"Official" Astronomical Names
Astronomy is an old science. Its nomenclature is often derived from tradition
(especially Greek/Roman mythology)
rather than from what might today seem more sensible. The names of the objects in
the solar system are particularly so.
International Astronomical Union
(IAU) is officially in charge of assigning
astronomical names and it is very sensitive to astronomical tradition.
in our solar system get
a name as soon as possible. There aren't likely to be any new ones until
we see them around another star. Who knows what convention will be used
Satellites of the planets
are assigned a provisional designation
(indicating year of discovery)
by the Central Bureau for Astronomical Telegrams
upon satisfactory demonstration of the existence of a new object.
when Voyager 2 found a bunch of new moons
in its 1989 Neptune encounter, they were named
S/1989 N 1, S/1989 N 2, etc.
When the orbit of the new object is accurate enough to allow
the prediction of future positions with reasonable precision, the object is
assigned a Roman numeral (e.g. Neptune VIII),
and the object may receive a name (e.g. Proteus).
(The name is suggested by the
discoverer(s), but following tradition is strongly encouraged; so if you
want to name a planet or satellite, get out your
books of mythology.
that the moons of Uranus are a special case -- they get
literary instead of mythological names.) This process is currently underway
for the new Uranian moons discovered recently.
are at first given provisional numbers by the
Minor Planet Center (MPC)
indicating the year and month of discovery.
The provisional designation is the year, followed by a letter that indicates
the half-month during which the discovery occurred, followed by a letter that
indicates sequence within the half-month. So 1982 DB was reported in the last
half of February 1982, and it's the second asteroid discovered during that
period. When their orbits are
understood well enough that their future position can be predicted
well, they are given a permanent number and name.
"243 Ida" is the 243rd
asteroid to be numbered (not necessarily the 243rd discovered).
The name is again chosen by the discoverer, but
there's much more latitude; asteroids can be named after a living
person, or almost anything else (e.g. "2309 Mr. Spock"; several have been named for
Final decisions are made by an IAU committee.
For more information see
"How Are Minor Planets Named?".
In the past, Comets were first given a provisional
of the year and a lowercase letter indicating the order of discovery in the
year (e.g., 1994a was the first comet discovered or recovered in 1994,
1994b the second, etc.). The name was also assigned at an early stage. Up
to three (preferably independent) discoverers may have been attached to the
comet. Some time later, the comets that had passed
perihelion in a given year were assigned Roman numeral designations
indicating the order of perihelion passage within the year. The Roman
numeral designations for 1993 and 1994 are given in the Jan. 1995
batch of Minor Planet Circulars (MPCs).
Note that whole comet designation system was revamped starting in the
beginning of 1995. The main points of the new scheme are:
The new scheme was backdated, so old comets received new-style
There is an
between old- and new-style comet designations.
- the provisional designation system now closely matches the
designation system for minor planets. The first comet discovered
in the first half of 1995 Jan. is designated 1995 A1, the
second 1995 A2, etc.
- long-period comets and one-apparition periodic comets receive only
a provisional designation -- there is no equivalent of the
Roman numeral designation.
- upon recovery at a second apparition (or following through aphelion)
periodic comets receive a sequential number. E.g., P/Halley
- routine recoveries of periodic comets do not receive provisional
- the nature of the comet orbit is indicated by a prefix:
P/ for periodic comets, C/ for long-periodic comets, D/ for
defunct comets (e.g., 1993e) and X/ for uncertain comets.
Additionally, A/ is used to indicate that the object
is a minor planet.
- comets continue to be named in general terms for their
discoverers ensuring fairness and simplicity.
- Provisional comet designations are assigned by
the CBAT. Permanent comet numbers are assigned by
the Minor Planet Center.
Some examples of new comet designations:
C/1995 Q2 (Hartley-Drinkwater)
P/1994 P1-A (Machholz 2) Fragment A of a split comet
P/1996 A1 (Jedicke) New periodic comet
125P Routine observation of periodic comet
Here is a copy of the official
Landscape features on planets, satellites, and asteroids follow
complicated conventions set by the IAU Nomenclature Committee.
Among these are the restriction that a planetary feature may not bear the name
of a living person or of a political or religious figure from the last 200
A good explanation of this may be
found in *Planetary Mapping*, edited by Greeley & Batson Cambridge
U.Press, 1990. (Gee, it's handy having Phil Stooke's
Planetary Map FAQ
lying around on my disk!)
[ Adapted from usenet postings by Bill Higgins and Gareth Williams but any errors
are mine. ]
This site contains detailed information about all names of topographic
and albedo features on planets and satellites (and some planetary ring
and ring-gap systems) that the International Astronomical Union (IAU)
has named and approved.
Bill Arnett; last updated:
2000 Jan 14
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