The Aurora Section encourages the observation of the aurora, the recruitment and training of observers, the collection, analysis and reporting on the occurrences of auroral events. The present observer network comprises members of the BAA or other astronomical associations and societies, individual observers and professional scientists. Observations are collected from Canada, the United States, Iceland, the British Isles and European countries. The co-ordination of observing in the southern hemisphere is carried out by the Royal New Zealand Astronomical Society Aurora Section.
Our Section investigates the behaviour of the mid latitiude storm aurora as the polar auroral oval expands during periods of active conitions. The orginal reports as received from observers are placed in the archives of Aberdeen University, Scotland and the details thereof are the subject of annual reports and techincal papers published in the BAA Journal and in the "Marine Observer" as published by the British Meterological Office.
Although artificial earth satellites can monitor auroral characteristics and behaviour, there is still good reason for the observation and recording of the aurora by ground based observers. This is because records of auroral activity can be traced back through the Middle Ages to Greek and Roman times.
The Aurora Section set up a specialist magnetometery group to encourage members to construct magnetometers and measure variations in the earth's magnetic field related to auroral activity. The simple suspended magnet instrument read by eye is used to detect if the magnetosphere is disturbed and auroral conditions are likely to develop. The magnetoresistive magnetometer is an automatic self recording instrument measuring variations in the direction of the horizontal field component. The fluxgate magnetometer is used automatically to record variations in the strength of the horizontal field component. Where weather conditions and street lights prevent observation of the aurora, the study of magnetic storms is a satisfying pursuit in itself.
Auroral activity causes chages in the ionosphere that can cause absorbtion of radio signals in high frequency but can extend the VHF signal range from transmitter to more distant receivers by using the auroral ion clouds virtually as a reflector. Radio auroral effects are made use of in studies by amateur radio operators. Section members interested in reporting on radio aurorae often combine these studies with magnetic observations. As the particles causing the visible aurora are different from those causing radio aurora, the presence of one need not mean the existence of the other.
The Section also observes the noctilucent clouds (NLC) that are visible in the summer months -generally the period from May to August- in the northern and southern hemisphere's. The clouds appear at a height of about 85km and are visible when the sun is between 6 and 16 degrees below the horizon. The techniques to observe the clouds are identical to those used with the aurora hence Section members are well placed to make observations for the assistance of atmospheric scientists, who have asked us for our assistance. In this instance there exists a Canadian network of observers, there is also a good network of observers in Finland with whom we co-operate while other European countries send their observations to us.
The following is a simplified description of auroral phenomenon which it is hoped will assist beginners. "Aurora" is the Latin word for dawn, and "Aurora Borealis" means the northern dawn -commonly referred to as the "northern lights". Conversly, "Aurora Australis" means the southern dawn for our southern hemisphere counterparts. At mid-latiutudes here in the U.K. -in it's simplest form- the aurora may on occasion be seen in the night sky as a glow low down on the northern horizon.
Auroral light is generated by the excitation of atmospheric atoms and molecules from their ground state due to the collisions between the incoming charged particles of the solar wind -chiefly electrons- and the previously mentioned atmospheric constituents. The excited atoms of the atmosphere then "give up" the energy obtained in these collisions in the form of visible light. The normal colours observed in the visible aurora range from green to red, although sometimes white and occasionally yellow or blue have been reported. The colours depend on the altitude, whether the atmospheric particles are nitrogen [N] or oxygen [O[ and the energy of the incoming charged particles.
The polar aurora is a permanent oval of auroral activity surrounding the magnetic pole in each hemisphere. The polar oval is roughly some 15 degree's of latitude from the pole on the dayside and 20 degree's of latitude from the pole on the nightside of the earth. The ovals remain fixed in space relative to the Sun-Earth line and the earth rotates under the ovals. The auroral zones are the locations on the earth's surface where the aurora is most frequently seen and are of course the regions swept by the ovals as the earth rotates.
During the period when the earth's magnetic field is quiet, the ovals remain in position. When the Sun is active the earth's magnetic field is disturbed by encountering clouds or streams of high speed solar wind particles and by associated magnetic fields. This can cause the auroral oval to expand both poleward and towards the equator, so that this storm aurora can be seen in mid-latitudes and in the U.K. The stronger the disturbance, the stronger and further south -towards lower latititudes- will the auroral display will occur.
Their are two basic types of auroral disturbance. There are those generated by transient or explosive activity on the visible surface of the Sun, typically solar flares, the frequency of which tends to increase or decrease according to the 11 year sunspot cycle. The most violent of these storms can happen infrequently at any time in the sunspot cycle, and if intense, can cause the aurora to be seen in the tropics. A full auroral storm can degin with a glow on the horizon from which one or more homogeneous arcs of light may develop. Rays like searchlight beams may then reach up from the arcswhich may then thereafter twist into bands. If the aurora then spreads south above the observer the rays may then be seen to converge at -or from- a central point overhead to to form a pattern called a corona. The storm may then dissolve, and patches of light may be seen in various parts of the sky. During the peak of the storm, movement of the forms mat be evident, including horizontal translation of rays, flaming, flickering, vertical movement of light through fixed forms. After the storm has died down it may repeat itself an hour or so later.
The second basic form of aurora is generated by the continuous streams of particles emanating from the active regions of the sun that spray the earth each time the sun rotates. Typical regions are the coronal holes which are most active in the declining years of the sunspot cycle so that this type of aurora is most frequent after sunspot maximum. Such aurorae are quieter in form, may repeat themselves for several nights on end and then recur 27 days later after on rotation of the sun. Recurrences can take place over many months until the solar feature causing the particle stream disappears. The quite aurorae do not penetrate so far south and in the U.K. are generally seen only in the North of Scotland and the Northern Isles. Only glows, quiet homogeneous arcs and occasionally rays may be seen. Sometimes observers may see short rays for a period of minutes only, and these may be the tops of rays forming part of a storm to the north below the observers horizon.
The base of an auroral arc normally lies at a height of approximately 105km above the surface of the earth so that the curve of the arc relects the curvature of the earth's surface. During intense storms, the arc may be forced down to 80km, and below which, the base of the arc may be fringed with a red colouration. In the height range of 80km to 240km the aurora is generally green in colour. From 240km to 600km the colour is red, but should a long ray reach out beyond the earth's shadow into sunlight, then a violet hue may then be observed. A white colouration in auroral forms is simply an amalgamation of the various colours blending together from a variety of chemical reactions taking place simutaneously. You can loosely think of this as the converse of taking white light and separating it into it's component wavelengths (i.e. colours).
Because of the angle between the magnetic and geographic poles, the auroral zone lies in high latitudes in north Norway where summer light prevents observation during that season and the polar auora can only be observed in winter. On the other hand, the storm aurora comes into lower geographic latitudes in Canada so that it can be observed there against a dark sky background in summertime. The daytime part of the polar aurora, which is diffuse and red in colour, can only be observed in the dark skies of the Arctic winter. For example, in Spitzbergen.
In the U.K., the probability of seeing storm aurora in winter increases the further north the observer travels. However, it is not possible to predict in advance when an aurora can be seen, so that planning an expediation in adavnce to observe and record auroral activity is impossible. This probability increase's when one takes into account the factor of the sunspot cycle [depending of course as to whether we are at solar minma or maxima]. Cloud cover is always a problem and some observing sites are much more affected than others. Observations suggest that on average, it is possible to obtain sky conditions suitable for the dectection of aurora on only 1 night in 5 but the effect of the local environment can reduce this probability even further.
| Location | London | Nottingham | Carlise | Aberdeen | Wick |
| Maximum Annual No. | 15 | 23 | 62 | 104 | 138 |
| Minimum Annual No. | 0 | 4 | 13 | 44 | 50 |
In the context of the above table, aurora may be only a glow with an arc and therefore neither spectacular nor readily detectable. Note that moonlight effectively prevents the detection of much auroral activity as do streetlights and the associated light pollution. It will be noted from the above brief statistics that in order to observe the aurora form the U.K. it is necessary to spend some time in a given locality before being sure that activity may be seen
"Where and when can I see aurora?" is a frequent question in enquirers letters. The short answer is to take a job in Wick or Kirkwall and wait. U.K. tourists spending fortnights at Reykjavik in September have been lucky. One observer who has spent weeks during February in northern Norway under the auroral oval, has seen precisely nothing due to cloud cover. Records show that here in the U.K. clouds can persist for up to 28 nights in succession. The precence or absence of cloud depends upon the weather patterns in north west Europe and the locations of the high and low pressure regions. From analysis of all contributing observers the best locations for clearest skies and frequency of auroral activity would appear to be north Dakota although other similar locations in Canada and the northern U.S. may well exist.
Magnetic midnight is defined as the time when the observer, the magnetic pole and the sun are in the same straight line and in the U.K, this is at around 22:00UT. Magnetic midnight is the most likely time of night to see aurora activity when the observer is then closest to the auroral oval, if active. Similarly, provided there is no full moon at the time, aurora is more likely to be seen at the equinoxes than at other time of the year.
The beginner need only confine themselves to noting location, the double date of the evening/morning of the observation concerned, clock time in Universal Time and a description of the aurora in writing with or without sketches. More experienced observers should try to observe each change in form and make make notes using the Auroral Reporting Code at intervals of 5 minutes.
Magnetic midnight takes place at around 22:00UT in the United Kingdom, so it is useful to scan the sky each night at around this time when the probabilty of auroral activity is at it's highest. Aurorae are more likely to be seen at the equinoxes, but for statistical purposes it is desirable to keep an all year round watch for activity. The frequency of the aurora tends to follow the sunspot cycle but peak activity may appear a year or so after sunspot maximum.
In order to measure the position of the auroral forms, an observer may make for themselves a simple theodolite, or may obtain the azimuthsof hoizon features from a map, or may convert from the declination and right acension of the stars in the background sky. Angles in the sky can be estimated by using the hand at arm's length as a measure.
This can be checked by counting hand's-breadths from horizon to zenith.
One can also calibrate measurements by using the angular distance between well know stellar groupings :
Each observer will have his/her own best measure - across the finger tips or across the knuckles - depending on the length of the arm and on how he/she choose's to hold one's hand. There is a tendancy for observers to over estimate the angles that a display subtends in the sky, hence, it is advisable that the observer is confident with his/her measurements i.e. practice!. A meteorological hand held cloud alidade can be used for height measurement, and these are simple to make at home.
In a large and active display, it is generally impractical to attempt a complete description of all the forms and types of activity observed; what can be useful is an indication of the time of greatest extent or greatest brightness. The intensity of auroral light is aften too low to stimulate the colour sensitive parts of the eye, and auroral forms may have the grey-white appearance of cloud lit by weak moonlight. But at higher intensities (or to a dark adapted eye] aurora can exhibit a variety of colours, mainly greens and deep reds. Look especially for red ray's and patches above or to the side of the main display and for red borders to the lower edges of rays, bands or arcs. Interference filters passing the auroral emssion colour green at a wavelenght of 5577 angstroms may be used to search for aurural light in cloudy, moonlight hazy or light polluted areas. However, such filters are expensive to buy.
Condition
| Q | Quiet, No movement |
| a | Active |
| a1 | Folding of bands |
| a2 | Rapid change of shape of lower form |
| a3 | Rapid horizontal movement of rays |
| a4 | Forms fade quickly to be rplaced with others |
| p1 | Pulsating, Rythmic change of form as a whole |
| p2 | Flaming, Variations moving upwards |
| p3 | Flickering, Rapid irregular variations |
| p4 | Streaming, Irregular horizontal variations in homogeneous form |
Qualifying Symbol
| M | Multiple, Several groups of forms |
| F | A part of only an auroral form |
| C | Rays converging |
Structure
| H | Homogeneous, Uniform in shape and intensity |
| S | Striated, Lines of brighter and darker light |
| R1 | Rayed, Short rays. |
| R2 | Rayed, Medium length rays. |
| R3 | Long rays |
Auroral Forms
| G | Glow, From horizon upwards |
| A | ARC, A uniformly curved arch of light |
| RA | Rayed ARC, ARC from which rays appear |
| R | RAY, A vertical shaft |
| B | Band, Twisted ARC |
| V | Veil, Indefinite |
| P | Patch, Isolated cloud of aurora |
| N | Undefined, Does not indentify with other forms |
Brightness
| 1 | Weak, Barely visible |
| 2 | Bright as moonlit cirrus cloud |
| 3 | Bright as moonlit cumulus cloud |
| 4 | Bright enough to cast shadows |
Colour
| a | Red, Only in upper part of form |
| b | Red, Lower border only |
| c | White, Green or Yellow |
| d | Red |
| e | Red and Green |
| f | Blue or Purple |
Description of Auroral Forms
| GLOW (G) | Most frequently seen mid-latitude aurora, the word "glow" is to be used only when the auroral light is observed on the horizon |
| ARC (A) | Aurora often takes the form of an ARC (A), extending east-westwards across the sky. There is an area of sky below the lower edge, which is usually more clearly defined than the upper edge. When an ARC has no vertical ray structure it is called a HOMOGENEOUS ARC (HA) |
| RAYED ARC (RA) | When an ARC shows vertical ray structure it is called a RAYED ARC (RA). This form usually exhibits moderate activity, that is, small movements and irregular brightness variations. |
| RAY (R) | A common form assumed by the auroral light is that of a RAY (R), which is like a searchlight beam. Usually nearly vertical, rays may occur singly or in bundles. |
| BAND (B) | Sometimes the auroral light forms a BAND (B) wihtout the regualr shape of an arc. If there is no ray structure, then it is called a HOMOGENEOUS BAND (HB) |
| RAYED BAND (RB) | When a band shows ray sturcture it is called a RAYED BAND (RB). If the rays are long, it may resemble a curtain or drapery waving in the sky. |
| SURFACES (S) | Sometimes there are patches of auroral light without distinct boundaries, in clear sky (so that it is not the effect of obscuring clouds) and well up form the horizon (so that it is not a GLOW). These forms are called surfaces. |
| CORONA (C) | When rays or other forms pass overhead, perspective causes them to converge to a point to form a crown or CORONA (C) |
| PULSATING (P) | Any of these above forms may disappear and re-appear rhythmically and periodically at the same place with a period of anything from 10 to 100 seconds. This kind of activityis called PULSATING (P). The synbols PS, PA, etc, are used. |
| FLAMING (F) | Another form of activity called FLAMING (F) occurs usually after a vigorous display of bright forms. It consists of waves of light moving rapidly upwards towards zenith, one after the other, lighting up existing forms as it passses over them. |
Use any SLR camera faster than f/2.8, set up on a rigid, stable tripod with a cable release for timed exposures. Load the camera with one of the following suitable films :
10 second exposures may be used on bight displays, but it is worthwhile to experiment with different exposure times. However, if exposures are above 30 seconds then the effects of star trailing will begin to occur. It is important that the observer record the date (double standard as explained earlier], time [UT], cmaera, aperture, exposure, film, observers latitude and longitude and the direction of view (azimuth etc].
Construct a simple magnetometer -as described in the BAA Journal Vol. 93, No.1, Dec 1982 page 17. Measure the differential movements of the magnet in hourly intervals. If large deviations are detected in the evening, then increase the frequency of your measurements i.e. every 15 minutes. Record the date and time of each reading. If rotation westwards is followed by a rapid movement eastwards, visual auroral activity may be detected. Local experience will soon teach the observer the differences between diurnal variation, storm conditions and the effects of local magnetic interference.
Point A3 or 4 element Yagi aerial northwards and listen to the 4 metre amateur band. Clean high pitched morse reflected from auroral ionisation will be heard as a low pitched rasp. Weak or wavery signals in 3.5-7 MHz band are indicative. Transmission will be heard over much longer distances than normal and stations beyond the radio horizon may be detected. Radio aurorae may be looked ofr in the afternoon but it's presence may not necessarily precede a visual aurora. Record the date, time, location of receiver, the stations detected, the waveband being worked and the interference to signals detected. For further details see Radio Society of Great Britain Handbook.
General
University Level
For more information on the Aurora Section, or if you wish to contribute an observation or observational data, then write enclosing a S.A.E (or appropriate international return mail) to :
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