View Full Version : Names of Stars and Exoplanets

2015-Jul-25, 05:55 AM
Where do stars' names come from?

The brightest stars have individual names like Sirius (Greek seirios: "scorcher"). Many of them have names related to what part of the constellation or asterism that they are in, like Denebola (Arabic dhanab al asad: "tail of the lion"). There are some other stars with "Deneb" in their names, those names referring to the tail of something.

But that system has its limits, and in 1609, Johann Bayer decided on a simpler system: (number as Greek letter) of (constellation) where the stars are listed in order of apparent brightness. The of-constellation part is done using the Latin genitive or of-case.

Sirius in it is Alpha Canis Majoris or α CMa, where "Canis Majoris" is the genitive of "Canis Major": "Big Dog". In English, it would be Alpha of the Big Dog.

In 1712, Edmond Halley and Isaac Newton published John Flamsteed's catalog of stars without his permission. In that catalog, JF had listed stars as (number) of (constellation), where the number increases from west to east, in increasing "right ascension" (sort of like longitude).

Sirius in it is 9 Canis Majoris, #9 of the Big Dog.

More recent star cataloguers have not bothered with constellation locations. Thus, Sirius is:

HD 48915 -- Henry Draper Catalog #48915
HR 2491 -- Harvard Revised or Yale Bright Star Catalog #2491
BD −161591 -- Bonner Durchmunsterung (German: "Bonn Survey") star #1591 in declination (sort of like latitude) zone -16d to -17d.
GJ 244 A/B -- Gliese-Jahreiss catalog, or Gliese Catalog of Nearby Stars #244 with stars A and B
GCTP 1577.00 A/B -- the General Catalog of Trigonometric Parallaxes
HIP 32349 -- Hipparcos astrometric-satellite catalog #32349
ADS 5423 -- Aitken's Double-Star Catalog #5423
LTT 2638 -- Luyten Two-Tenths catalog #2638

Some notable stars still get individual names, like Barnard's Star and Kapteyn's Star, after some astronomers who discovered notable features of them.

I won't get into Solar-System nomenclature, but I will do exoplanets.

JPL | Videos | Q and Alien: What's in an Exoplanet Name? (http://www.jpl.nasa.gov/video/details.php?id=1340) also at ▶ Q&Alien: What’s in an Exoplanet Name? - YouTube (https://www.youtube.com/watch?v=iL48DLbA4OI)

Names like Kepler-7b, HD 189733b, GJ 1214b, Gliese 581g, Kapteyn b, Gliese 667 Cc, ...

Why not names like Wu Tang Clan or Ghostface or Alderaan or Gallifrey? For starters, astronomers have discovered a *lot* of exoplanets, and giving them individual names would be a lot of trouble. Also, their names have a certain descriptive value:
(star) + (planet letter)
(star) is typically (catalog) + (number), like most of my examples.
Thus, Kepler-7 is the 7th star that the Kepler team has discovered to have planets.

The first planet named is small-letter b, because "a" is reserved for its star. They are named in order of discovery, and if several are discovered at the same time, they are then named in order of distance.

Stars, however, have capital letters: A, B, C, ... in order of brightness or discovery.

Using ease of observation as a proxy for discovery order for pre-telescopically observed objects, the Solar System would have this naming:

A: Sun
b: Earth
bb: Moon
c: Venus
d: Jupiter
e: Mars
f: Saturn
g: Mercury
db: Io
dc: Europa
dd: Ganymede
de: Callisto
fb: Titan
h: Uranus

No exomoons have been discovered yet, but I've extended the planet nomenclature to moons. The Solar System's numerous small objects present a big problem for this scheme, so I've ignored comets.

Finally, Naming of exoplanets | IAU (http://www.iau.org/public/themes/naming_exoplanets/) by the International Astronomical Union. That page gives some guidelines for proposed names and name contests.