Z. Celestial Objects

Z: Celestial Objects [This class is based on the compiler's reading in a field far from his expertise. But there seems to be considerable consensus, except as noted.]

Note: the atmosphere of Earth is captured under N.

ZD. Dark matter The BCC generally excludes unobserved phenomena, but an exception may be warranted here. Dark matter is defined as matter which emits no light or other identifiable radiation.

ZN. Nebulae While the term .nebula' once referred to diverse astronomical phenomena, including galaxies, its more modern usage is to refer to clouds of dust and gas. These may represent the results of an exploded star or they may be in the process of collapsing into a star. There are a handful of commonly recognized types.

1. clouds, diffuse nebulae

2. planetary nebulae

3. Proto-planetary nebulae

4. Supernova remnants

5. Dark nebulae

Some dozens of nebulae have been named of each type. These might be designated with Cutter numbers (especially as discovery continues).

Since nebulae are important in part because of their role in star or planet formation, it is useful to designate here certain nebulae forms which are thought to be conducive to this:

9m. molecular clouds

9b, t. Bok globules, Thackeray's globules

ZL. Galaxy clusters Though there is astronomical agreement regarding some clusters, there is controversy regarding others. In particular there has been a tendency to identify smallish clusters near the Milky Way but only very large clusters far away. It would be possible if desired to give a class number the dozen or so clusters for which there is considerable consensus.

We can identify certain types of cluster (while recognizing that the boundaries are unclear):

1. groups of galaxies

2. clusters

3. superclusters

ZG. Galaxies There is as yet no convention for designating galaxies. They are commonly referenced by location and discoverer.

1. The Milky Way. As with the Earth and Sun (below) we can privilege our own galaxy.

We can then identify certain types of galaxy:

2. spiral galaxies, disk galaxies

3. elliptical galaxies

ZC. Constellations.

There are 88 constellations utilized in modern Western astronomy (to indicate different areas of the observed sky). These include most of those recognized in Western culture, including the 12 signs of the zodiac. They could be represented with two-letter codes. Such an approach privileges Western views of the sky. An alternative approach would identify all constellations in terms first of the originating culture and then Cutter numbers.

ZX. Star clusters

There are three generally recognized types (other types can be captured synthetically). These capture the density of the cluster:

1. globular clusters, GCs

2. intermediate star clusters

3. open clusters

It may be useful to classify the observable clusters such as the Pleiades

ZY. Star systems, stellar systems A smaller number of stars that orbit each other.

2.binary stars

3. triple star systems

And so on...

ZS. Stars Stars are commonly classified by both luminosity and spectral type, though some attempts are made to combine these.

a. the Sun

There are millions of stars, some commonly designated by names, others by a combination of letters and numbers. The best approach here may be to adopt the Tycho2 catalogue (http://www.astro.ku.dk/~erik/Tycho-2/) of the 2.5 million brightest stars. Each star is coded first by a nine-digit indicator of regions in space, followed by a five digit star identifier. These 14-digit numbers could simply follow ZS.

Of course, this would require that references to stars by name be translated into these codes. An alternative is Cutter numbers. But note that stars often go by multiple names.

Some stars of particular note could be given a much shorter designation as with the Sun above.

ZS1 Luminosity: Luminosity has traditionally been indicated by roman numerals and letters. We indicate these below, but employ a more efficient lettering system:

b. white dwarfs (class VII)

c. subdwarf stars (VI)

d. dwarf stars (V)

f. subgiant stars (IV)

g. giant stars (III)

j. bright giant stars (II)

k. supergiant stars (I, often divided into subclasses a, b, and c; these can be denoted ka, kb, and kc)

h. hypergiant stars (class O)

m. Note that a variety of stars have been hypothesized but not yet observed. These may deserve careful classification. But the principle of BCC has been to classify observed objects and generally treat non-observed as creatures of particular theories.

ZS2 Spectral type: Stars are traditionally classified in order of brightness using the letters o, b, a, f, g, k, m, l, t, and y from hottest to coolest. These letters are associated with the observed color of a star:

o. Blue colored star

b. Blue white...

a. White (some blue)...

f. Yellow white...

g. Yellow (some white)

k. Orange

m. Red (some orange)

l. Red brown (scarlet)

t. Brown or magenta

y. Dark brown or black

m. As in ZS1, room should be left for hypothesized but unobserved star types.

ZB Brown dwarves. These are objects that are intermediate in size between planets and stars. Some orbit stars. There does not appear as yet to be an accepted classification of these.

ZP Planets

Since planets rotate around stars it is easiest to identify planets in terms of the stars they orbit: ZP>ZSyyy

The exception will be the planets that orbit our own Sun: ZP1:

m. Mercury

v. Venus

e. Earth

r. Mars

j. Jupiter

s. Saturn

u. Uranus

n. Neptune

x. There are also several bodies that are too small to be termed planets but are bigger than asteroids. These are often termed dwarf planets. More will likely be discovered:

xp. Pluto

xc. Ceres

xe. Eris

xh. Haumea

xm. Makemake

Planetary systems can be denoted ΣZP. We can privilege our solar system as ΣZP1. Note that planetary systems include smaller objects, such as asteroids and comets.

ZA. Asteroids. Asteroids are given a unique identifying number once their orbits are calculated. This could follow ZA (but we would then have to translate named asteroids into numbers). They are generally given provisional designations before their orbit is calculated. If these are used, translations will be necessary once the orbit is determined.

ZS: Natural satellites, moons

1. the Moon

Others will be identified with reference to the planet they orbit, followed by a Cutter number.

ZM. Comets, meteoroids, meteors, meteorites

p. Periodic comets. Over 300 of these have been numbered with a suffix P. Hundreds more are identified with a prefix P, the year discovered, and a letter and number to identify them. If we treat the suffix P as a prefix, we can have a unified system. There should be no confusion since the first set has much shorter notations. Halley's comet is thus ZMp1.

c. Non-periodic comets. (including long-period comets for which we do not yet know the orbit) These are given a designator beginning with c.

d. Lost or disappeared comets are designated with a d.

m. Meteoroids. These are fragments of comets or asteroids travelling through space.

t. Meteors and meteorites. When these fragments respectively enter our atmosphere and hit the surface.