This page provides some astronomical information on a monthly basis for those of you living in the United Kingdom. Timings are in BST (British Summer 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 phases of the Moon, seasons, summer times, eclipses, chronological cycles and eras, religious holidays, the United Kingdom civil calendar and holiday dates can be found in HMNAO's Astronomical and Calendarial Sheet 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 September 20 at 08:17:17 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 Sun's disk has been devoid of active regions for the past six days. The total number of spotless days for 2018 is now 148, or 56% of the year so far, exceeding the total number of spotless days for 2017 by forty four days. The Earth is exiting a stream of solar wind emanating from a former coronal hole in the south-western quadrant of the Sun. A new coronal hole has appeared in the south-eastern quadrant of the Sun's disk. Solar winds emanating from this feature should reach the Earth on September 23rd or 24th. With the approach of the autumnal equinox so-called "cracks" or fissures in the Earth's magnetic field are likely to increase the probability of bright auroral activity due to the Russell-McPherron effect. Observers in northern Canada saw fine auroral displays on September 14th including pink aurora resulting from nitrogen molecules being excited at atmospheric altitudes of less than 100km. Observers in the polar regions should remain vigilant; they are best-placed to observe any auroral displays arising from any geomagnetic storm activity. 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 September 2018 are as follows:|
|Last Quarter||—||Monday September 3rd at 03:37 BST|
|New Moon||—||Sunday September 9th at 19:01 BST
|First Quarter||—||Monday September 17th at 00:15 BST|
|Full Moon||—||Tuesday September 25th at 03:52 BST|
The Moon is at perigee (i.e. closest to the Earth) on Saturday September 8th at 02:20 BST when it is 361,351km from the Earth. It is at apogee (i.e. furthest from the Earth) on Thursday September 20th at 01:53 BST when it is 404,876km from the Earth.
On Monday September 3rd, the Moon continues its current series of occultations of Aldebaran, the orange first-magnitude star in the constellation of Taurus. This occultation by the last quarter moon is visible from most of Greenland and northernmost parts of Canada. 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. This eclipse was not visible in Grove.
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 very low in the eastern morning twilight sky during the first week of September. It reaches superior conjunction on Friday September 21st rendering it invisible to all but the most specialist of observers. It brightens from magnitude −0.7 at the start of the month to magnitude −1.3 at the end of the first week of September. Mercury lies 1.0° north of Regulus on Wednesday September 5th.
Venus sets in the western south-western twilight sky around an hour or so after sunset. It achieves its greatest illuminated extent on Friday September 21st. Venus continues to move south in the sky limiting its visibility even though its magnitude brightens somewhat from magnitude −4.6 at the start of the month to −4.8 at the end of September. It lies 1.4° south of Spica on Sunday September 2nd and lies 10° south of the waxing crescent moon on Wednesday September 12th.
Mars is visible in the evening sky, moving in a prograde manner (eastwards) and travelling increasingly rapidly through the western part of Capricornus. It fades noticeably from magnitude −2.2 at the start of the month to −1.3 at the end of September. Mars lies at a declination of between −26° and −24° for most of the month retaining its low altitude in the sky, rising an hour or so before sunset in the south-eastern part of the sky. It lies 5° south of the waxing gibbous moon on Thursday September 20th.
Jupiter can be seen low in the south south-western sky during evening twilight and sets a couple of hours after sunset in the west south-western sky. Jupiter will remain in the constellation of Libra for much of 2018. It fades slightly from magnitude −1.9 at the start of the month to −1.8 at the end of September. Jupiter lies 4° south of the waxing crescent moon on Friday September 14th.
Saturn rises in the south-eastern sky during the mid-afternoon and is visible in the southern sky in evening twilight. It lies in the constellation of Sagittarius where it will remain for the remainder of 2018. Saturn fades slightly from magnitude +0.4 at the start of the month to +0.5 at the end of September. It lies 2° south of the waxing gibbous moon on Monday September 17th.
Uranus is visible for most of the night for observers with binoculars. It rises in the east north-eastern sky around an hour or so after sunset in the constellation of Aries, approximately 4.1° north east of the 4th magnitude star Omicron Piscium. Uranus is moving towards opposition on October 24th. Uranus is a blue-green object, having a magnitude of +5.7 for the whole of September. This planet can also be glimpsed with the naked-eye under optimum conditions.
Neptune is visible all night long for observers with a small telescope. It rises in the eastern sky around sunset as it moves towards opposition on Friday September 7th. Neptune lies in the constellation of Aquarius approximately 3.1° to the east of the 4th magnitude star Lambda Aquarii. It is a bluish object whose magnitude remains at +7.8 for the whole of September. It 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 having risen during the late-afternoon. It is visible with large amateur-sized telescopes in the southern part of the sky after twilight. 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! At magnitude +14.6, you will need a much more serious telescope to find this remote member of the Solar System.
The rarely-spotted Zodiacal Light is best seen in the half hour or so before astronomical twilight starts in the morning or in the half hour or so after astronomical twilight ends in the evening. It is best seen when the ecliptic, the path the Sun takes in the night sky, is at a steep angle to the horizon. In northerly latitudes, this occurs in the western evening post-twilight sky in February and March and the eastern morning pre-twilight sky in September and October. The Zodiacal Light appears as a large, softly radiant pyramid of light with its base near the horizon and its axis centred on the Zodiacal constellations. It appears to be about as bright as the Milky Way, consequently a dark, unpolluted sky without haze is essential to see this phenomenon. Beware, it can easily be confused with twilight itself. In the photograph, the Zodiacal Light is on the left and the Milky Way is on the right. For York, astronomical twilight starts in the morning at around 03:55 BST at the beginning of the month and at 05:05 BST at the end of the month. The cause of this so-called "false dawn" is sunlight reflecting of a lens-shaped cloud of dust in the plane of the inner solar system.
There are no significant meteor showers active during September. The next shower exhibiting moderate numbers of fast meteors with long trains is the Orionids at the end of the third week of October. 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 21P/Giacobini-Zinner is visible with small binoculars from U.K. skies as a 7th magnitude object in the constellation of Auriga for the first two weeks of September. It then moves rapidly though parts of Taurus, Gemini and Orion and spends the last week of the month in Monoceros. It reaches perihelion on Monday September 10th and passes the Earth at a distance of 0.39au on Tuesday September 11th.
the periodic comet 38/P Stephan-Oterma is visible with a small telescope in the south-eastern morning twilight sky in the constellation of Orion. It is a 9th magnitude object at the start of the month, potentially brightening by a magnitude or so by the end of September. It reaches perihelion on Sunday November 11th.
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 BST on Saturday September 15th 2018 from York. 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 22:00 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 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.