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 AD 2020, September 27
 R. Rudawska
 T.J. Jopek

Nomenclature Rules for Meteor Showers

The following nomenclature rules are adopted for meteor showers, keeping in mind that it is not always known precisely during discovery when is the peak of a meteor shower and what is the position of the radiant at that time. For known showers, the Working Group may choose a traditionally accepted name (e.g., alpha-Monocerotids) over the more correct name after a radiant has been established (which would have suggested the name of delta-Canis Minorids).

The general rule is that a meteor shower (and a meteoroid stream) should be named after the constellation that contains the nearest star to the radiant point, using the possessive Latin form. The possessive Latin name for the constellations end in one of seven declensions:

  • ae (e.g., Lyrae),
  • is (e.g., Leonis),
  • i (e.g., Ophiuchi),
  • us (e.g.,Doradus),
  • ei (e.g., Equulei),
  • ium (e.g., Piscium), or
  • orum (e.g., Geminorum).

Custom is to replace the final suffix for '-id', or plural '-ids'. Meteors from Aquarius (Aquarii) are Aquariids, not Aquarids. An exception is made for meteors from the constellation of Hydrus,which will be called 'Hydrusids', in order not to confuse with meteors from the constellation of Hydra.

When the constellation name has two parts, only the second declension is to be replaced by 'id'. Hence, meteors from Canes Venatici (Canum Venaticorum) would be 'Canum Venaticids'. When two constellations are grouped together, a bracket is used and both constellation names will have 'id'. Hence, Puppids-Velids. As a guideline, the order of the constellations should be in the same sequence as the radiant daily motion.

If a higher precision is needed, then the shower is named after the nearest (if in doubt: brightest) star with a Greek letter assigned, as first introduced in the Uranometria atlas by Johann Bayer (1603), or one with a later introduced Roman letter. If in doubt, the radiant position at the time of the peak of the shower (in the year of discovery) should be taken. Hence, the meteors of comet IRAS-Araki-Alcock would be named 'eta-Lyrids'.
In that case, if a meteor shower radiant is near the border of a constellation and the nearest such star is in the neighboring constellation, then the shower is named after that star.

Following existing custom, one may add the name of the month to distinguish among showers from the same constellation. In this case, one could call the shower from comet IRAS-Araki-Alcock the 'May Lyrids', in order to differentiate from the more familiar 'April Lyrids'.

For daytime showers, it is custom to add 'Daytime', hence the name for the 'Daytime Arietids' in June as opposed to the Arietids in October. As a guideline, the stream radiant should be less than 32 degs from the Sun to be called a daytime shower. This ensures that no where is the radiant more than 20 degs above the horizon at the start of local Nautical twilight.

South and North refer to 'branches' of a shower south and north of the ecliptic plane (stricktly the orbital plane of Jupiter), resulting from meteoroids of the same (original) parent body. Because they have nearly the same longitude of perihelion at a given solar longitude (the argument of perihelion and longitude of ascending node differing by 180 degrees between South and North), the two branches are active over about the same time period.

If the meteoroid stream is encountered at the other node, it is customary to speak of 'twin showers'. The Orionids and eta-Aquariids are twin showers, even though each represent dust deposited at different times and are now in quite different orbits. As a matter of custom, twin showers and the north and south branches of a stream carry different names. Meteor showers are not to be named after their parent bodies (e.g., Giacobinids, IRAS-Araki-Alcockids). The names of comets tend not to be Latin, making the naming not unique. Also, comet names can change when they get lost and are recovered.

The Working Group for Meteor Shower Nomenclature will choose among possible alternative proposed names for newly identified meteor showers, in order to establish a unique name for each meteor shower (e.g., eta-Lyrids, not May Lyrids).