British Astronomical Association
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British Astronomical Association
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Meteor Section |
The Meteor Section of the British Astronomical Association encourages amateurs to become involved in meteor astronomy through active observation, Section meetings, and contributions to the Section Newsletter and other publications of the Association.
Occasional reports are published in the Journal of the BAA. An account of the activity of the Section each year can be found in the Report of the Meteor Section, part of the Association's Annual Report.
Unfavourable lunar phasing has affected many of the major annual showers through the autumn of 2005, the Orionids, Leonids and Geminids each being notable casualties. A couple of reasonably favourable opportunities remain before meteor activity hits its annual low point during late January into February.
Active December 17-25 Radiant RA 14h 28m Dec +78o
A much-neglected but moderately active shower, the Ursids are produced by debris from Comet 8P/Tuttle. The radiant, near the ‘dipper’ or ‘Guardians of the Pole’ in Ursa Minor, is circumpolar for observers at the latitudes of the British Isles; at the time of maximum on December 21-22, it is highest during the early morning hours – figures below are for 53oN:
Local Time Altitude Local Time Altitude 18 42.8o 01 47.5o 19 41.6o 02 50.3o 20 41.0o 03 53.4o 21 41.1o 04 56.5o 22 41.9o 05 59.5o 23 43.2o 06 62.1o 00 45.1o
Moonlight will present some problems in the later parts of the night – the Moon reaches Last Quarter on December 23. Watches in late evening should, however, still be productive.
Ursid meteors are fairly slow (atmospheric entry velocity 33 km/s), and mostly quite faint. Observed rates are usually less than 10 meteors/hr, but occasional unexpected outbursts have occurred, as in 1946, 1982 and 1986.
Active January 1-6 Radiant RA 15h 28m Dec +50o
Of the major showers capable of producing strong activity, the Quadrantids present the best dependable opportunity for observers to enjoy high meteor rates until the closing months of 2006. The shower has a narrow, sharp peak during which corrected Zenithal Hourly Rate (allowing for haze and radiant elevation above the horizon) can be as high as 120 – corresponding to observed rates of one or two per minute. High activity is restricted to within about 8 hours either side of the peak; at other times, only a slow ‘trickle’ of one or two meteors/hr is evident.
In 2006, maximum is expected at Jan 3d 17h UT, early in the evening for observers in the British Isles. At this time, the shower radiant (in northern Bootes, down and to the left from the Plough’s ‘handle’ from the UK perspective) is sinking towards the northwest of the sky. Even with a relatively low, and declining, radiant elevation (see table for 53oN below), high rates could make the evening hours of Tuesday-Wednesday Jan 3-4 productive. A 4-day waxing crescent Moon shouldn’t interfere too badly, low in the western sky and setting around 20:30 local time.
Local Time Altitude Local Time Altitude 17 22.5o 00 21.8o 18 18.1o 01 27.2o 19 14.9o 02 33.3o 20 13.3o 03 41.8o 21 13.1o 04 49.0o 22 14.6o 05 56.9o 23 17.5o 06 66.3o
The Quadrantid radiant is, in fact, circumpolar from the latitudes of the British Isles, meaning that activity can be seen throughout the night. Lower culmination, due north, is reached around 21h local time, bit the radiant doesn’t really start to climb to any great elevation in the eastern sky until well after midnight, by which time rates on 2006 Jan 3-4 can be expected to be in decline.
Results in past years have shown significant particle-sorting by size with in the Quadrantid meteor stream. At the time when visual activity is highest, the majority of Quadrantids are faint (smaller material). Photographic-range meteors (magnitude 0 and brighter) become more abundant some hours after maximum. In 2006, UK-based observers will be in the ideal longitude zone on Earth to witness and record the ‘bright meteor’ phase of the Quadrantids.
Quadrantid meteors are fairly slow (atmospheric entry velocity 42 km/s), and the brighter shower members are sometimes strongly coloured (often blue or green). The stream’s dynamic orbital history – much perturbed by Jupiter’s gravity – has made identification of its parent body difficult. It has been suggested that Comet 96P/Machholz may be the source, while more recent studies have proposed that the Quadrantids may be debris from asteroid 2003EH1, a possible break-up product of Comet 1490Y1 following the latter’s close approach to Jupiter in 1650.
Poor January weather frequently limits, or completely prevents, Quadrantid observations, and the shower hasn’t been well covered for many years. Observers are therefore urged to make the best possible use of any clear skies during the shower’s activity period in 2006.
Observations of any of the above showers, made by the BAA Meteor Section’s standard methods - outlined elsewhere on these pages - will be welcomed by the Director.
Neil Bone
neil<-at->bone2.freeserve.co.uk
In pleasant contrast with the virtual washout a year previously, weather conditions for the core part of the Perseids in 2005 were reasonably favourable. Best skies were found in the southern UK, where some fortunate observers managed to put in productive meteor watches on seven consecutive nights from August 6-7 to 12-13 inclusive. The fine weather broke to cloud and rain on Aug 13-14, which at this writing is the only night for which the BAA Meteor Section lacks coverage during the most active parts of this year’s Perseid return. Clear skies were back for Aug 14-15 and 15-16, after which the waxing gibbous Moon, setting late in the night, became too intrusive to allow continued observations of the Perseids’ decline.
As of 2005 August 25, 30 sets of reports totalling 132h48m observing time had
been received from those listed below:
G Beadle, G Bone, N Bone, P Brierley, A Burns, A Drummond, P Dyson, A Farr, D
Gavine, M Green, A Heath, M Hurn, R Johnson, J Lancashire, T Lloyd Evans, H
McGee, T Markham, B Mizon, J Randall, I Ransom, I Ridpath, G Spalding, C Steele,
M Taylor, J Weightman, A White, V White, I Wood, Basingstoke AS, Worthing AS
A total of 1966 meteors (448 sporadics, 1300 Perseids, 58 others) has been reported so far.
Preliminary analysis has been undertaken to determine Zenithal Hourly Rates (ZHR) for the 2005 Perseids, making allowance for the angular elevation of the radiant above the horizon, and sky transparency. Results are summarised in the rates curve:
Perseid activity was already noticeable by Aug 6-7, with observed rates up to 5 meteors/hr corresponding to ZHR ca. 10-16. By Aug 10-11, a marked increase in activity was evident, ZHR climbing towards the mid-20s.
Peak was expected around 13h UT on August 12 - during daylight for UK-based observers. Activity was certainly climbing late on the Thursday-Friday of Aug 11-12, with ZHR 60-70 towards dawn. Immediately following the peak, rates on Aug 12-13 were again high - ZHR about 70 in the hours around midnight UT. Late on in the night, activity appears to have declined somewhat, ZHR dropping towards 40.
Fewer data are available for Aug 14-15, but it appears that by then ZHR was falling off towards the 20s, and lower still on Aug 15-16 as the usual rapid decline set in.
Overall, rates give the impression of a fairly 'normal' Perseid return. Some reports on the websites of the American ‘glossies’ suggest observer disappointment with the rates, but a measured analysis shows that these were comparable with most years in the 1980s, say, and with the well-observed 2002 return: perhaps some expectations were artificially high in recollection of the enhanced Perseid returns of the early 1990s around the perihelion of the parent comet (109P/Swift-Tuttle)?
Magnitude data for 336 sporadics and 939 Perseid meteors are summarised in the histogram below:
As usual, the Perseids showed an increased proportional abundance of bright events, and depletion at the fainter end of the magnitude range, relative to the sporadic background. Overall mean Perseid magnitude was +1.88 compared with +2.56 for sporadics in the same time interval - values, and a difference, typical of recent past years. The respective values on Aug 12-13 - the night of highest activity over the UK - were +1.77 and +2.61.
Persistent trains were left behind by 24.1% of Perseids, 4.8% of sporadics - again, pretty much in keeping with proportions seen in most years.
Alex Pratt (Leeds) and Len Entwisle (Elland) again ran video cameras in the
hope of recording two-station meteors; Richard Sargent (Chester) also
collaborated on this work. Early reports suggest numerous trails were captured
for later analysis. Low light video exposures were also carried out by Steven
Evans and Andrew Elliott. Several photographers were also active. James
Weightman is among those who captured Perseids on digital camera.
Reports continue to arrive in large numbers at the time of writing, and a full
formal analysis will be carried out in a few months' time once everyone has had
the chance to submit their observations. Any outstanding reports will, of
course, be welcomed by the Meteor Section. Many thanks to all observers for
their efforts and prompt submission of results.
Neil Bone
26th August 2005
Naked eye observation of meteors is one of the easiest and most pleasant form of work open to the amateur astronomer. Even a beginner can make useful observations, and it is a good way to learn the constellations. Meteor work is excellent for clubs and societies with little or no equipment; essentially only the human eye is needed.
The notes below assume that a single observer is on watch, though most of what is said is relevant to group observation. Organisation of a meteor watch by a group of observers is more complex, though potentially productive of much more useful data; a separate page outlines Group Visual Watches.
The first requirement for the observer is to find a good dark site. Rural
residents are favoured here. Urban lights, smog and haze have a major,
adverse, impact on meteor rates. Hence, even if you have to drive some miles
to get to a good site, it will be well worth the trouble to have darker
skies.
Equipment considerations are minimal. The major ones are:-
1. Norton's 2000.0 Star Atlas or similar.
2. Report sheets or similar.
3. Timepiece - accurate to better than 30 seconds. Please check beforehand using BBC time signals or the Speaking Clock. Remember that between March and October you must subtract one hour from the Civil Time (British Summer Time) to give Universal Time (UT), which is the standard employed in all astronomical observations.
4. Dim red torch - to enable you to note down data, but retain the dark adaptation of your eyes.
5. Several pens or pencils. These have a habit of breaking or getting mislaid in the dark, so have plenty of back-ups!
6. Cassette tape recorders are used by some observers to record data during a meteor watch. Dewing plus electronics can, however, spell disaster; tapes run out and other malfunctions all too often result in data loss. Used with care, however, they can be of considerable value; for example, in recording details of particularly interesting or spectacular fireballs, while they are still fresh in the mind.
7. Deck chair or similar, so that you can look at the sky at the best elevation of about 50 degrees in comfort.
8. Clothing. Bring plenty of this; even on a summer night it can get chilly, and it is better to have too much clothing than too little. One advantage of a house back-garden site is that one can retreat indoors to warm up if necessary. A hat reduces loss of body heat from the head.
9. Food and drink. Refreshments should be available to be taken during breaks. Alcoholic beverages should, of course, be avoided!
Observer requirements are rather more stringent:-
1. Patience. This is the prime requirement. The observer may face long intervals between meteors, or waiting for clouds to pass. Eagerly-awaited shower maxima often appear to turn out cloudy, and observations may have to wait for another year. Remember, however, that observations are required on all possible nights during a shower - so don't just restrict watches to maximum night,. One advantage of group watches is that the company helps to pass cloudy intervals.
2. Alertness. You must always be alert, otherwise the fainter meteors, which generally make the bulk of the bag, will be missed. If you are tired, or cold, or find your attention wandering, you should stop observing, at least for a while, since your results will not be reliable.
3. Honesty. All observers have different eyesight, and perception for meteors. An observer must not be disappointed to see fewer meteors than a colleague. Meteor work is not a competition, and conscious or unconscious 'doctoring' of observations is worse than useless, and indeed misleading.
Having covered the instrumental and personal requirements, we can get down to what is required from the observations. Before going outside to observe, find the radiant co-ordinates for the shower(s) active on the night in question , using the Meteor Diary in the BAA Handbook. It is important to note that the radiant position in the Handbook is for the night of peak activity only. In accordance with theory, radiants generally move among the stars at a rate of about 1 degree per day. So, for a night other than maximum, the radiant will have RA and Dec different from the Handbook values. The Meteor Diary lists the daily motion, where known, for major shower radiants. Multiply these figures by the number of days - positive or negative as the case may be - that you are away from the shower maximum. Add the results to the maximum night values of RA and Dec, and you have the radiant position for the night in question.
Plot this position in Norton's, and draw a circle of 8 degrees diameter centred on this position. The enclosed area is taken as the radiant for the night in question. Examine this area carefully indoors, until you are confident that you will recognise the area in the sky when you actually begin to observe.
Once outdoors, use the time that you spend getting dark adapted to record your name, address, and observing site (including latitude and longitude), and date on the report sheet. Note the sky conditions, mentioning whether any cloud, moonlight, fog or mist is present. Once you are fully dark-adapted, estimate the magnitude, to the nearest 0.25 mag, of the faintest star you can see in the area of sky being watched (not the zenith). Some observers prefer to estimate this limiting magnitude using the North Polar Sequence.
Now you are ready to begin the watch. Write down the start time of the watch in UT to the nearest minute. All times used in this type of work are required in Universal Time, which is equivalent to GMT. During the summer months, remember to subtract 1 hour to arrive at UT. Use 24-hour clock times - 10:15 pm GMT is 2215 UT, 11:32 BST is 2232 UT, and so on.
Of course, because astronomers work exclusively at night, the date changes at midnight, halfway through the observing period. To prevent confusion and ambiguity as to exactly which night the observations are carried out, one must record the Double-Date on the report form - for example, 30-31 October.
Some observers, once they get past midnight, use the 24-hour clock beyond the figure 24 so that, for example, 2 am becomes 2600 UT. This is quite acceptable. So long as your record of date and time is unambiguous, do what you find most convenient.
As the name implies, a meteor watch involves concentrating on the sky and noting details of any meteors seen. Solo observers should watch the sky 50 degrees above the horizon (about the same altitude as Polaris from the UK), and 30-40 degrees to one side of the shower radiant expected to be active on the night in question; most meteors should be seen here.
As each meteor appears, not whether it was a shower member or a random sporadic, estimate how bright it was, and give its time of appearance to the nearest minute in UT.
To ascertain whether a meteor belonged to a given shower, or was a sporadic, mentally project its path in the sky backwards. If the projected path intersects the 8-degree radiant circle, the meteor is a shower member. Otherwise it is a sporadic. Those with paths tangential to the radiant should be considered as possible shower members. If a stick, or piece of string is held up against the meteor path when the event is seen, this will give you time to collect your thoughts after the meteor has vanished. Estimation of the magnitudes of shower and sporadic meteors may be omitted by those observers wishing only to carry out counts. The others should estimate meteor magnitudes by comparison with nearby stars. It will be adequate to estimate to the nearest whole magnitude. Do not forget that there is a mag. 0 between -1 and +1. Estimation of meteor magnitude is largely subjective, since the meteor is rarely present long enough to enable very accurate visual photometry; it is a remembered impression that is compared with the stars. For bright meteors, errors in magnitude estimation are much larger, due to the lack of suitable comparison standards. Useful tips for bright meteor estimation: Full Moon is mag. -12.5; Venus is -4.4 at its brightest; Jupiter about -2.2. Large scatter in the magnitude estimates of fireballs can hardly be avoided. The list here offers some further suitable comparisons for fainter meteors:
Magnitude Object(s)
-4 Venus
-2 Jupiter
-1 Sirius
0 Capella, Rigel, Arcturus
+1 Regulus, Spica, Pollux
+2 Belt stars of Orion, Beta Aurigae, Gamma Geminorum,
Pointers of Plough, Polaris, Denebola, Alphard
+3 Delta Ursae Majoris, Gamma and Delta Leonis, Epsilon Geminorum
+4 Eta Persei, Delta Aurigae, Rho Leonis
+5 Faintest meteors generally visible to naked eye
Note the time of appearance of the meteor, having made due allowance for
the time spent thinking about magnitude and type, and writing these down,
perhaps 15-30 seconds.
Then, and only then, you may make any notes about the meteor itself. For example, did it explode? Did it have an intense colour? Did it have a long-duration persistent train?
As this is the first time we have mentioned meteor trains, a few words about them would not go amiss. Many observers, especially beginners, are confused by the difference between meteor trails and persistent trains. A night-time meteor train appears as a faint nebulous streak of light left behind, along the track of a meteor, but AFTER the meteor itself has extinguished. Do not mistake it for the actual moving streak of a fast meteor - this is the trail. Momentary meteor trains are generally likened in appearance to the vapour wake of a jet aircraft, and are only left by about a quarter of all meteors. Meteor trains lasting more than a few seconds are quite rare. Statistically, one must observe about 600 meteors to observe a train of 10 seconds' duration or more!
Each meteor seen during the watch should be treated similarly; practice makes perfect, and you should soon be able to get down the data quickly and efficiently. Abbreviations such as "S" for sporadic, or "P" for Perseid, and writing the minutes instead of minutes and hour, will help you to cope with the sudden rushes of meteors that sometimes occur. As long as you get all the data down, and you can understand your symbols at a later date, you can use any symbols you like. Many experienced observers, to reduce "dead time" spent looking away from the sky, note meteor details in such a shorthand, for later, neat transcription to the Section's report forms.
At the end of the watch, note the time to the nearest minute. Then you can stop, or have a break and start another watch later. Ideally, watches should last for an hour, or multiples of an hour, at a time. Monitor the sky conditions during each watch, as these may change.
Given here is an example of an actual watch, logged on a BAA Meteor Section Visual Report Form, and carried out by the Director during the Leonids of 1995.
Reporting: Please submit your observations to the BAA Meteor Section as soon as possible after you have made them, and at any rate within one month at the most. Observations may be sent to your local Regional Co-ordinator, or to the Director:-
Neil Bone, 'The Harepath',
Mile End Lane, Apuldram, Chichester, West Sussex, PO20 7DZ. Tel. (01243)
782679. e-mail bafb4@central.susx.ac.uk
who will be pleased to answer any queries regarding further aspects of
visual meteor work.
The Section continues to regularly receive reports of bright meteor events, which are kept on file. By established definition, a fireball is technically any meteor brighter than the planet Venus - in other words, an event of magnitude -5 or brighter. Reports of fireballs are frequently made during the major annual showers (the Perseids and Geminids are rich sources, as have been the Leonids during their recent high-activity years). Of potentially yet-greater interest are the isolated fireballs which may result from the arrival of sizeable chunks of interplanetary debris from the asteroid belt, knocked into Earth-crossing orbits by collisions in the astronomically-recent past (perhaps a few tens of thousands of years ago). The hope is always that analysis of eyewitness accounts of a fireballs will lead to recovery of any resultant surviving meteorites on the ground: the harsh reality of our island location is that most end up over the sea!
A majority of the sighting reports we receive come from single witnesses, which is unfortunate! Occasionally, however, major fireballs are seen by large numbers of people over a wider geographical area, allowing at least an approximate ground track to be established.
Page last updated:
16/12/2005
