? Have you also noticed the increasing use of the term 'Micromoon' for the smallest full moon in a given period of time? Neil de Grasse Tyson, the director of the Hayden Planetarium in New York, has suggested that supermoons are indeed over-hyped. 'I don't know who first called it a Supermoon' he told StarTalk radio. 'I don't know, but if you have a 16-inch pizza, would you call that a super pizza compared with a 15-inch pizza?'. Enough said ...
There are four eclipses visible from the Earth during 2021 — two lunar eclipses, one total and one partial and two solar eclipses, one annular and one total. Parts of two of the eclipses are visible from the United Kingdom, namely the partial phase of the annular eclipse of the Sun and some of the partial eclipse of the Moon. The total eclipses of the Sun and Moon are not visible from the United Kingdom.
A total eclipse of the Moon occurs on Wednesday May 26th 2021. It is visible in its entirety from south-westernmost Alaska, the Aleutian Islands, the Hawaiian Islands, Polynesia, the central Pacific Ocean region, New Zealand, Melanesia, Micronesia, central and eastern Australia and parts of Antarctica. Parts of the eclipse are visible from the Americas except north-eastern Canada and eastern parts of South America, Indonesia, the Philippines, Japan, eastern Asia, north-easternmost Russia and the eastern half of the Indian Ocean. The eclipse begins at 08:46 UT and ends at 13:51 UT. The Moon enters the umbral shadow at 09:45 UT. Totality begins at 11:10 UT and ends at 11:28 UT. The Moon leaves the umbral shadow at 12:53 UT. The eclipse is not visible from the United Kingdom.
An annular eclipse of the Sun occurs on Thursday June 10th 2021. It is visible as a partial eclipse from the north-eastern part of North America, the Arctic Ocean, most of Greenland, Iceland, northern Europe (including the British Isles), Scandinavia, most of Russia, Mongolia and most of China. The path of annularity begins over central Ontario and crosses over north-western Quebec, the southern part of Baffin Island, the north-western part of Greenland, the North Pole (for the only time this century) and the north-eastern part of Siberia. The eclipse begins at 08:12 UT and ends at 13:11 UT. The annular phase starts at 09:50 UT and ends at 11:33 UT. The maximum duration of annularity of 3m 48s takes place at 10:42 UT over the sea between Ellesmere Island and north-western Greenland. From Taunton, the partial eclipse starts at 10:04 BST and ends at 12:18 BST. The maximum obscuration occurs high in the south-eastern sky at 11:08 BST when 21.4% of the Sun is obscured.
A deep partial eclipse of the Moon occurs on Friday November 19th 2021. It is visible in its entirety from most of North America except the easternmost parts, Mexico, the eastern and central Pacific Ocean regions and north-eastern parts of Russia. Parts of the eclipse are visible from Scandinavia, the British Isles, Iceland, South and Central America, Australasia, Japan, the Philippines, most of Indonesia, eastern and northern Asia. The eclipse starts at 06:00 UT and ends at 12:06 UT. The umbral phase of the eclipse starts at 07:18 UT and ends at 10:47 UT. The maximum of the eclipse occurs at 09:03 UT with a magnitude of 0.978. The eclipse is visible in part from the United Kingdom. From Taunton, the partial eclipse starts at 06:00 UT and ends at 07:35 UT at moonset.
A total eclipse of the Sun occurs on Saturday December 4th 2021. It is visible as a partial eclipse from Antarctica, the South Atlantic Ocean, the southernmost part of South Africa, the South Indian Ocean, Tasmania and the southernmost part of Australia. The path of totality starts approximately 450 km to the east of the Falkland Islands, crosses the Weddell Sea and the Ronne Ice Shelf, Ellsworth Land and ends over the Amundsen Sea, approximately 500 km from the coast of western Antarctica. The eclipse starts at 05:29 UT and ends at 09:38 UT. The total phase of the eclipse starts at 07:00 UT and ends at 08:07 UT. The maximum duration of totality is 1m 57s at 07:33 UT over the Ronne Ice Shelf in western Antarctica. The eclipse is not visible from the United Kingdom.
Further information on all the eclipses in 2021 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, 2022, are also available.
Mercury can be observed in the western evening twilight sky at the end of civil twilight throughout May. It is at its best apparition for the year for northern observers during May, gaining in altitude until the middle of the month and then dropping back towards the horizon by the end of May. Mercury fades significantly from magnitude −1.1 at the start of the month to +2.8 by the end of May. It lies 8° north of Aldebaran on Tuesday May 11th and 2° north of the waning gibbous moon on Thursday May 13th. Mercury reaches greatest eastern elongation on Monday May 17th and lies 0.4° south of Venus on Saturday May 29th when Venus will be six magnitudes brighter than Mercury.
Venus is still close to the Sun at the start of May making observation difficult. It lies in the western evening twilight sky before starting its best apparition of the year for northern hemisphere observers. The elongation of Venus grows from 9° to 17° as the month progresses as its altitude increases. It fades slightly from magnitude −3.9 at the start of the month to −3.8 by the end of May. Venus lies 0.7° north of the waxing crescent moon on Wednesday May 12th which will be seen as an occultation in the southern Pacific Ocean region. It lies 6° north of Aldebaran on Monday May 17th and lies 0.4° north of Mercury on Saturday May 29th when Venus will be six magnitudes brighter than Mercury.
Mars rises in the north-eastern sky about three hours after sunrise and sets about an hour or so after midnight in the north-western sky. It spends the whole of May in the constellation of Gemini. Mars fades somewhat from magnitude +1.5 at the start of the month to magnitude +1.7 at the end of May. It lies 1.5° south of the waxing crescent moon on Wednesday May 16th and lies not too far away from Castor and Pollux at the end of May.
Jupiter becomes more prominent in the east south-eastern morning twilight sky as May progresses. It lies in the central part of Aquarius for the whole of May. Jupiter brightens somewhat from magnitude −2.2 at the start of the month to magnitude −2.4 at the end of May. Jupiter lies 5° north of waning crescent moon on Tuesday May 4th.
Saturn continues to emerge into the south-eastern morning twilight sky during May. It lies in the central part of the constellation of Capricornus for the whole of the month and brightens slightly from magnitude +0.7 at the start of the month to magnitude +0.6 at the end of May. Saturn lies 4° north of the last quarter moon on Monday May 3rd and lies 4° north of the waning gibbous moon on Monday May 31st.
Uranus reappears low in the east north-eastern morning twilight sky late in May after reaching conjunction with the Sun on Friday April 30th. It is a blue-green object which remains at magnitude +5.9 for the whole of the month. Uranus lies in the south-western part of the constellation of Aries where it remains for the rest of the year. It is approximately 5.2° north west of the fourth magnitude A9 giant star 87 Ceti (μ Ceti). This planet can also be glimpsed with the naked eye under optimum conditions.
Neptune lies in the eastern morning twilight sky rising one to two hours before the Sun. It lies in the north-eastern part of the constellation of Aquarius where it will remain for the rest of the year. Neptune is approximately 11.0° to the north east of the third magnitude red-giant star Hydor (λ Aquarii). It is a bluish object of magnitude +7.9 for most of the month. Neptune is a bluish object normally visible with good binoculars under optimum conditions although it can also be difficult to distinguish Neptune from other stellar objects of a similar magnitude.
Pluto lies low in the south-eastern morning twilight sky for observers with larger telescopes. It lies in the north-eastern part of the constellation of Sagittarius about 16.9° to the south west of Saturn in mid-May. Strictly speaking, this is a dwarf planet which was demoted from the ranks of the 'bona-fide' planets at the 2006 International Astronomical Union General Assembly in Prague. At magnitude +14.8, you will need a much larger telescope to find this remote member of the Solar System.
The Eta Aquariids are active between Monday April 19th and Friday May 28th, peaking on Thursday May 6th at around 04:00 BST. They are best seen from tropical and southern latitudes but from northern latitudes they can be seen in a short window as the radiant rises above the eastern horizon in the pre-dawn sky at the end of the first week of May. It has to be said that the peak of this shower is more of an extended plateau of activity lasting several days centred on the maximum. This shower exhibits a variable rate of around 30 meteors per hour, occasionally peaking as high as 85 meteors per hour. The shower is not affected by moonlight this year as the maximum occurs three days after last quarter moon. However, the shower is likely to be affected by the increasing morning twilight glow. The meteors are often swift and bright with long, persistent trains. This shower is loosely connected with Comet 1P/Halley, having separated from the comet hundreds of years ago.
No other significant meteor showers visible from our latitudes are active this month. Further information on meteor showers can be found at the International Meteor Organization and their 2021 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 Friday 15th February 2013 at 03:20 UTC which may have been a 20-metre diameter near-Earth asteroid.
A fireball was seen over a significant fraction of the United Kingdom and northern Europe on Sunday February 28th at 21:54 UT lasting approximately 3.5 seconds. It was estimated to be a magnitude −9 fireball which generated a sonic boom as it fell. Fragments of the object may have impacted the Earth in the area north of Cheltenham in Gloucestershire. Its solar-system point of origin may lie in the asteroid belt between Mars and Jupiter. It has since been reported that at least part of the carbonaceous chondrite fell at a property in Winchcombe in Gloucestershire making it the first UK-based meteorite find in the past 30 years. The significance of this type of dark stony meteorite lies in the fact that its chemistry is similar to that of the early Solar System.
A loud sonic boom was heard at 14:58 UT on Saturday March 20th 2021. It rattled windows and shook homes for about 20 to 30 seconds and was heard over large tracts of Dorset, Devon, Somerset and Jersey. An explosion, an earthquake, thunder and a sonic boom from an RAF aircraft have all been ruled out. The culprit appears to be a daylight fireball or bolide which may have landed in the Bristol Channel. It has been photographed and may also have been detected on a Eumetsat weather satellite image. To be visible in daylight, the meteor must have been of a significant size, large enough for debris to have reached the ground. Its track through the atmosphere may be revealed by analysis of photographic material.
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 brighter than magnitude +11.0 that may be accessible to observers with binoculars or small telescopes in the northern hemisphere.
C/2020 R4 (ATLAS) made its closest approach to the Earth on Friday April 23rd at a distance of 0.46 au when it reached magnitude +8.5 after a surge in brightness of a magnitude in late April. At the beginning of May, the comet is a magnitude +10.5 object just visible with small amateur-sized telescopes. C/2020 R4 (ATLAS) spends the first six days of the month in the constellation of Canes Venatici and then moves into the neighbouring constellation of Coma Berenices for five days, moving into Ursa Major for two days then spending the remainder of the month in the constellation of Leo. It is visible in the south-western early evening sky during May, gradually moving into the evening twilight as the month progresses. Here is a photograph of the comet taken from Austria on Sunday April 11th. The comet will fade rapidly to around 14th magnitude by the end of May.
Strictly speaking, this phenomenon is an atmospheric one rather than a truly astronomical one. Nonetheless, living in the United Kingdom, we are well placed to see this unusual spectacle during the shorter nights of the summer months, particularly in June and July.
These tenuous cloud-like structures are composed of ice-coated particles at an altitude of around 80 km in the mesosphere, approximately four times higher than the limiting altitude of cirrus cloud. Created by water vapour freezing around meteor smoke in the upper atmosphere, their altitude means that they appear silvery-blue in colour against the darker twilight sky when the Sun lies between 6° and 16° below the horizon.
Noctilucent or 'night shining' Cloud is normally seen between 10° and 20° above the northern horizon exhibiting a range of forms — perhaps the most common is the 'herring-bone' pattern. Normal visibility limits are mid-May to mid-August, peaking around the time of the Summer Solstice. More information, including the facility to report your sightings, can be found at the Noctilucent Cloud Observers' Homepage.
A word of warning; displays are unpredictable and more frequently seen from the northern half of the United Kingdom. Nevertheless, observations have been submitted by observers living in this locality e.g. from Exeter and Castle Cary.
A short animation of a bright noctilucent cloud display observed in the north-western sky from Selsey Bill during the evening twilight on Monday July 15th 2008 by The Sky at Night's Pete Lawrence is well worth a look. A photograph demonstrating that these clouds can be seen from southern parts of the United Kingdom was taken by D. Tate in Castle Cary in the early hours of Monday June 10th 2013.
If you want to look for the International Space Station (ISS) as it passes over Taunton, please have a look at the predictions page on the Heavens Above web site. The ISS is at least as bright as a first magnitude star and can approach the brightness of Venus under favourable conditions. Similarly, if you want to look for the core module of the new, third generation Chinese space station, Tianhe-1, predictions for this 'under-construction' space station can be found on this page. This module, the first of three parts, was launched on Thursday April 29th 2021. Tianhe-1 is significantly fainter than the ISS, normally about as bright as a third of fourth magnitude star. Predictions for other satellites may also be obtained from the Heavens Above web site.
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 might 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 20-50 GW, you may need to be relatively close to the aurora to see it. For values above 50 GW, the aurora should be easily observable, active and mobile. For values above 100 GW, 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 press 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 BST on Sunday May 16th 2021 from Taunton. The night sky will look the same an hour later at 23:00 BST at the beginning of the month and an hour earlier at 21:00 BST 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 Taunton for another date and/or time, please follow this link.
In May 2021, the amount of daylight (measured from sunrise to sunset) increases from 14 hours 48 minutes at the start of the month to 16 hours 13 minutes at the end of the month. Total daylight (sunrise to sunset) for the month is 482 hours 51 minutes.
start and end times of civil, nautical and astronomical twilights.
|h m||h m||h m||h m||h m|
|** ** No phenomenon that day|
|PLEASE NOTE: These times are in Greenwich Mean Time (GMT) except between 01:00 GMT on March 28th and 01:00 GMT on October 31st when the times are in BST (British Summer Time) which is one hour in advance of GMT. Times given in red are in BST.|
The timings in the table above should be accurate to within 1–2 minutes inside the red circle superimposed on the map shown on the left.
Rising and setting times for the Sun, Moon and planets and times of twilights for other locations 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 between 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 in 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 pilots amongst you, night, according to Statutory Instrument 2016 No. 765, The Air Navigation Order 2016, Schedule I (Interpretation), Article 2, 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. In the United States, the Federal Aviation Administration (Federal Aviation Regulations, Section 1.1) defines night as the time between the end of evening civil twilight and the beginning of morning civil twilight as published in the American Air Almanac, converted to local time. Sunset to the following sunrise can also be defined as night in the United States as well as one hour after sunset to one hour before sunrise. By the way, flying in a total eclipse of the Sun does not count as night flying!