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.
| D | Diameter |
|---|---|
| 15° | 14° |
| 30° | 17° |
| 50° | 20° |
| 70° | 23° |
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.
| Angular velocity (°/s) | 5 | 10 | 15 | 20 | 30 |
|---|---|---|---|---|---|
| Permitted error (°/s) | 3 | 5 | 6 | 7 | 8 |
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.
| v_infty=25 km/s | v_infty=40 km/s | v_infty=60 km/s | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| D | 10° | 20° | 40° | 60° | 90° | 10° | 20° | 40° | 60° | 90° | 10° | 20° | 40° | 60° | 90° |
| 10° | 0.4 | 0.9 | 1.6 | 2.2 | 2.5 | 0.7 | 1.4 | 2.6 | 3.5 | 4.0 | 0.9 | 1.8 | 3.7 | 4.6 | 5.3 |
| 20° | 0.9 | 1.7 | 3.2 | 4.3 | 4.9 | 1.4 | 2.7 | 5.0 | 6.8 | 7.9 | 1.8 | 3.5 | 6.7 | 9.0 | 10 |
| 40° | 1.6 | 3.2 | 5.9 | 8.0 | 9.3 | 2.6 | 5.0 | 9.5 | 13 | 15 | 3.7 | 6.7 | 13 | 17 | 20 |
| 60° | 2.2 | 4.3 | 8.0 | 11 | 13 | 3.5 | 6.8 | 13 | 17 | 20 | 4.6 | 9.0 | 17 | 23 | 26 |
| 90° | 2.5 | 4.9 | 9.3 | 13 | 14 | 4.0 | 7.9 | 15 | 20 | 23 | 5.3 | 10 | 20 | 26 | 30 |
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.
| New Moon | First Quarter | Full Moon | Last Quarter |
|---|---|---|---|
| January 3 | |||
| January 10 | January 17 | January 25 | February 2 |
| February 8 | February 16 | February 24 | March 3 |
| March 10 | March 17 | March 25 | April 2 |
| April 8 | April 16 | April 24 | May 1 |
| May 8 | May 16 | May 23 | May 30 |
| June 6 | June 15 | June 22 | June 28 |
| July 6 | July 14 | July 21 | July 28 |
| August 5 | August 13 | August 19 | August 26 |
| September 3 | September 11 | September 18 | September 25 |
| October 3 | October 10 | October 17 | October 25 |
| November 2 | November 9 | November 16 | November 23 |
| December 1 | December 8 | December 15 | December 23 |
| December 31 |
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.
| Shower | Activity Period | Maximum | Radiant | V_infty | r | ZHR | ||
|---|---|---|---|---|---|---|---|---|
| Date | sol | α | δ | km/s | ||||
| Quadrantids (QUA) | Jan 01-Jan 05 | Jan 03 | 283°16 | 230° | +49° | 41 | 2.1 | 120 |
| δ-Cancrids (DCA) | Jan 01-Jan 24 | Jan 17 | 297° | 130° | +20° | 28 | 3.0 | 4 |
| α-Centaurids (ACE) | Jan 28-Feb 21 | Feb 07 | 319°2 | 210° | -59° | 56 | 2.0 | 6 |
| δ-Leonids (DLE) | Feb 15-Mar 10 | Feb 24 | 336° | 168° | +16° | 23 | 3.0 | 2 |
| γ-Normids (GNO) | Feb 25-Mar 22 | Mar 13 | 353° | 249° | -51° | 56 | 2.4 | 8 |
| Virginids (VIR) | Jan 25-Apr 15 | (Mar 24) | (4°) | 195° | -04° | 30 | 3.0 | 5 |
| Lyrids (LYR) | Apr 16-Apr 25 | Apr 22 | 032°32 | 271° | +34° | 49 | 2.1 | 18 |
| π-Puppids (PPU) | Apr 15-Apr 28 | Apr 24 | 033°5 | 110° | -45° | 18 | 2.0 | var |
| η-Aquarids (ETA) | Apr 19-May 28 | May 05 | 045°5 | 338° | -01° | 66 | 2.4 | 60 |
| Sagittarids (SAG) | Apr 15-Jul 15 | (May 19) | (59°) | 247° | -22° | 30 | 2.5 | 5 |
| June Bootids (JBO) | Jun 26-Jul 02 | Jun 27 | 095°7 | 224° | +48° | 18 | 2.2 | var |
| Pegasids (JPE) | Jul 07-Jul 13 | Jul 09 | 107°5 | 340° | +15° | 70 | 3.0 | 3 |
| July Phoenicids (PHE) | Jul 10-Jul 16 | Jul 13 | 111° | 32° | -48° | 47 | 3.0 | var |
| Piscis Austrinids (PAU) | Jul 15-Aug 10 | Jul 28 | 125° | 341° | -30° | 35 | 3.2 | 5 |
| South. δ-Aquarids (SDA) | Jul 12-Aug 19 | Jul 28 | 125° | 339° | -16° | 41 | 3.2 | 20 |
| α-Capricornids (CAP) | Jul 03-Aug 15 | Jul 30 | 127° | 307° | -10° | 23 | 2.5 | 4 |
| South. ι-Aquarids (SIA) | Jul 25-Aug 15 | Aug 04 | 132° | 334° | -15° | 34 | 2.9 | 2 |
| North. δ-Aquarids (NDA) | Jul 15-Aug 25 | Aug 08 | 136° | 335° | -05° | 42 | 3.4 | 4 |
| Perseids (PER) | Jul 17-Aug 24 | Aug 12 | 140° | 46° | +58° | 59 | 2.6 | 100 |
| κ-Cygnids (KCG) | Aug 03-Aug 25 | Aug 17 | 145° | 286° | +59° | 25 | 3.0 | 3 |
| North. ι-Aquarids (NIA) | Aug 11-Aug 31 | Aug 19 | 147° | 327° | -06° | 31 | 3.2 | 3 |
| α-Aurigids (AUR) | Aug 25-Sep 08 | Sep 01 | 158°6 | 84° | +42° | 66 | 2.6 | 7 |
| δ-Aurigids (DAU) | Sep 05-Oct 10 | Sep 09 | 166°7 | 60° | +47° | 64 | 2.9 | 5 |
| Piscids (SPI) | Sep 01-Sep 30 | Sep 19 | 177° | 5° | -01° | 26 | 3.0 | 3 |
| Draconids (GIA) | Oct 06-Oct 10 | Oct 08 | 195°4 | 262° | +54° | 20 | 2.6 | var |
| ε-Geminids (EGE) | Oct 14-Oct 27 | Oct 18 | 205° | 102° | +27° | 70 | 3.0 | 2 |
| Orionids (ORI) | Oct 02-Nov 07 | Oct 21 | 208° | 95° | +16° | 66 | 2.5 | 23 |
| Southern Taurids (STA) | Oct 01-Nov 25 | Nov 05 | 223° | 52° | +13° | 27 | 2.3 | 5 |
| Northern Taurids (NTA) | Oct 01-Nov 25 | Nov 12 | 230° | 58° | +22° | 29 | 2.3 | 5 |
| Leonids (LEO) | Nov 14-Nov 21 | Nov 17 | 235°27 | 153° | +22° | 71 | 2.5 | 20+ |
| α-Monocerotids (AMO) | Nov 15-Nov 25 | Nov 21 | 239°32 | 117° | +01° | 65 | 2.4 | var |
| χ-Orionids (XOR) | Nov 26-Dec 15 | Dec 02 | 250° | 82° | +23° | 28 | 3.0 | 3 |
| Dec Phoenicids (PHO) | Nov 28-Dec 09 | Dec 06 | 254°25 | 18° | -53° | 18 | 2.8 | var |
| Puppid/Velids (PUP) | Dec 01-Dec 15 | (Dec 07) | (255°) | 123° | -45° | 40 | 2.9 | 10 |
| Monocerotids (MON) | Nov 27-Dec 17 | Dec 09 | 257° | 100° | +08° | 42 | 3.0 | 3 |
| σ-Hydrids (HYD) | Dec 03-Dec 15 | Dec 12 | 260° | 127° | +02° | 58 | 3.0 | 2 |
| Geminids (GEM) | Dec 07-Dec 17 | Dec 14 | 262°2 | 112° | +33° | 35 | 2.6 | 120 |
| Coma Berenicids (COM) | Dec 12-Jan 23 | Dec 19 | 268° | 175° | +25° | 65 | 3.0 | 5 |
| Ursids (URS) | Dec 17-Dec 26 | Dec 22 | 270°7 | 217° | +76° | 33 | 3.0 | 10 |
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.
| Shower | Activity | Max Date | sol 2000.0 | Radiant | Best Observed | Rate | ||
|---|---|---|---|---|---|---|---|---|
| α | δ | 50°N | 35°S | |||||
| Cap/Sagittarids | Jan 13-Feb 04 | Feb 01 | 312.5° | 299° | -15° | 11h-14h | 09h-14h | medium |
| χ-Capricornids | Jan 29-Feb 28 | Feb 13 | 324.7° | 315° | -24° | 10h-13h | 08h-15h | low |
| Piscids (Apr) | Apr 08-Apr 29 | Apr 20 | 30.3 ° | 7° | +07° | 07h-14h | 08h-13h | low |
| δ-Piscids | Apr 24-Apr 24 | Apr 24 | 34.2 ° | 11° | +12° | 07h-14h | 08h-13h | low |
| ε-Arietids | Apr 24-May 27 | May 09 | 48.7 ° | 44° | +21° | 08h-15h | 10h-14h | low |
| Arietids (May) | May 04-Jun 06 | May 16 | 55.5 ° | 37° | +18° | 08h-15h | 09h-13h | low |
| ο-Cetids | May 05-Jun 02 | May 20 | 59.3 ° | 28° | -04° | 07h-13h | 07h-13h | medium |
| Arietids | May 22-Jul 02 | Jun 07 | 76.7 ° | 44° | +24° | 06h-14h | 08h-12h | high |
| ζ-Perseids | May 20-Jul 05 | Jun 09 | 78.6 ° | 62° | +23° | 07h-15h | 09h-13h | high |
| β-Taurids | Jun 05-Jul 17 | Jun 28 | 96.7 ° | 86° | +19° | 08h-15h | 09h-13h | medium |
| γ-Leonids | Aug 14-Sep 12 | Aug 25 | 152.2° | 155° | +20° | 08h-16h | 10h-14h | low |
| Sextantids | Sep 09-Oct 09 | Sep 27 | 184.3° | 152° | 00° | 06h-12h | 06h-13h | medium |
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!