Astrophysics (index)

Hydrogen

(H)
(most prominent element, atomic number 1.)

Hydrogen (symbol H) is the element with atomic number 1. It is the most prominent element in the universe, 75% by mass, more than 90% by number of atoms.

Neutral atomic hydrogen is termed HI, and a cloud of it is known as an HI Region (HI). A region with excited and ionized atomic hydrogen (HII) is termed an HII Region (HII).

Hydrogen forms molecules of two hydrogen atoms (HH, H2, or H2), which produces very little Electromagnetic Radiation (EMR). These are presumed to form mostly on the surface of Cosmic Dust particles in the Interstellar Medium (ISM). Clouds of it are termed Molecular Clouds, which also carry tiny amounts of other compounds such as Carbon Monoxide (CO), which are, in turn, useful in identifying such clouds and with the use of the CO to H2 Factor (Xco), estimating their mass.

The Spectral Lines of hydrogen are often used in astronomical observation. They are classified by series, each consisting on photons generated by the relaxation of electrons from more excited energy state to a specific lower energy state or orbit, the states being numbered as n=1,2,3,... Among the series:

There are also spectral lines from smaller transitions, e.g., the 21cm Line.


(element,non-metal,chemistry)
http://en.wikipedia.org/wiki/Hydrogen

Referenced by:
Abundances
A-Type Star (A)
Asymptotic Giant Branch (AGB)
Alpha CO (αCO)
Amine
Astronomical Quantities
Atmosphere
Atomic Excitation
Balmer Jump
Balmer Series
Baryon Acoustic Oscillations (BAO)
B-Type Star (B)
Be Star
Binding Energy
Biosignature
Bohr Model
Brackett Series
Carbonate System
Methylidyne (CH)
Methane (CH4)
Canadian Hydrogen Intensity Mapping Experiment (CHIME)
Cosmic Microwave Background (CMB)
CNO Cycle
Carbon Monoxide (CO)
COLD GASS
Core Collapse Supernova
Critical Density
Dark Age
Degeneracy
Dendrogram
Dense Core
Deuterium (D)
Energetic Neutral Atom (ENA)
Epoch of Reionization (EOR)
Escape Fraction
Ethylene (C2H4)
F-Type Star (F)
Fine Structure
Gas Flow
Gas Giant
Galactic All-Sky Survey (GASS)
G-Type Star (G)
Giant Planet
Giant Molecular Cloud (GMC)
Gunn-Peterson Trough
H-alpha (Ha)
Horizontal Branch (HB)
Acetylene (C2H2)
Helium (He)
Helium Runaway Shell
HERA
HII Region (HII)
HI Region (HI)
Hydrocarbon (HC)
Hyperfine Structure
Ice
Ice Giant
Intracluster Medium (ICM)
Intergalactic Medium (IGM)
Iron (Fe)
K-Type Star (K)
Lyman-Break Galaxy (LBG)
L-Type Star (L)
Lithium (Li)
Low-Frequency Array (LOFAR)
Lyman Alpha (Ly-α)
Lyman-Alpha Forest
Lyman Series
Lyman-Werner Photon
Main Sequence Star
M-Type Star (M)
Metal
Metallicity (Z)
Metastable
Molecular Cloud
Murchison Widefield Array (MWA)
Ammonia (NH3)
Nitrogen (N)
Nova
Nucleosynthesis
O5 Spectral Class (O5)
O-Type Star (O)
Polycyclic Aromatic Hydrocarbon (PAH)
Paschen Series
Acidity (pH)
Photoionization
Pre-Main-Sequence Star (PMS)
Proton-Proton Chain
Protogalaxy
Recombination
Red Giant
Reducing Atmosphere
Star Formation Rate (SFR)
Supernova (SN)
Spectral Class
Spectral Line
State of Ionization
Stellar Age Determination
Subgiant
Sun
Titan
21cm Experiment
21cm Line
T-Tauri Star (TTS)
CO to H2 Factor (Xco)

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