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 Friday, 2021 April 16 at 18:19:04 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.
The active region AR2814 lies in the south-western quadrant of the Sun and continues to pose a threat for minor C-class solar flares. AR2814 is now composed of nearly a dozen or so moon-sized dark cores spread over a distance of about 75,000 km. Two new active regions are emerging in the southern hemisphere of the Sun, one close to the south-eastern limb and the other close to the centre of the disk. The total number of spotless days for 2021 remains at forty one, or 39% of the year so far. Solar winds are currently blowing with velocities of around 450 km/s and the planetary Kp geomagnetic activity index is likely to peak at 3 (quiet) today. Two coronal holes lie in the southern hemisphere of the Sun, one occupying the south polar region and the other halfway along the western part of the Sun's equator. Solar winds emanating from these features should reach the Earth on April 17th–18th. Minor G1-class geomagnetic storms are possible on April 17th which may bring auroral activity to the polar regions. 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 April 2021 are as follows:|
|Last Quarter||—||Sunday April 4th at 11:02 BST|
|New Moon||—||Monday April 12th at 03:31 BST
|First Quarter||—||Tuesday April 20th at 07:59 BST|
|Full Moon||—||Tuesday April 27th at 04:32 BST
The Moon is at apogee (i.e. furthest from the Earth) on Wednesday April 14th at 18:46 BST when it is 406,119 km from the Earth. It is at perigee (i.e. nearest to the Earth) on Tuesday April 27th at 16:22 BST when it is 357,378 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 Tuesday April 27th 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 Saturday April 17th, the Moon occults the planet Mars in the north-eastern part of the constellation of Taurus. This occultation by the waxing crescent moon is visible from most of central and eastern Africa, southern parts of the Middle East, India, South-East Asia, Indonesia and most of the Philippines. This occultation is not visible from the United Kingdom.
Ramadan, the ninth month of the Islamic calendar, when Muslims fast during daylight hours, starts with the sighting of the new crescent moon on or about Tuesday April 13th. Further information on the visibility of this month's crescent moon can be found here.
First Sighting of the New Crescent Moon: My sighting of the new crescent moon for this month which marks the beginning of Ramadan, the holy month of fasting for Muslims, was made at 20:37 BST on Wednesday April 14th from Ash Priors. The Moon was at an altitude of 17.9° and an azimuth of 275.0°. It was 6.3% illuminated, 65.1 hours old and lay at an elongation from the Sun of 30° east. The Moon appeared to be tilted over at an angle of approximately 45° in a clockwise direction. The observation was made after sunset when the Sun was 5.3° below the horizon. In all likelihood, the crescent could have been sighted earlier as the observation was hampered by substantial amounts of intermittent cloud. No sighting was made on Tuesday April 13th as intermittent cloud prevented a sighting from Ash Priors.
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 eastern morning twilight sky in the first ten days of the month and in the western evening twilight sky for the last few days in April. It is no longer visible as it reaches superior conjunction on Monday April 19th. Mercury brightens significantly from magnitude −0.5 at the start of the month to −1.1 by the end of the morning apparition. It fades significantly from magnitude −1.5 at the start of the evening apparition to −1.1 by the end of April. It is difficult to observe during the morning apparition as Mercury rises with the Sun and is best seen in the last few days of April, setting an hour or so after the Sun, as it moves towards its best evening apparition of the year during May.
Venus is still too close to the Sun to be observed, having reached superior conjunction on Friday March 26th. It will return to the evening sky during the first half of May for its best apparition of the year for northern hemisphere observers. It might be spotted in the west north-western evening civil twilight sky during late April.
Mars rises in the north-eastern sky nearly three hours after sunrise and sets between one and two hours after midnight in the north-western sky. It spends most of April in the constellation of Taurus, crossing into Gemini at the beginning of the last week of April. Mars continues to fade from magnitude +1.2 at the start of the month to magnitude +1.5 at the end of April. It lies 0.1° north of the waxing crescent moon on Saturday April 17th which will be seen as an occultation in certain parts of the world.
Jupiter becomes more prominent in the east south-eastern morning twilight sky as April progresses. It lies in the north-eastern part of the constellation of Capricornus for most of the month moving into the western part of Aquarius in the last week of April. Jupiter brightens somewhat from magnitude −2.0 at the start of the month to magnitude −2.2 at the end of April. Jupiter lies 4° north of waning crescent moon on Wednesday April 7th.
Saturn continues to emerge into the east south-eastern morning twilight sky during April. It lies in the central part of the constellation of Capricornus for the whole of the month and brightens slightly from magnitude +0.8 at the start of the month to magnitude +0.7 at the end of April. The Saturn lies 4° north of the waning crescent moon on Tuesday April 6th.
Uranus is visible with difficulty during the first couple of weeks of the month setting an hour or so after sunset. It then disappears from the evening twilight sky as it approaches conjunction with the Sun on Friday April 30th. It is a blue-green object which remains at magnitude +5.9 during the first part 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 11.4° north east of the fourth magnitude yellow giant star Torcular (ο Piscium). This planet can also be glimpsed with the naked eye under optimum conditions.
Neptune has been too close to the Sun to observe from the middle of February until the second week of April when it re-appears in the eastern morning twilight sky having reached conjunction with the Sun on Thursday March 11th. 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 9.8° 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 reappears 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 15.1° to the south west of Saturn in mid-April. 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 April Lyrids are active between Wednesday April 14th and Friday April 30th, peaking on Thursday April 22nd at around 14:00 BST. This shower normally yields rates of about 18 meteors per hour but the rate can occasionally reach 90 or so. The Lyrids are medium-swift meteors with brightnesses of around magnitude +2, similar to the brightness of the stars making up 'The Plough'. About a quarter of Lyrid meteors leave persistent trains but occasionally the shower produces very bright meteors called 'Lyrid Fireballs' capable of casting shadows for a split second or so with persistent smoky debris trails that last for minutes. The narrow peak of the shower, lasting from fifteen to sixty hours, is not well aspected this year due to the presence of moonlight — the first quarter moon occurs around 54 hours before the peak of the shower. The radiant, the point in the sky from which the meteors appear to originate, is on the Lyra / Hercules border (not too far from the blue-white first magnitude star Vega) and is high enough in the sky to observe from shortly before midnight onwards. The Lyrids are associated with comet C/1861 G1 Thatcher which has been observed at only one passage in 1861 as it has a period of 415 years. This shower was first recorded by Chinese observers in chronicles dating back to 687 BC. The Lyrid meteor shower has the distinction of being among the oldest of the known meteor showers having been observed for over 2,700 years.
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 2013 February 15th 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) makes its closest approach to the Earth on Friday April 23rd at a distance of 0.46 au when it could reach magnitude +8.5. At the beginning of April, the comet is a magnitude +9.1 object visible with small amateur-sized telescopes. C/2020 R4 (ATLAS) spends the first twelve days of the month in the constellation of Aquila and then moves into the neighbouring constellation of Ophiuchus for a single day, moving into Hercules for nine days then spending four days in each of Corona Borealis and Böotes. It is visible in the south-eastern pre-twilight sky during April, gaining in altitude as the month progresses. Here is a photograph of the comet taken from Austria on Sunday April 11th.
If you want to look for the International Space Station (ISS) as it passes over Taunton, please have a look at this 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. 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 Monday 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. Information for Tiangong-2, the sole remaining Chinese space station orbiting the Earth, can be found on this page. Tiangong-2 is significantly fainter than the ISS, normally as bright as a third or 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 Thursday April 15th 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 April 2021, the amount of daylight (measured from sunrise to sunset) increases from 12 hours 57 minutes at the start of the month to 14 hours 46 minutes at the end of the month. Total daylight (sunrise to sunset) for the month is 416 hours 15 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!