Nebula

A Nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases.

• Nebulae or nebulas can affect ship sensor suites or other ship equipment.
• They are Astrographic Features.

Description (Specifications)

Interstellar clouds are regions of gas, dust, and plasma that have a higher average density than the general interstellar medium. They are typically composed of about 70% hydrogen, the bulk of the remainder being helium with traces of other elements. Nebula can range in size from as small as 1 pc in diameter, as in the case of planetary nebulae, to over 100 pc wide in the case of some of the largest nebular clouds.

Basic Nebula Types

Interstellar clouds can be classified into 3 general types based on the primary form of hydrogen found within:

1. Neutral Clouds (H I regions - formed of atomic hydrogen)
2. Ionized Clouds (H II regions - formed of positively-ionized hydrogen [i.e. "Plasma"])
3. Molecular Clouds (Molecular Hydrogen - formed of H₂)

Hydrostatic Equilibrium

Under normal circumstances interstellar clouds exist in a state of hydrostatic equilibrium, in which the natural self-gravitation that would otherwise cause the cloud to collapse is balanced by the outward pressure within the cloud due to motion of the atoms and molecules that compose it. Star formation is normally caused within molecular clouds by a triggering event which locally disturbs this equilibrium, causing runaway local collapsing regions within the cloud. Such causes can be the collision of one cloud with another, or the shock-wave within the interstellar medium caused by a nearby supernova explosion.

Selected Nebulae

• Anellet Cloud
• Anundarluu, The
• Anterior Cloud
• Basilisk Nebula
• Beta Niobe Nebula
• Block Nebula
• Bourne Cloud
• The Cauldron
• Celella Nebula
• Coalsack Nebula
• Curtain Nebula
• Curtain Nebula, Lesser
• Dark Cloud
• Deimos Cloud
• Demon's Eye Nebula
• Destiabr Nebula
• Helix Nebula
• Holowon Cloud
• Hook Nebula
• Horsehead Nebula
• Magister Cloud
• Inferno Nebula
• Orion Nebula
• North American Nebula
• Pelican Nebula
• Phobos Cloud
• Rim Reach Nebula
• Shell Nebula, Greater
• Shell Nebula, Lesser
• Separe Cloud
• Shadow Cloud
• Spark Nebula
• Ulund Cloud, Great
• Ulund Cloud, Little
• Veil of The Rim
• Verant's Head Nebula
• Wisp Cloud

History & Background (Dossier)

Ancient Solomani astronomers originally used the Latin term "Nebula" (Lat. "Cloud") to refer to any diffuse object observed in the night skies of Ancient Terra. These included what were termed "nebulous stars" at the time (which included both what were later discovered to be star clusters and nebulae proper) as well as what were later discovered to be galaxies before their true nature was known. Numerous astronomical catalogs were published by different Terran observers over a long span of time, which included among their lists objects originally classified as "nebulae". Such catalogs included the Messier Catalog of Charles Messier (abbr. "M", which was later supplemented by the the Caldwell Catalog (abbr. "C")), and the New General Catalog of Nebulae and Clusters of Stars (abbr. "NGC"), with the "Index Catalog of Nebulae and Clusters of Stars" (abbr. "IC") as an associated later supplement, among others.

• Known to Vilani science

Nebula Effects on Ships

Nebulae often interfere with sensors, especially commercial ship sensor suites. They can affect other ship equipment as well. Sufficient study by astronomers will allow jumping into and out of the better known nebulae. There is still enough clutter that an astrogator has to aim for the destination's outer reaches. Misjumps are a strong possibility under many to most conditions.

Old Spacer's Comments: A nebula is quite impressive from a distance, but usually doesn't look like much close-up. The gas and dust in the typical nebula are actually very sparse, barely more dense than a pure vacuum. They look impressive from a distance only because they're so deep along our line of sight. Many spacers have reported that fuel skimming from a nebula would be about as effective as collecting water by running through fog with a bucket. Under most conditions, it would degrade sensors beyond a few dozen AU. NAFAL (>0.1c) travel would be hazardous; but it wouldn't ordinarily affect jump nor could it be efficiently skimmed without something like a electro-magnetic ramscoop.

• Note that the term dust does not generally refer to free-floating silicates or tiny flakes of rock – it is an astronomical term meaning any element that isn't either hydrogen or helium. In the case of nebulae, molecules of elements such as nitrogen or oxygen are dust.

Nebula Size & Relative Location

Nebulae are typically measured in the following units:

Nebula Size & Relative Location
Size	Typical Metrics	Remarks
Astrographic Hex	Parsec or AU	These smaller nebulae are typically represented on a single astrographic hex.
Subsector	Light-year or Deshi	They are smaller nebulae by astronomic standards, but less than a subsector in size.
Sector	Light-year or Deshi	These are typical nebulae, often several subsectors in size. Some might be proto-galaxies, failed galaxies, or accreted star clusters... possibly the remants of a nova starburst.
Multi-Sector	Light-year or Deshi	These are truly massive nebulae, often several sectors in size.

References & Contributors (Sources)

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This list of sources was used by the Traveller Wiki Editorial Team and individual contributors to compose this article. Copyrighted material is used under license from Far Future Enterprises or by permission of the author. The page history lists all of the contributions.

• Traveller Wiki Editorial Team
• Author & Contributor: WHULorigan
• Author & Contributor: Lord (Marquis) and Master of Sophontology Maksim-Smelchak of the Ministry of Science