12. kolovoza - Ne propustite pravi meteorski vatromet, sastavljen od mnoštva perzeida, poznat još kao »suze sv. Lovre«.
»Naime, Zemlja u svojoj uobičajenoj orbiti jednom godišnje ulazi u 'prstene', sastavljene od meteora (leonida, perzeida i geminida) koji putuju oko Sunca. Među njima su i perzeidi, najčešće komadići prašine ili leda od kojih je najveći veličine zrna graška. Oni putuju velikom brzinom od 60 kilometara u sekundi i za sobom ostavljaju usijani trag dug po desetak kilometara te širok nekoliko stotina metara. To ujedno znači da ćemo u sat vremena golim okom moći vidjeti između 50 i 100 perzeida«.
Preporuča se maknuti iz grada i promatrati ih sa sela ili nekog nenaseljenog područja, gdje predstavljaju pravi kozmički spektakl. Naime, ulična rasvjeta ometa promatranje meteora zato što svijetli u nebo i tako onemogućava promatranje. Selo je najidealnije mjesto gdje se pod vedrim nebom najbolje vidi »potok meteora«, koji bi svatko tko nije trebao vidjeti, a na »Dan kada padaju zvijezde«, nije naodmet zaželjeti i koju želju.
Iako se čini da su blizu, perzeidi od Zemlje prolaze na visini od 100 kilometara, a postaju vidljivi ulaskom u atmosferu kad za sobom ostavljaju svijetleći trag. Perzeidi inače dolaze s kometa »Swift Tuttle«, te nastaju raspadom njegovih vanjskih slojeva. Taj komet u Sunčevu orbitu ulazi svakih 135 godina i, prema sadašnjim saznanjima, ne postoji opasnost susreta sa Zemljom. Ako bi do njega došlo, bio bi katastrofičan, jer komet ima promjer od gotovo 10 kilometara.
Prvi perzeidi, prema nekim kineskim zapisima, viđeni su još 36. godine poslije Krista, a u kineskim, japanskim i koreanskim kanalima brojne su zabilješke o njihovom viđenju tijekom srednjeg vijeka, nakon čega je do 19. stoljeća stanka. Tada se, 1835. godine, zasluga uočavanja meteora pripisala izvjesnome Queteletu iz Bruxellesa, koji je tvrdio kako je vidio potok meteora iz zviježđa Perseus. Nakon toga, tijekom 19. stoljeća, uslijedio je niz proučavanja »perzeida«, a broj njihova prolaska kroz sat vremena, prema kraju stoljeća, povećao se sa šezdesetak na više od dvije stotine! Nakon toga broj se stabilizirao, spustio na uobičajenih šezdesetak, da bi se početkom dvadesetog stoljeća spustio na samo četiri perzeida u sat vremena i 1920. godine ponovno naglo skočio na 200. Do kraja 20. stoljeća, broj perzeida, najčešće se »vrtio« između 50 i 100, a njihov broj bio je i najčešće mjerena stopa.
»Radi se o potoku meteora, a ne o roju, niti o kiši« čime postaje i jasnije srednjovjekovno pučko vjerovanje prema kojem »nebo plače za svetim Lovrom«. Za istaknuti je kako su perzeidi obično mnogo svjetliji prije nego dosegnu svoj maksimum.
Perzeidi, za Zemlju potpuno bezopasni, mogu biti opasni jedino za satelite u Zemljinoj orbiti. »Tako je 1993. godine nastradao i milijardu njemačkih maraka vrijedan satelit 'Olympus', koji je, tako oštećen, vraćen na Zemlju«.
Zadnja promjena: obyzouth; 10.08.2008. 21:36; ukupno mijenjano 1 put.
_________________ I do it because I can. I can because I want to. I want to because...Anonymous said I couldn't!
U biti već zadnjih noći sam primjetila pojačanu aktivnost, ulovila sam i par pravih bolida , najviše će se vidjeti u noći s 11 na 12 i s 12 na 13 i to pred jutro, negdje oko 3-4 sata. Ekipicu i na promatranje
_________________ I do it because I can. I can because I want to. I want to because...Anonymous said I couldn't!
One of the best times to try and photograph meteors is during the Perseid meteor shower. All you need is a camera capable of exposures lasting one minute or longer. Simply aim the camera high enough to clear the horizon and set the focus to infinity. Don't aim the camera straight up as this is the worst direction for meteor activity. The layer of air directly above you is the thinnest therefore less activity will be seen there compared to the denser portions of the atmosphere located closer to the horizon. Also try to center the camera 30-60 degrees from the radiant so that the meteors are long enough to be easily seen on your photograph. Meteors appearing near the radiant will appear shorter as they are traveling in a direction toward you. It is also advisable to use the fastest film/ ISO setting possible to increase the sensitivity of you camera. Meteors will appear as straight streaks overlapping the curved trails created by the stars moving through the field of view. The length of the star trails will depend on the length of your exposure and the direction you point the camera. Pointing your camera northward will decrease the length of the star trails. Some photographers eliminate the stars trailing by mounting their cameras on motor driven mounts. With this setup the stars remain as pinpoints while meteors are obvious streaks.
It is also enjoyable and scientifically useful to record the meteor activity you see. Experts in meteor astronomy can reduce your data and compare it to others all over the world if you use certain standards in your reporting. First and foremost is to provide the accurate time of your observing session. It is helpful to time each meteor but not absolutely necessary as long as the start and finish times are provided. The observing conditions are very important to properly record, especially if your field of view is obscured by clouds or trees. These obscurations should be recorded to the nearest ten percent. Once per session is fine for trees but at least every 15 minutes for changing conditions such as cloudiness. The limiting magnitude of the sky in your field of view should also be recorded at least once an hour. The easiest way to do this is to count the number of stars visible in pre-selected areas of the sky. These star count areas and the resulting equivalent limiting magnitudes are available online from the IMO web site at: http://www.imo.net/visual/major/observation/lm
Please note this is my first time ever I actually attempted to photograph the sky, and actually stayed up for few hours. Next time I hope that I can get better grip handling the camera, settings and choice of lens, so I can spend more time aiming. Aiming is difficult because you cannot predict where it will show up - only roughly. Since the wide angle lens was not giving me what I wanted, I had to move on with my 28-80mm lens. This did not give me clear image but stars were more apparent. I kept my shutter opening variable, sometimes for 30 sec, and sometimes for 10 sec, however, I clicked and clicked. Well I think I captured two meteors as you can see on the two photos below. Not that spectacular but hey better than nothing. I believe these are meteors because the first one showed some fading. The second one is more a straight line, but this is because the shutter opening expired, so did not catch the rest.
ISSUED BY: The International Meteor Organization (IMO), August, 1994.
Below is the Frequently Asked Questions (FAQ) list for the Perseid
meteor shower as prepared by the International Meteor Organization
(IMO). Contributors include Peter Brown, Malcolm Currie, Marc Gyssens,
Juergen Rendtel, and Rainer Arlt.
(email addresses at bottom).
****************************************************************************
C O N T E N T S
1. What is the best time to see the Perseids in 1994, and will moonlight
interfere?
2. How many meteors will I be able to see near the maximum?
3. How do I recognize a Perseid?
4. Where is the best place to observe the Perseids?
5. In which direction should I look to see the Perseids?
6. Why have the Perseids been so strong over the last few years?
7. How big is the meteoroid which causes a typical Perseid?
8. Some of the meteors I see during the night of maximum don't
seem to be coming from Perseus - are there other meteor showers
visible at this time of the year?
9. I want to photograph the shower. How can I best go about
accomplishing this?
10. I have a video camera and would be interested in trying to get
useful meteor recordings from it for use in analyses; how can I
do this?
11. Are binoculars useful for observing the Perseids?
12. Are there any good books I can get to tell me more about meteors and
the Perseids?
13. I plan to watch the Perseids visually. How can I contribute to the
scientific understanding of the shower and what methods should I
employ?
14. I understand that the Perseid meteors can be heard using
Radio Equipment. What exactly is involved in doing this and
how could these data be gathered in such a manner as to be
useful?
Appendix A: The 1994 IMO Shower Calender.
Appendix B: The IMO standard visual count reporting form.
Appendix C: Useful addresses.
***************************************************************************
1. What is the best time to see the Perseids in 1994, and will moonlight
interfere?
A: The best night for the Perseids from North America will be Thursday
evening, August 11 and the morning of Friday, August 12. The time of
the true peak in meteor activity is somewhat uncertain, but it should
be between 7-11 UT (?-? EDT) on August 12. This peak may only last
for an hour or two. For other locations, there is a second smaller
peak (the "regular" peak) which will occur at about 21 UT on August 12
and hence favor European observers. If from your location both of
these times occur during daylight or either corresponds to early
evening, then from that location the most meteors will likely be
visible in the early morning hours on either the morning of August 11
or 12. There is considerable activity from the Perseids for several
days on either side of these dates and any early morning hour from
Aug. 7 to Aug. 14 should show many Perseids.
The moon will not interfere with Perseid observations until August 14.
On the evenings of August 11 and 12, it will be a crescent low in the
south-west, and will set around the time skies darken sufficiently
for meteor watching to commence.
2. How many meteors will I be able to see near the maximum?
A: There is no one answer for this question. The number of Perseid
meteors you can see depends critically on the darkness of your sky,
the amount of sky visible and the total length of time you look. For
every stellar magnitude lost in sky brightness (the limiting stellar
magnitude of your sky (LM)), the fraction of meteors decreases by 2 to
3 times. So an urban area where the faintest visible star is only 4
should show only about a quarter to a ninth of the number of meteors
visible from a location with a limiting magnitude of 6. The angle
elevation of the radiant also plays a critical factor as does the
intrinsic flux (number per unit time) of Perseids encountering the
atmosphere. There are varying opinions on the expected flux for the
first peak, so any predictions, especially of storm activity, should
be taken with a pinch of salt. If you observe from a mid-latitude
site which is in the country and your LM is better than 6 on the
morning of the maximum between 7-11 UT (August 12) you may be able to
see 150-200 or more Perseids/hr. Under similar conditions for the
"regular" peak, you ought to see around 60 Perseids/hr.
3. How do I recognise a Perseid?
A: The Perseids are so called because they appear to come from the
constellation Perseus at the time of their maximum; specifically a
point near the double cluster in Perseus. This point, called the
radiant, is actually about 5 degrees across because the cometary
debris (meteoroids) comprising the Perseid stream follow slightly
different orbits around the sun. There are additional identification
aids. A Perseid meteor seen away from the radiant has a high angular
speed compared with other meteors. Those seen in Perseus itself will
have short paths, becoming longest 90 degrees from the radiant. So if
you see a meteor in Perseus traverse say 20 degrees, it is not a
Perseid. Most bright Perseids (mag. +1 and brighter) leave faint
spindle-shaped glows along their paths called trains. These normally
last for less than a second, but ones resulting from fireballs can
persist for many seconds or even minutes. To most observers bright
Perseids appear yellowish in color.
4. Where is the best place to observe the Perseids?
A: For the reasons given above, meteors are best seen from a dark,
haze-free site that has an unobstructed horizon. We recommend that
those in North America select a location that best matches these
characteristics and has a high probability of being clear, rather than
travel long distances to try to second-guess when the first maximum
will occur. Virtually any longitude in North America could be optimum.
While the Perseids are observable from latitudes north of ??, the best
lie in the range 40 to 55 degrees north. Further north twilight
interferes; further south the radiant is not circumpolar and does not
rise until later, so gives less of a window to see any outburst.
5. In which direction should I look to see the Perseids?
A: Perseids will be visible in any part off the sky. The best
direction is strangely not towards Perseus. The direction to look is
about 40 degrees from the radiant and at an elevation of about 50
degrees. For the Perseids this corresponds to north and south-east.
6. Why have the Perseids been so strong over the last few years?
A: The peak activity of the Perseids has been larger than normal
because the parent comet of the stream, P/Swift-Tuttle passed through
the inner solar system in late 1992. Along with the comet came a
large number of meteoroids ejected at the last passage of
P/Swift-Tuttle in 1862 and these meteoroids are what the Earth is
currently encountering some ~12 hours before the normal peak of
activity. The "regular" maximum is much older and results from
material ejected by P/Swift-Tuttle over the last few hundred to few
thousand years. Records of the annual encounter of this portion of
the stream with the Earth go back over hundreds of years. It is the
young age of the new material which results in the short-lived
heightened activity, since the meteoroids have not had time to spread
out. The dispersion is caused by the different ejection velocities
from the comet and various non-gravitational forces acting on the
meteoroids.
7. How big is the meteoroid which causes a typical Perseid meteor?
A: For a meteor from the Perseids to be as bright as the brightest stars
(about -1 magnitude) the meteoroid must be about 40-50 mg in mass which
corresponds to a particle about 5 mm across (depending on what value for
density you wish to adopt). The faintest Perseids visible to the unaided
eye (about magnitude +5) are about 0.1 mg in mass.
8. Some of the meteors I see during the night of maximum don't seem to
come from Perseus - are there other meteor showers visible at this time
of the year?
A: The answer to this question is at the end of this FAQ where the
IMO's 1994 Meteor Shower Calender is posted. You will see that there
are many smaller meteor showers visible at this time of the year, so
not every meteor you see need be a Perseid. In addition there are
meteors that do not appear from known radiants. Under dark conditions
you could expect 8 to 15 of these sporadic meteors per hour. Their
number increase during the night about 50% from dusk to dawn during
the Perseids. On average they are fainter than the Perseids.
9. I want to photograph the Perseids. How can I best go about accomplishing
this?
(For those who just want to capture meteors on film for fun):
A: The art of meteor photography requires only a few items - a non-battery
operated camera with an optional shutter speed allowing long time exposures
and a tripod are the bare essentials. The film speed will depend on
your location - generally, modestly light polluted sites won't support
film speeds much above 400 unless the exposure is quite short. The actual
combination of exposure time, lens and film will depend on when you
observe and how light the background is. A dark site, a 50mm lens with
400 TRI-X and a 20 minute shot can produce excellent results.
(For those who want to take photos that can be used for scientific analysis):
A: There are very few occasions when the number of visible meteors
exceeds a level of about 100 per hour. Visual observers cannot accurately
record such events. As well, radio techniques may have problems with recording
this phenomenon due to saturation effects caused by the
superposition of signals from many meteor trails simultaneously.
Photographic and video observations are appropriate techniques under these
circumstances.
For the investigation of the meteor stream involved in such events, it
is very important that reliable magnitude data are obtained as well as
precise numbers of meteors per time unit. Because of the factors
involved in the ability of a lens-film combination to photograph
meteors of different angular velocity and brightness, there are
several, mainly geometrical reasons, which make this task more
difficult:
1. shower meteors move faster the closer one gets to 90 degrees
distance from the radiant;
2. shower meteors move faster near the zenith than near
the horizon; and
3. the film will record fainter meteors of low angular
velocity, or only bright meteors of high angular velocity.
Of course, there is no possible camera field which is not
affected by these factors. But we may minimize their influence.
The camera should be pointed 180 degrees away from the radiant in
azimuth. If a wide angle lens is used, the lower limit of the
field should be 10-20 degrees above horizon. For a standard lens
of f=50mm the elevation of the optimum field center depends on
the elevation of the radiant h rad. The most suitable
elevation of the field center h fc is given in Table 1.
\smallnewpar
At a mid-northern latitude 45 degrees the respective data are
listed in Table 2. For most of the night you may direct your camera
(with a standard lens) to the southwestern sky centered at about
60 degree elevation.
Table 1: Elevations of the field center (h fc)
depending on the radiant elevation (h rad) for the Perseids.
All angles are in degrees.
Radiant Elevation Field Centre Elevation
0 90
20 80
40 70
60 60
90 45
Table 2: Recommended camera fields for observers at 45 degrees
North latitude during the Perseid maximum. The azimuth is counted from
0 degrees at the true North.
It cannot be predicted in advance which exposure time will be most suitable.
If the activity exceeds the ability of visual
counting, perhaps a 10 minute exposure is appropriate. For
further increases in activity, ~2 minutes may be long enough.
For each of the photographs, the following data are required
in order that a scientific analysis can be made:
1. date
2. the exact beginning and end of the exposure +-1 s if possible; use UT);
3. the approximate field center in RA and Dec
4. site location and its geographic coordinates
5. focal length and speed of the lens
6. film type (sensitivity, format);
7. observer name and address
If you are lucky to record very high rates on photographic images,
please send copies (on paper or film) of the negatives to
the address at the end of this FAQ for further
analyses. Please, do not only send "the best of your images",
but also those obtained just before and/or after the highest rate.
10. I have a video camera and would be interested in trying to get
useful meteor recordings from it for use in analyses; how can I
do this?
If you have access to a video camera, you are encouraged to use it
for meteor work as well. Although normal color camcorders are
limited to about magnitude +2, the precise timing and frame-by-frame
analyses possible with video equipment compensates for
sensitivity limitations. Better sensitivities can be
obtained with special high sensitivity monochrome video cameras,
or with image intensified video cameras.
Use the largest aperture possible with your video camera lens. If
it is a zoom lens, you will want to select a fairly wide angle.
Once you have selected a zoom setting, do not change it
during the course of the observations. Set the focus to
manual at infinity, as some types of automatic focus mechanisms
will not operate properly when aimed at an almost black sky. For
our purposes, you will not want to use the electronic shutter
available on CCD video cameras since the sensitivity will be
further impaired.
Turn the time display to on and set it to the finest time
increment possible. Synchronize your clock time to a standard
time signal. If no video time signal is possible with your
camera, briefly blank the picture (by covering the lens) at
several recorded times. Recording a short wave radio time signal
on the audio track of the video recording offers another timing
possibility. Use high quality video tape, and in most cases
it is preferable to use the highest recording tape speed possible
(e.g., SP in VHS, Beta I, or Beta II).
Select an observing direction in the same way suggested for
photographic work, but adjust it as necessary to make sure that a
minimum of three stars are visible in your field of view.
It will assist with photometric corrections if, at the beginning or
ending of your observing period, you record several minutes of stars
in the sky with the same camera settings but with the camera skewed at
angular rates roughly corresponding to that of the expected
shower. Note the identifications of the stars used in the test.
Immediately after the observations, make a copy of the video tape.
It is acceptable (perhaps even preferable) to make this copy
on a slow tape speed (e.g. SLP in VHS or Beta~II), since
frame-by-frame advance is better on most machines with slow tape speeds.
In making the copy of your tape use the video in and video out connectors,
rather than the RF modulated signal. Be sure to use shielded cables intended
for video work in making the copy.
Carefully review the tape at least once (preferably twice) to
make a listing of all meteor occurrences. This will make it easy
for others to complete the analysis of your observations. For
each meteor, note the following:
1.time (UT) to the nearest second
2.position of meteor on the screen
3.apparent direction of motion
4.apparent angular speed (approximate)
5. approximate apparent luminosity, in magnitudes
Please send a copy of the tape to one of the addresses listed at the
end of this FAQ if you wish the data to be used in an analysis of the
Perseid shower.
11. Are binoculars useful for observing the Perseids?
A: Using a binocular you can watch persistent trains decay under the
influence of winds in the upper atmosphere. You may be lucky and view
a bright meteor as well. This is a thrill not to be forgotten.
Some experienced meteor observers also use binoculars and small
telescopes to study Perseids whose brightness is near or fainter than
can be seen with the naked eye. They plot these telescopic meteors on
special charts centred about 10 to 15 degrees from the radiant, and
analysis of these observations can reveal multiple components in the
Perseid radiant. Such observations also tell us the relative numbers
of different-sized particles in the stream. Unfortunately, since the
Perseids are deficient in faint meteors, a telescopic observer with
suitable instrumentation might only see a few Perseids per hour at
best.
12. Are there are any good books I can get to tell me more about meteors
and the Perseids?
A: There are several books which may be avaliable at your library
or through a book store which deal with meteors at many levels. For
beginning observers, the "Handbook for Visual Meteor Observations",
by Paul Roggemans (available from Sky Publishing for $19.95 US) details
the method used for visual meteor observing and also provides some
background into the subject. An additional reference providing more
background information, but with less emphasis on the observing
methods is Neil Bone's "Meteors" also available from Sky Publishing.
More advanced books on meteors include, "Meteor Science and Engineering",
by D.W.R. McKinley (1961, McGraw-Hill) and V.A. Bronshten's "Physics
of Meteoric Phenomena" (1983, Reidel).
13. I plan to watch the Perseids visually. How can I contribute to the
scientific understanding of the shower and what methods should I
employ?
A: An impressive number of observers monitored the maximum of the
Perseid meteor shower in 1993. It was no doubt the best observed
major shower maximum ever registered.
Theoretical predictions promise high activity for 1994 as well.
Peak rates should be comparable to 1993. We expect the total of
Perseids meteors seen in 1993 and reported to IMO to total
around 80 000. However, magnitude estimates were made for
only 50 000 of the meteors, although magnitudes are essential
data of a meteor.
The time of the primary peak probably coincides with the dark hours of
American longitudes on August 11-12. Observers should be prepared
for very high activity lasting for a few hours. There is little
reliability on rate predictions, but peak activity might be
at least as high as in 1993. The traditional
maximum occurs roughly half a day later, during the night August 12-13
for European observers. Watches on the night of August 11-12 will
probably show increasing activity towards the young peak, but they
will not show extra-ordinary rates in Europe. Do not forget that
an August 12-13 observation will impress European observers with
the high activity of the traditional maximum, which is still of
interest.
As meteors will appear very frequently, do not record a variety of
data to each meteor. The essential information of a meteor is the
shower association (shower/non-shower) and its magnitude. Do not
record the time of each individual meteor for counting purposes. Since there will be too
little time to reliably make minor showers associations during the
event, just count all non-Perseids as sporadics.
The meteors will be so numerous that magnitude distributions
will be smooth, even if you estimate whole magnitudes only. On the other hand, do
not make the opposite error by accumulating meteors of certain
magnitudes only. Try not to lose your sensitivity for differences in
brightness. With high activity, we have the unique opportunity to
investigate short-term fluctuations of the meteor stream: 15-20
meteors are a reliable statistical sample. These small numbers of
meteors will appear in a few minutes during the maximum night. Note
that you should not forget to record enough time stamps between the
meteors. Moreover, it is not essential that intervals are chosen at certain
"rounded" times, such as 0100-0130.
Feel free to use your relatively
regular time stamps to divide the observation into intervals. These
times may be, e.g., 0200, 0211, 0220, etc.
If you intend to use a tape recorder, just say the whole magnitudes to the
tape and mention the shower only if it was other than the Perseids
(so say, e.g., four, zero, one, sporadic two, three, minus two).
During high activity (observed rates above 100 per hour), observe the
following guidelines:
1. distinguish shower/non-shower only
2. estimate whole magnitudes
3. record time stamps at least every 15 minutes or, even better, every
10 minutes.
During the maximum of the
Perseids, there will be plenty of meteors. Expecting 10 times more
meteors than usual you can also define periods being ten times
shorter than in nights of normal activity. If the apparent activity
exceeds 50 meteors per hour, half-hour periods are the upper limit.
Breakdowns into quarter-hour periods are welcome unless they contain
less than 10 meteors. On the other hand, periods can be as short
as 5 minutes for an activity around or exceeding 200 meteors per
hour. Please report both Perseid and non-Perseid numbers for each
interval although there might be very few non-Perseids in a 5-minute
period.
Please report several Perseid magnitude distributions for the maximum
nights. A typical magnitude distribution should contain about
40-60 meteors. Hence, the periods will be half an hour or one
hour long. For convenience in the analysis, use the same time stamps
you used for the breakdown of the reported meteor numbers. You
should always remember that periods which are too short can easily
be combined into reasonable ones, whereas too long intervals cause a loss of
information. To ensure that the best is made out of your observation,
enclose a complete meteor list to your report. You will probably
have to write down the list once when you listen to your tape
anyway, so just make a copy of it and send it to the contact
addresses at the end of this FAQ.
To summarize, observe the following guidelines
when preparing your Perseid report:
1. When the activity is about 50 meteors per hour, report Perseid and non-Perseid
numbers for 15-minute periods. Give magnitude distributions per period of about 1 hour.
2. When the activity is about 100 meteors per hour, report Perseid and non-Perseid
numbers for 10-minute periods. Give magnitude distributions per period of about half an hour.
3. When the activity is about 200 meteors per hour or higher, report Perseid and
non-Perseid numbers for 5-minute periods. Give magnitude distributions per period of about 15 minutes.
4. Enclose a meteor list with the time stamps of the night.
To help make these observations, an IMO standard visual report form is
included at the end of this FAQ.
14. I understand that the Perseid meteors can be heard using
Radio Equipment. What exactly is involved in doing this and
how could these data be gathered in such a manner as to be
useful?
A: When a meteor enters the upper-atmosphere it leaves a trail
of electrons and positive ions in its wake. This column of electrons
can effectively scatter very high frequency radio waves.
The process of observing meteor trails with radio is
essentially a specular one. This is analogous to the case of
reflection from a mirror in simple geometrical optics - the
angle of incidence is equal to the angle of reflection. In the
application of this general principle to radio, however, the
visible light is replaced by a radio wave with a wavelength of
order several meters and the mirror is the dense column of
electrons produced when meteoric and atmospheric neutral
atoms experience mutual collisions. The electron volume density is
many orders of magnitude higher in the meteor trail than in the
surrounding ionosphere and so supports reflection of much
higher radio frequency (RF) waves (the atmosphere is a "natural"
radio reflector for RFs below about 3 MHz).
The physical interaction of the radio waves with the meteor
trail can be one of two types. If there are enough electrons to
scatter in such a way that mutual interactions between nearby
electrons is important, the radio wave cannot penetrate the full
column of electrons and the column acts as though it were a long
metallic conductor. Below this limit, the electrons act as
individual scatters and are not affected by surrounding electrons
to a great degree. These two broad categories of meteor trails are
called overdense and underdense, respectively. They are
delineated by the number of electrons produced per unit length of
trail; the electron line-density. Overdense trails have
line-densities in excess of roughly 10^14 electrons/m.
In amateur forward-scatter observations, the transmitter is
located many hundreds or thousands of km's from the receiver. The
transmitter is generally an FM radio station, an aircraft
beacon or a TV signal. The receiver is the "business" end of this
arrangement where the amateur meteor observer detects radio waves
scattered from the distant meteor trails. If the electrons in a
meteor trail reflect effectively radio waves for only a short
period of time, the trail is well approximated as a long, straight
column of electrons. In this case (which is usually applicable to
underdense trails), the geometry between the transmitter and
receiver has to be such that the radio wave can reflect off the
straight trail and reach the receiver. Such a geometry is only
satisfied for a few of the many small meteor trails and hence some
fraction of the total number of meteors will be detected. This
geometry changes with the altitude of the radiant relative to
the direction connecting the receiver-transmitter. The number of
meteors you will detect further depends on the mean length of the
meteor trails involved (which relates to the population or mass index),
as longer trails offer greater probabilities of scattering from any one
location.
On top of these effects, the wavelength you use, the height of the
maximum ablation for the meteors, the power and gain of the transmitter,
and the gain of the receiver will all affect the detection efficiency
of underdense trails.
We defer detailed technical descriptions of the antenna-receiver
systems, but note that a simple YAGI antenna and an FM radio
with the AGC disabled should yield meteor reflections. The Amateur
Radio Relay League (ARRL) Handbook is an excellent reference for
those interested in building YAGI antennae and/or details of
receiver systems in the HF.
To make meaningful quantitative interpretations of the flux of
underdense meteors from forward scatter observations, all these
effects (and more!) must be taken into account. In practical
applications, this further complicated as typical FM radio
frequencies have overlap from many stations so that the amateur
operating the receiver may really be detecting signals from many
transmitters all of which are indistinguishable as far as the total
echo rate is concerned. To make matters even worse, the small
meteors that produce underdense trails are much more prolific in
the sporadic background than in showers; even the Perseids at
outburst produce a fraction of the total number of underdense
trails.
Radio forward-scatter observations by amateur ham radio operators
and others have been valuable contributors in the past few years to
determining the time and peak strengths of the new Perseid peak.
Though the geometry involved can make interpretation more difficult, some
basic measurements with a forward-scatter set up can provide
useful data for analyzers trying to integrate information
from the many observational methods to develop an overall picture
of stream activity.
Observational procedure:
For many radio systems, the beginning of the overdense trail
regime is near visual magnitude +5. As such, most overdense trails
recorded by radio equipment should overlap quite well with visual
observations during the Perseids. Furthermore, many overdense
trails last long enough to distort in the upper atmosphere due to
wind shear. In such cases, the trail loses much of its aspect
sensitivity and multiple scattering centers may develop along the
trail. Particularly for overdense trails corresponding to brighter
meteors, some radio reflection should be registered by your
receiver. Since aspect sensitivity is lost in these cases, the fact
that multiple radio transmitters are present makes no difference.
By counting the number of overdense trails as a function of time,
you should be able to gauge the increase in Perseid activity quite
accurately. Sporadic meteor rates will be completely overwhelmed
at overdense echo durations by the increased flux of Perseids. The
overdense radio echo is typified by a quick rise to maximum
amplitude and then a near steady signal for a short time before the
amplitude decays exponentially. One strong disadvantage in this
case is when activity becomes very high, many echoes run together
so that near continuous reception of the FM signal occurs. It is
valuable to note both the number of overdense-type echoes you
record as a function of time and also the time intervals where
reflection is almost continuous due to the large flux of Perseids.
Another approach to radio observations of the Perseids is to
maintain a consistent setup for several nights on either side of
the maximum and record the number of echoes received. While
ambiguities exist in this technique, it does give a rough relative
indication of the increase in meteor rates near the time of
maximum. Included in the word "consistent" is the direction of the
antenna, the receiving antenna distance above the ground, the
frequency used and the same observing times each day or night.
The final results of your radio observation can be reported to
the email addresses given at the end of this FAQ.
*******************************************************************
Appendix A: The 1995 IMO Shower Calender.
compiled by Alastair McBeath
based on contributions from Rainer Arlt, Juergen Rendtel and Paul Roggemans
prepared for Usenet, Astronet and Compuserve by Andre Knoefel
(special thanks to Loreena McKennitt for her nice music during the
preparation...)
Introduction
============
Welcome to the 1995 International Meteor Organization (IMO) Meteor Calendar.
Inside we present notes on some of the more interesting, or favorably-placed
meteor showers of the year, together with tables featuring details on all the
showers currently known to the IMO which produce definite photographic,
radio, telescopic, or visual activity. Although ideally meteor data should be
collected at all times when conditions permit throughout the year, such
protracted monitoring is often not possible, thus the Calendar provides a
ready means of helping to determine when a particular effort may be most
usefully made for those with a restricted observing schedule.
The IMO aims to encourage, collect, analyze, and publish combined meteor data
obtained from sites all over the globe in order to further our understanding
of the meteor activity detectable from the Earth's surface. Results from only
a few localized places can never provide such total comprehension, and it is
solely by the support of many people across the whole world that our
continuing steps towards constructing a true and complete picture of the
near-Earth meteoroid flux can proceed. This means that all meteor workers,
wherever they are and whatever methods they use to record meteors, should
follow the standard IMO observing guidelines when compiling their
information, and submit their data promptly to the appropriate Commission for
analysis.
Visual and photographic techniques have long been popular, and allow nightly
meteor coverage (weather permitting), although both suffer considerably from
the presence of moonlight. Telescopic observations are far less popular,
though they allow the fine detail of shower radiant structures to be derived,
and they permit very low activity showers to be accurately detected. Video
methods are now starting to be taken up, and these have the advantages, and
disadvantages, of both photographic and telescopic observing, but are certain
to increase in importance in the future. Radio receivers can be utilized at
all times, regardless of clouds, moonlight, or daylight, and provide the only
way in which 24-hour meteor observing can be accomplished for most latitudes.
All of these methods used together cover virtually the entire range of
meteoroid sizes, with sufficient overlap between them to allow both accurate
positional data and activity levels to be derived, from the very largest
fireball- producing events (using all-sky photographic patrols or visual
observations) through to tiny dust grains producing extremely faint
telescopic or radio meteors.
Remember that all of the above modes also allow the monitoring of the
continuous background flux of sporadic meteors. Though often treated as of
lesser regard than the showers, the sporadics give an essential calibration
for all other activities, and are furthermore a fascinating subject of study
on their own. However and whenever you are able to observe, we wish you all a
most successful year's work and very much look forward to receiving your
data. Clear skies!
Highlights of the year
======================
In this section, we look at some of the showers especially suitable for
observation this year. Those not dealt with are largely omitted as their main
maxima are badly affected by moonlight, the main casualty in 1995 being the
Perseids, although because of the unpredictable nature of this shower's
outburst maxima in recent years, visual, photographic and radio observers are
urged to be active in any case. Both main peaks are expected between August
12, 13h UT and August 13, 04h UT. Information on special projects, new and
suspected showers can be found in the IMO's bimonthly journal WGN, which
should be regularly consulted for the latest news on all matters meteoric.
Quadrantids
-----------
Active: January 1--5
Maximum: January 3, 23h UT (lambda = 283.16deg)
ZHR = 110
Radiant: alpha = 230deg, delta = +49deg
Radiant drift: Delta\alpha = +0.8deg, Delta\delta= -0.2deg
Diameter: 5deg
V = 41 km/s
r = 2.1 (variable)
TFC: alpha = 242deg, delta = +75deg and
alpha = 198deg, delta = +40deg (beta >40deg N)
PFC: before 00h local time alpha = 150deg, delta = +70deg;
after 00h local time alpha = 180deg, delta = +40deg and
alpha = 240deg, delta = +70deg (beta >40deg N)
Opening the year for northern hemisphere observers is an excellent return of
the Quadrantids, with the Moon a thin waxing crescent at worst. The shower's
radiant is in northern Bootes, and although circumpolar for many northern
sites, is at a useful elevation only after about local midnight. The shower
cannot be sensibly viewed from the southern hemisphere.
The maximum ZHR seems to fluctuate from year to year, though this may be a
result of data collected from too few weather--affected sites in the past,
and the situation is further complicated by the fact that mass-sorting of the
stream appears to cause the fainter (radio and telescopic) meteors to peak up
to around 14 hours before the brighter (visual and photographic) ones.
The actual maximum for any given class of meteors rarely exceeds a few hours
duration however, and can easily be missed. The time of maximum given above
is for visual observations, based on the most reliable series of observations
presently available, obtained by IMO members in 1992. This year affords
another fine opportunity to improve the accuracy of this result still
further. Consequently, all meteoricists should be alert well before and after
this time.
There is some evidence that the radiant size contracts markedly near the peak
and is more diffuse at other times, and photographic observations are
particularly encouraged by the IMO in 1995, with camera work to be carried
out from January 1 to 7 for this purpose. Camera fields should be centred
about 20deg-30deg from the radiant, but not below about 40deg elevation from
the horizon. Photographic meteor rates are liable to be low away from the
shower's peak, but any results obtained away from this period would be doubly
valuable. Accurate visual and telescopic meteor plotting would be welcomed
too.
Alpha-Carinids
--------------
Active: January 24--February 09
Maximum: January 31 (lambda = 311.7deg)
Radiant: alpha= 95deg, delta= -54deg;
diameter: 5deg
V = 25 km/s
r = 2.5
This is one of a number of minor southern hemisphere showers about which very
little is known. Indeed, southern hemisphere meteor astronomy would benefit
from a full survey to establish just which less active showers are genuinely
producing rates at the present time. The current year affords a good
opportunity to observe this particular shower, as new Moon falls on January
30. All forms of observations should be employed for it, with photographic
and telescopic field centres around 20deg to 40deg from the radiant and at
least 40deg from the horizon. The radiant itself, near Canopus (alpha
Carinae), is well above the horizon for most of the night.
Theta-Centaurids
----------------
Active: January 23--Mar 12
Maximum: February 01 (lambda = 312.7deg)
Radiant: alpha = 210deg, delta = -40deg
Radiant drift: Delta\alpha = +1.1deg, Delta\delta = -0.2deg
Diameter: 6deg
V = 60 km/s
r = 2.6
Another minor shower visible only from the southern hemisphere, which is
badly in need of a thorough set of of observations. Its maximum is just a day
after that of the Alpha-Centaurids, so its observing circumstances are very
similar. The main difference is that its radiant elevation improves
throughout the night from about 23h local time, and culminates after dawn.
Photographers and telescopic observers should follow the advice given for the
Alpha-Centaurids above, while visual watchers should carry out standard IMO
plotting watches for best effects.
Lyrids
-------
Active: April 16--25
Maximum: April 22, 15h UT (lambda = 32.1deg)
ZHR: variable---up to 90, usually 15--25
Radiant: alpha = 271deg, delta = +34deg
Radiant drift: Delta\alpha = +1.1deg, Delta\delta = 0.0deg
Diameter: 5deg
V = 49 km/s
r = 2.9
TFC: alpha = 262deg, delta = +16deg and
alpha = 282deg, delta = +19deg (beta >10deg S)
The Lyrids are best viewed from the northern hemisphere, but they are
observable from most sites either north or south of the equator, and are
suitable for all forms of observation. Maximum rates are attained for only
about an hour or two at best, and can be rather erratic at times. In most
years, activity of between 15--25 meteors per hour is seen, but on occasion
much higher rates are noted. The most recent such event was in 1982 when
American observers recorded a very short-lived peak ZHR of 90. This
unpredictability means the Lyrids are always a shower to watch, since we
cannot tell when another unusual return may happen.
As the shower's radiant rises during the night, watches can be usefully
carried out from about 22.30 local time onwards. The peak activity falls with
the Moon at last quarter in 1995, and although the predicted maximum would
appear to favour sites in the western Pacific region and eastern Asia
particularly, the maximum time may be somewhat different to this due to
variations in the stream, so all observers should be alert.
Pi-Puppids
----------
Active: April 15--28
Maximum: April 23, 21h UT (lambda = 33.3deg)
ZHR: periodic---up to around 40
Radiant: alpha = 110deg, delta = -45deg
Radiant drift: Delta\alpha = +0.6deg, Delta\delta = -0.2deg
Diameter: 5deg
V = 18 km/s
r = 2.0
TFC: alpha = 135deg, delta = -55deg and
alpha = 105deg, delta = -25deg (beta <20deg N)
This is a young stream produced by Comet P/Grigg-Skjellerup, and shower
activity has only been detected from it since 1972. Notable short-lived
shower maxima of around 40 meteors per hour occurred in 1977 and 1982---both
years in which the parent comet was at perihelion---but up to 1982, little
activity was seen at other times.
In 1983 however, a ZHR of about 13 was recorded, perhaps suggesting that the
stream has begun to spread further along the comet's orbit, as theory
predicts, so that even though Comet Grigg-Skjellerup is near aphelion in
1995, there is still the possibility of observing a shower from it this year.
The Pi-Puppids are best-seen from the southern hemisphere, with useful
observations mainly possible before local midnight. So far, visual and radio
data have been collected on the shower, but the slow, bright nature of the
meteors make them ideal photographic subjects too. No telescopic data have
been reported in detail as yet either. The Moon will be just past last
quarter for the shower's peak, which means that any shower rates can be
observed by all these techniques with the benefit of a dark sky.
Eta-Aquarids
------------
Active: April 19--May 28
Maximum: May 3, 23h UT (lambda = 43.1deg)
ZHR: 50
Radiant: alpha = 336deg, delta = -02deg,
Radiant drift: Delta\alpha = +0.9deg, Delta\delta = +0.4deg
Diameter: 4deg
V = 66 km/s
r = 2.7
TFC: alpha = 319deg, delta = +10deg and
alpha = 321deg, delta = -23deg (beta < 20deg S)
This is a fine, rich stream associated with Comet P/Halley, like the Orionids
in October, but it is visible for only a few hours before dawn essentially
from tropical and southern hemisphere sites. Occasional meteors have been
reported from further north, and the shower would benefit from increased
observer activity generally. The fast and often bright meteors make the wait
for radiant-rise worthwhile, and many events leave glowing persistent trains
after them. A relatively broad maximum -- sometimes with a variable number of
submaxima -- usually occurs in early May, and activity can be good for
several consecutive nights over this peak. Since new Moon is on April 29 in
1995, the shower will be free from moonlight at its best.
All forms of observing can be used to study the shower, with radio work
allowing activity to be followed even from the northern hemisphere throughout
the daylight morning hours. The radiant culminates at about 8h local time.
Piscis Austrinids
-----------------
Active: July 9--August 17
Maxima: July 29 (lambda = 125.7deg)
ZHR: 8
Radiant: alpha = 341deg, delta = -30deg
Radiant drift: Delta\alpha = +1.0deg, Delta\delta = +0.2deg
Diameter: 5deg
V = 35 km/s
r = 3.2
TFCs: alpha = 255deg to 0deg, delta = 0deg to +15deg,
choose pairs separated by about 30deg in alpha (beta < 30deg N)
Like the Aquarid/Capricornid showers detailed below, this stream is best seen
from near-equatorial or southern hemisphere sites. As Piscis Austrinid
meteors are very similar in appearance to the Aquarids in particular, and
radiate from a similar region of the sky, it is important for visual watchers
to plot all possible shower members. Telescopic observations would also be
very sensible. The new Moon at the end of July is very favourable for the
shower's peak, and from suitable latitudes, the radiant elevation is high for
almost the entire night.
Southern Delta-Aquarids
-----------------------
Active: July 8--August 19
Maximum: July 29, 05h UT (lambda = 125.7deg)
ZHR = 20
Radiant: alpha = 339deg, delta = -16deg
Radiant drift: Delta\alpha, Delta\delta -- see Table 4
Diameter: 5deg
V = 41 km/s
r = 3.2
TFC: alpha = 255deg to 0deg, delta = 0deg to +15deg,
choose pairs separated by about 30deg in alpha (beta >40deg N)
All four Aquarid streams are rich in faint meteors, which makes them well-
suited to telescopic and radio work, but enough brighter members occur to
make visual and even photographic observations possible too. While best
viewing circumstances are to be had from the southern hemisphere, they are
accessible to more northerly sites as well, although they are never
especially impressive from such locations.
The concentration of so many stream radiants in Capricornus and Aquarius at
this time of year often makes shower association difficult, so careful visual
plotting is essential, and observers should be familiar with the approximate
radiant positions for all these showers for any nights observed on. The only
shower likely to produce difficulties in plotting terms is the Southern
Delta-Aquarids near their peak, though the time of their maximum is rather
uncertain, and activity may well be reasonably good for a night or two to
either side of the predicted date. With new Moon on July 27, this shower's
best rates should be well recorded given good skies, since its radiant is
above the horizon all night.
Alpha-Capricornids
------------------
Active: July 3--August 25
Maximum: July 30 (lambda = 126.7deg)
Radiant: alpha = 307deg, delta = -10deg
Radiant drift: Delta\alpha, Delta\delta -- see Table 4
Diameter: 8deg
V = 23 km/s
r = 2.5
TFC: alpha = 255deg to 0deg, delta = 0deg to +15deg,
choose pairs separated by about 30deg in alpha (beta >40deg N)
PFC: alpha = 300deg, delta = +10deg (beta > 45deg N)
alpha = 320deg, delta = -05deg (beta 0deg to 45deg N)
alpha = 300deg, delta = -25deg (beta < 0deg)
This shower has long been noted for its bright -- sometimes fireball-class --
meteors. Their low apparent speed means that they are particularly attractive
to visual and photographic observers. Photographers might like to try
experiments with fragmentation or spectral studies, for example. Although
best observed from more southerly latitudes, those watching from the northern
hemisphere should not ignore the shower. Visual observers south of about
45deg N can usefully make meteor plots certainly. As with the two above
showers, the Alpha-Capricornids benefit from the new Moon near the end of
July this year, and the radiant is close to the zenith around local midnight
from the southern hemisphere.
Kappa-Aquarids
--------------
Active: September 8--30
Maximum: September 21 (lambda = 178.7deg)
ZHR = 3
Radiant: alpha = 339deg, delta = -02deg
Radiant drift: Delta\alpha = +1.0deg, Delta\delta = +0.2deg
Diameter: 5deg
V = 16 km/s
r = 3.0
This minor shower's radiant at its maximum lies near the "Water Jar" asterism
in Aquarius, and consequently is well clear of the horizon for observers
south of about 45deg N all night. It has not been clearly studied, and
further data is badly needed on it. Its meteors are slow and faint, making
them good telescopic targets, and visual meteor plotting should not be too
difficult, again because of the meteors' very low apparent velocity.
Telescopic field centres should be around 20deg to 40deg from the radiant and
at least 40deg above the horizon. As new Moon occurs just three days after
their peak, conditions should be excellent for increasing our knowledge of
this shower in 1995.
Orionids
--------
Active: October 2--November 7
Maximum: October 22 (lambda = 208.4deg)
ZHR=25
Radiant: alpha = 95deg, delta = +16deg
Radiant drift: Delta\alpha = +1.2deg, Delta\delta = +0.1deg
Diameter: 10deg
V = 66 km/s
r = 2.9
TFC: alpha = 100deg, delta = +39deg and
alpha = 75deg, delta = +24deg (beta >40deg N) or
alpha = 80deg, delta = +01deg and
alpha = 117deg, delta = +01deg (beta <40deg N)
On 1993 October 17-18, the Orionids produced a brief but unexpected outburst
of rates equivalent to their normal maximum, some four days before the
predicted peak. The usual maximum then followed in due course around October
21. There is some evidence to suggest this "early maximum" may have been
observed previously, but not in every year, and shows how essential it is to
collect data at times away from known shower peaks. Whether a repeat
performance can be looked for this year we cannot say, but observations,
particularly photographic, telescopic and visual, would be very useful. The
radiant itself has a complex structure, with a number of subradiants, some of
which may be associated with the lesser maxima often reported during the
shower (the 1993 event was an exceptional "lesser peak") and benefits
particularly from telescopic watching. Naked-eye observations are too
inaccurate to properly define the fine radiant structure.
As their radiant is near the celestial equator, the Orionids can be seen from
much of the globe, and observations can be carried out from around midnight
or a little before from most places. Covering the expected main maximum
should present no difficulties in 1995, since the Moon is new on October 24.
Like their May counterpart the Eta-Aquarids, Orionid meteors are swift, can
be bright and are often trained, so they well repay the effort needed to see
them.
Leonids
-------
Active: November 14--21
Maximum: November 18, 08h UT (lambda = 235.57deg)
ZHR: periodic---up to storm levels, recently 10--15
Radiant: alpha = 152deg, delta = +22deg
Radiant drift: Delta\alpha = +0.7deg, Delta\delta = -0.4deg
Diameter: 5deg
V = 71 km/s
r = 2.5
TFC: alpha = 140deg, delta = +35deg and
alpha = 129deg, delta = +06deg (beta > 35deg N) or
alpha = 156deg, delta = -03deg and
alpha = 129deg, delta = +06deg (beta < 35deg N)
The Leonid stream is perhaps most famous for its periodic storms occurring at
roughly 33-year intervals when its associated comet, P/Tempel-Tuttle, returns
to perihelion. This situation is due to happen again in the years 1998--2000,
and Leonid activity is expected to increase in the next few years as the
comet approaches. Clearly, we have the best opportunity ever to follow these
changes in the coming years more fully than has been previously possible, and
to take advantage of these circumstances a special International Leonid Watch
project has been set up with IMO help to coordinate world-wide professional
and amateur Leonid studies. All observing methods should be pursued to ensure
that no detail is missed. Data collection began in 1991, and is intended to
continue into the next century.
In 1995, circumstances are not absolutely ideal, since the Moon will rise
only a couple of hours after the shower radiant at the expected maximum
(radiant rise is around local midnight for most locations north or south of
the equator), but it will at least be a waning crescent in Virgo. Data by all
observing methods is required.
Several unusual returns of this minor stream have occurred, when very short-
lived bursts of high rates have been seen. A ten-year periodicity has been
suggested in these events, which were primarily noted in 1925, 1935 and 1985.
This year would be a good time to try to confirm the reality of the
situation, providing plenty of observers collect and accurately report their
results. The Moon is almost perfectly- placed, just a day before new for the
shower peak. The radiant is available for useful watching from roughly 23h
local time; all observing methods should be employed.
Ursids
------
Active: December 17--26
Maximum: December 22 (lambda = 270.93deg)
ZHR: variable, usually about 15, may reach 50+
Radiant: alpha = 217deg, delta = +75deg
Diameter: 5deg
V = 33 km/s
r = 3.0
TFC: alpha = 348deg, delta = +75deg and
alpha = 131deg, delta = +66deg (beta >40deg N) or
alpha = 63deg, delta = +84deg and
alpha = 156deg, delta = +64deg (beta 30deg to 40deg N)
A northern hemisphere shower which has been very poorly observed, although at
least two major outbursts have occurred within the past 50 years, in 1945 and
1986. Other similar events could easily have been missed however, and we
cannot be certain whether these two outbursts represent a definite
periodicity or not.
Clearly, this is a case where widespread data collection is absolutely vital.
All forms of observation can be made of this shower since many of its meteors
appear to be faint. Unfortunately, so little work has been carried out on the
Ursids that definite statements about what can or cannot be expected from the
shower have no real accuracy.
Although the radiant is circumpolar from almost all northern hemisphere sites
(and thus fails to rise for most southerly ones), it is at its highest later
in the night, culminating after daybreak. New Moon is one day before the peak
this year, so no chance to observe this shower should be wasted.
Abbreviations
=============
- alpha, delta, Delta\alpha, Delta\delta: Coordinates for a shower's radiant
position, usually at maximum; alpha is right ascension, and delta is
declination. Delta indicates the change in either alpha or delta per
day after the peak; + and - signs should be reversed to calculate
radiant positions before this date.
- r : Poplation index, a term computed from each shower's meteor magnitude
distribution. r=2.0--2.5 is brighter than average, while r above 3.0
is fainter than average.
- lambda : Solar longitude, a precise measure of the Earth's position on its
orbit which is not dependent on the vagaries of the calendar. All
lambda are given for the equinox 2000.0.
- V : Atmospheric or apparent meteoric velocity given in km/s. Velocities
range from about 11 km/s (very slow) to 72 km/s (very fast). 40 km/s
is roughly medium speed.
- ZHR: Zenithal Hourly Rate, a calculated maximum number of meteors an ideal
observer would see in a perfectly clear skies with the shower
radiant overhead. This figure is given in terms of meteors per hour.
Storm rates are usually well in excess of 1000 meteors per hour.
Radio ZHRs are based on corrected echo rates, so give only a rough
guide as to what visual activity could be seen in the absence of
daylight. - TFC and PFC: suggested telescopic and photographic field
centers respectively. beta is the observer's latitude ('<' means
``south of'' and '>' means ``north of''). Pairs of telescopic fields
must be observed, alternating about every half hour, so that the
positions of radiants can be defined. The exact choice of TFC or PFC
depends on the observer's location and the elevation of the radiant.
Tables
======
Table 1 -- Working list of visual meteor showers. Streams marked with an
asterisk only produce the indicated ZHR in certain years, and
otherwise produce much lower activity. Contact the IMO's Visual
Commission for more information.
Shower Activity Maximum Radiant
Date lambda alpha delta Diam
(deg) (deg) (deg) (deg)
Quadrantids Jan 01-Jan 05 Jan 03 283.1 230 +49 5
Pi-Puppids II (3) Jan 06-Jan 14 Jan 10 290.7 113 -43 5
Delta-Cancrids Jan 05-Jan 24 Jan 17 296.7 130 +20 10/5
Alpha-Crucids Jan 06-Jan 28 Jan 19 299.7 192 -63 10/5
Lambda-Velids II (3) Jan 18-Jan 26 Jan 21 301.7 133 -46 5
Alpha-Carinids Jan 24-Feb 09 Jan 31 311.7 95 -54 5
Virginids Feb 01-May 30 several Table 2 15/10
Theta-Centaurids Jan 23-Mar 12 Feb 01 312.7 210 -40 6
Alpha-Centaurids * Jan 28-Feb 21 Feb 07 318.7 210 -59 4
Omicron-Centaurids Jan 31-Feb 19 Feb 11 322.7 177 -56 6
Delta-Leonids Feb 05-Mar 19 Feb 15 326.7 159 +19 8
Gamma-Normids Feb 25-Mar 22 Mar 14 353.7 249 -51 5
Beta-Pavonids Mar 11-Apr 16 Apr 07 017.2 308 -63 10/15
Scorpid/Sagittarids (1) Apr 15-Jul 25 several Table 3 15/10
Lyrids * Apr 16-Apr 25 Apr 22 032.1 271 +34 5
Pi-Puppids * Apr 15-Apr 28 Apr 23 033.3 110 -45 5
Alpha-Bootids Apr 14-May 12 Apr 27 036.7 218 +19 8
Eta-Aquarids Apr 19-May 28 May 03 043.1 336 -02 4
Alpha-Scorpids (2) Mar 26-May 12 May 03 043.4 240 -27 5
Ophiuchids N (2) Apr 25-May 31 May 10 049.7 249 -14 5
Beta-Corona Australids(2) Apr 23-May 30 May 15 054.7 284 -40 5
Kappa-Scorpids (2) May 04-May 27 May 19 058.9 267 -39 5
Ophiuchids S (2) May 13-May 26 May 20 059.8 258 -24 5
Omega-Scorpids (2) May 23-Jun 15 Jun 04 074.2 243 -22 5
Chi-Scorpids (2) May 24-Jun 20 Jun 05 075.2 248 -14 6
Gamma-Sagittarids (2) May 22-Jun 13 Jun 06 076.1 272 -28 6
Theta-Ophiuchids (2) Jun 04-Jul 15 Jun 13 082.4 267 -20 5
Lyrids (Jun) Jun 11-Jun 21 Jun 16 085.2 278 +35 5
Bootids (Jun) Jun 26-Jun 30 Jun 28 096.3 219 +49 8
Lambda-Sagittarids (2) Jun 05-Jul 25 Jul 01 099.6 276 -25 6
Pegasids Jul 07-Jul 11 Jul 10 107.7 340 +15 5
Phoenicids (Jul) Jun 24-Jul 18 Jul 15 112.7 021 -43 7
Piscis Austrinids Jul 09-Aug 17 Jul 29 125.7 341 -30 5
Delta-Aquarids S Jul 08-Aug 19 Jul 29 125.7 339 -16 5
Alpha-Capricornids Jul 03-Aug 25 Jul 30 126.7 307 -10 8
Iota-Aquarids S Jul 15-Aug 25 Aug 04 131.7 333 -15 5
Delta-Aquarids N Jul 15-Aug 25 Aug 12 139.7 337 -05 5
Perseids Jul 17-Aug 24 Aug 12 139.5 046 +58 5
Kappa-Cygnids Aug 03-Aug 31 Aug 19 145.7 286 +59 6
Iota-Aquarids N Aug 11-Sep 20 Aug 20 147.7 327 -06 5
Pi-Eridanids Aug 20-Sep 05 Aug 29 155.7 052 -15 6
Alpha-Aurigids Aug 24-Sep 05 Sep 01 158.6 084 +42 5
Delta-Aurigids Sep 05-Oct 10 Sep 09 166.7 060 +47 5
Piscids Aug 15-Oct 14 Sep 20 177.7 008 00 8
Kappa-Aquarids Sep 08-Sep 30 Sep 21 178.7 339 -02 5
Puppid/Velids Sep 28-Dec 30 several Table 5 10
Capricornids (Oct) Sep 20-Oct 14 Oct 03 189.7 303 -10 5
Sigma-Orionids Sep 10-Oct 26 Oct 05 191.7 086 -03 5
Draconids * Oct 06-Oct 10 Oct 10 197.0 262 +54 5
Epsilon-Geminids Oct 14-Oct 27 Oct 20 206.7 104 +27 5
Orionids Oct 02-Nov 07 Oct 22 208.4 095 +16 10
Taurids S Sep 15-Nov 25 Nov 03 220.7 050 +14 10/5
Taurids N Sep 13-Nov 25 Nov 13 230.7 060 +23 10/5
Leonids * Nov 14-Nov 21 Nov 18 235.6 152 +22 5
Alpha-Monocerotids Nov 15-Nov 25 Nov 21 239.4 117 -06 5
Chi-Orionids Nov 26-Dec 15 Dec 02 250.0 082 +23 8
Phoenicids (Dec) * Nov 28-Dec 09 Dec 06 254.3 018 -53 5
Sigma-Puppids II (3) Nov 27-Dec 12 Dec 06 254.7 102 -45 5
Monocerotids (Dec) Nov 27-Dec 17 Dec 10 258.7 100 +14 5
Sigma-Hydrids Dec 03-Dec 15 Dec 11 259.7 127 +02 5
Geminids Dec
Žensko
Muško
Nebitno
, najviše će se vidjeti u noći s 11 na 12 i s 12 na 13 i to pred jutro, negdje oko 3-4 sata. Ekipicu i na promatranje 
