Remarks, Abbreviations, Tables for 2005

Radiant sizes and meteor plotting

by Rainer Arlt

If you are not observing during a major-shower maximum, it is essential to associate meteors with their radiants correctly, since the total number of meteors will be small for each source. Meteor plotting allows shower association by more objective criteria after your observation than the simple imaginary back-prolongation of paths under the sky. With meteors plotted on gnomonic maps, you can trace them back to their radiants by extending their straight line paths. If a radiant lies on another chart, you should find common stars on an adjacent chart to extend this back-prolongation correctly.

How large a radiant should be assumed for shower association? The real physical radiant size is very small, but visual plotting errors cause many true shower meteors to miss this real radiant area. Thus we have to assume a larger effective radiant to allow for these errors. Unfortunately, as we enlarge the radiant, so more and more sporadic meteors will appear to line up accidentally with this region. Hence we have to apply an optimum radiant diameter to compensate for the plotting errors loss, but which will not then be swamped by sporadic meteor pollution. Table 1 gives this optimum diameter as a function of the distance of the meteor from the radiant.

Table 1 - Optimum radiant diameters ("Diameter") to be assumed for shower association of minor-shower meteors as a function of the radiant distance ("D") of the meteor.

The path-direction is not the only criterion for shower association. The angular velocity of the meteor should match the expected speed of the given shower meteors according to their geocentric velocities. Angular velocity estimates should be made in degrees per second (°/s). To do this, make the meteors you see move for one second in your imagination at the speed you saw them. The path length of this imaginary meteor is the angular velocity in °/s. Note that typical speeds are in the range 3°/s to 25°/s. Typical errors for such estimates are given in Table 2.

Table 2 - Error limits for the angular velocity.

If you find a meteor in your plots which passes the radiant within the diameter given by Table 1, check its angular velocity. Table 3 gives the angular speeds for a few geocentric velocities, which can then be looked up in Table 5 for each shower.

Angular velocities as a function of the radiant distance of the meteor (D) and the elevation of the meteor above the horizon (h) for three different atmospheric entry velocities (v_infty). All angular velocities are in °/s.

Table 3 - Angular velocities as a function of the radiant distance of the meteor (D) and the elevation of the meteor above the horizon (h) for three different atmospheric entry velocities (v_infty). All angular velocities are in °/s.

Abbreviations

• α, δ: Coordinates for a shower's radiant position, usually at maximum. α is right ascension, δ is declination. Radiants drift across the sky each day due to the Earth's own orbital motion around the Sun, and this must be allowed for using the details in Table 6 for nights away from the listed shower maxima.

• r: The population 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.

• sol: Solar longitude, a precise measure of the Earth's position on its orbit which is not dependent on the vagaries of the calendar. All sol are given for the equinox J2000.0.

• v_infty: Atmospheric or meteoric entry 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 perfectly clear skies with the shower radiant overhead. This figure is given in terms of meteors per hour. Where meteor activity persisted at a high level for less than an hour, an equivalent ZHR (EZHR) is used measuring the activity as if it would have lasted for an hour.

• TFC and PFC: Suggested telescopic and small-camera photographic field centers respectively. β 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. Note that the TFCs are also useful centers to use for video camera fields as well.

Lunar phases for 2005.

Working list of visual meteor showers.

Details in this Table were correct according to the best information available in May 2005. Contact the IMO's Visual Commission for more information. Maximum dates in parentheses indicate reference dates for the radiant, not true maxima. Some showers have ZHRs that vary from year to year. The most recent reliable figure is given here, except for possibly periodic showers that are noted as "var." = variable. An asterisk ("*") in the "sol" column indicates the shower may have other or additional peak times, noted in the text.

Radiant drift positions during the year in α and δ.

  
    COM  DCA  QUA  
  Jan 0 186 +20 112 +22 228 +50  
  Jan 5 190 +18 116 +22 231 +49  
  Jan 10 194 +17 121 +21  
  Jan 20 202 +13 130 +19   ACE  VIR  
  Jan 30       200 -57 157 +16 DLE  
  Feb 10       214 -60 165 +10 155 +20 GNO  
  Feb 20       225 -63 172 +6 164 +18 225 -53  
  Feb 28         178 +3 171 +15 234 -52  
  Mar 10         186 0 180 +12 245 -51  
  Mar 20         192 -3   256 -50  
  Mar 30         198 -5  
  Apr 10 SAG  LYR  PPU   203 -7  
  Apr 15 224 -17 263 +34 106 -44 ETA 205 -8  
  Apr 20 227 -18 269 +34 109 -45 323 -7  
  Apr 25 230 -19 274 +34 111 -45 328 -5  
  Apr 30 233 -19     332 -4  
  May 5 236 -20     337 -2  
  May 10 240 -21     341 0  
  May 20 247 -22     350 +5  
  May 30 256 -23  
  Jun 10 265 -23  
  Jun 15 270 -23  
  Jun 20 275 -23 JBO  
  Jun 25 280 -23 223 +48  
  Jun 30 284 -23 225 +47 CAP      JPE  
  Jul 5 289 -22   285 -16 SDA   338 +14  
  Jul 10 293 -22 PHE 289 -15 325 -19 NDA 341 +15 PER  PAU  
  Jul 15 298 -21 032 -48 294 -14 329 -19 316 -10   012 +51 330 -34  
  Jul 20     299 -12 333 -18 319 -9 SIA 018 +52 334 -33  
  Jul 25     303 -11 337 -17 323 -9 322 -17 023 +54 338 -31  
  Jul 30 KCG   308 -10 340 -16 327 -8 328 -16 029 +55 343 -29  
  Aug 5 283 +58 NIA 313 -8 345 -14 332 -6 334 -15 037 +57 348 -27  
  Aug 10 284 +58 317 -7 318 -6 349 -13 335 -5 339 -14 043 +58 352 -26  
  Aug 15 285 +59 322 -7   352 -12 339 -4 345 -13 050 +59  
  Aug 20 286 +59 327 -6 AUR 356 -11 343 -3   057 +59  
  Aug 25 288 +60 332 -5 076 +42   347 -2   065 +60  
  Aug 30 289 +60 337 -5 082 +42 DAU  
  Sep 5     088 +42 055 +46 SPI  
  Sep 10     092 +42 060 +47 357 -5  
  Sep 15       066 +48 001 -3  
  Sep 20       071 +48 005 -1  
  Sep 25 NTA  STA   077 +49 009 0  
  Sep 30 021 +11 023 +5 ORI 083 +49 013 +2  
  Oct 5 025 +12 027 +7 085 +14 089 +49   GIA  
  Oct 10 029 +14 031 +8 088 +15 095 +49 EGE 262 +54  
  Oct 15 034 +16 035 +9 091 +15   099 +27  
  Oct 20 038 +17 039 +11 094 +16   104 +27  
  Oct 25 043 +18 043 +12 098 +16   109 +27  
  Oct 30 047 +20 047 +13 101 +16  
  Nov 5 053 +21 052 +14 105 +17  
  Nov 10 058 +22 056 +15   LEO  AMO  
  Nov 15 062 +23 060 +16   150 +23 112 +2  
  Nov 20 067 +24 064 +16 XOR 153 +21 116 +1  
  Nov 25 072 +24 069 +17 075 +23   120 0 MON  PUP  PHO  
  Nov 30     080 +23 HYD   091 +8 120 -45 014 -52  
  Dec 5 COM  GEM 085 +23 122 +3   096 +8 122 -45 018 -53  
  Dec 10 169 +27 108 +33 090 +23 126 +2   100 +8 125 -45 022 -53  
  Dec 15 173 +26 113 +33 094 +23 130 +1 URS 104 +8 128 -45  
  Dec 20 177 +24 118 +32     217 +75  
  

Working list of daytime radio meteor streams.

The "Best Observed" columns give the approximate local mean times between which a four-element antenna at an elevation of 45° receiving a signal from a 30-kW transmitter 1000 km away should record at least 85% of any suitably positioned radio-reflecting meteor trails for the appropriate latitudes. Note that this is often heavily dependent on the compass direction in which the antenna is pointing, however, and applies only to dates near the shower's maximum.

Useful addresses

For more information on observing techniques, and when submitting results, please contact the appropriate IMO Commission Director:

• Fireball Data Center (FIDAC): André Knöfel, Habichtstr. 1, D-15526 Reichenwalde, Germany.

• Photographic Commission: Marc de Lignie, Prins Hendrikplein 42, NL-2264 SN Leidschendam, The Netherlands.

• Radio Commission: Temporarily vacant. e-mail: radio@imo.net

• Telescopic Commission: Malcolm Currie, 25 Collett Way, Grove, Wantage, Oxfordshire, OX12,0NT, UK.

• Video Commission: Sirko Molau, Abenstalstrasse 13b, D-84072 Seysdorf, Germany.

• Visual Commission: Rainer Arlt, Friedenstrasse 5, D-14109 Potsdam, Germany.

Please try to enclose return postage when writing to any IMO officials, either in the form of stamps (same country only) or as an International Reply Coupon (I.R.C. - available from main postal outlets). Thank you!