- standard gravitational parameter (μ) - a body's mass times the universal gravitational constant
- sigma-8 tension (S8 tension) - Lambda CDM anomaly regarding matter fluctuation
- Paschen series - hydrogen lines for electrons settling from n > 3 to n = 3
- alpha process (α process) - synthesis of elements through alpha capture
- M-type star (M) - spectral class of star with a temperature in the vicinity of 2500 K
- Brackett series - hydrogen lines for electrons settling from n > 4 to n = 4
- Hill radius - radius of gravitational influence of a body
- Fermi sea - atom's minimal-energy electrons filling its lower shells
- astronomical symbol - traditional symbols specific to astronomy, for Sun, Earth, etc.
- J2 - geopotential coefficient regarding a planet's oblateness
- Rayleigh-Jeans law - yields approximation of black-body curve useful at low frequencies
- Hellings and Downs curve - expected correlation in pulsar timing residuals from random waves
- Bethe-Heitler process - type of pair production interaction near nuclei
- BPT diagram - diagram comparing emission-line ratios for characterizing ionization
- neutron degenerate matter - matter made up primarily of neutrons
- final parsec problem - lack of a convincing theory on how SMBHs can reach each other
- dex - a number or ratio's log base 10
- wCDM - Big-Bang cosmological model with constant cosmological equation of state
- u-v plane - plane for displaying Fourier transforms of signal from the sky
- e-folding time - time to increase by a factor of e
- equilibrium temperature (Teq) - temperature a planet would have if it were an externally-heated black body
- ugriz photometric system - photometric system used for SDSS
- Tolman-Oppenheimer-Volkoff limit (TOV) - maximum mass of a neutron star
- dispersion measure (DM) - to what degree an EMR signal's lower frequencies are delayed
- Lyman break (LB) - abrupt change in galaxy spectrum at the Lyman series wavelength limit
- Gamow peak - relative speed most likely to cause atoms to fuse within a gas
- analytical methods - using solved equations rather than a lot of arithmetic
- Balmer jump (BJ) - abrupt change in stellar spectrum at the Balmer series wavelength limit
- radiation era - early universe era when radiation pressure dominated
- Rosseland mean opacity - a useful weighted average of opacities at all the frequencies
- astronomical catalog - list of observed astronomical bodies including characteristics
- epoch J2000.0 - noon 1/1/2000 GMT as used as a time reference
- solar mass (MSun) - mass unit representing the mass of the Sun
- Jeans length - critical radius above which gravity will collapse a cloud
- Korsch telescope - type of three-mirror reflector telescope
- arcsecond (arcsec) - a 3600th of an angular degree
- Balmer series (H) - hydrogen lines for electrons settling from n > 2 to n = 2
- star formation rate (SFR) - rate at which material such as gas is turned into stars
- Bondi radius - radius within which a body moving through a medium will draw it in
- Toomre Q parameter (Q) - stability criterion for differentially rotating disks
- electron degeneracy - electrons set free of atoms by the Pauli exclusion principle
- broad line region (BLR) - AGN region producing broader lines
- Rydberg unit - unit of energy near 13.6 eV
- gravitational wave strain (h) - a measure of the magnitude of a gravitational wave
- Alcock-Paczyński effect (AP effect) - type of distortion of the apparent depth of galaxy clusters
- halo orbit - type of orbit around an unstable Lagrangian point
- Mach number - ratio of flow-speed to sound-speed
- relativistic speed - a substantial fraction of the speed of light
- Salpeter timescale - timescale for black hole growth
- optical depth (τ) - a measure of opaqueness of a path of light
- K-type star (K) - spectral class of star a bit cooler than the Sun
- Balmer-break galaxy (BBG) - a galaxy emitting very little shorter than 3646 angstroms
- CO ladder - series of CO rotational spectral lines
- wavefront error (WFE) - measure of a class of telescope distortion
- Lick indices - defined set of spectral line indexes for stars
- Lambda-CDM model (ΛCDM) - Big-Bang cosmological model with a cosmological constant and cold dark matter
- plate scale - relation between angle and distance across an image
- alpha-enhanced - metallicity with a high percentage of alpha elements
- SH0ES - survey to increase the accuracy of the cosmic distance ladder
- line shape function - function describing the shape of a spectral line
- number density (n) - number of objects per volume
- relativistic invariance - quantity that remains the same regardless of frame of reference
- Eddington bias - selection bias from mistaking something common for something rare
- LDN 1527 (L1527) - dark nebula in Taurus
- angular power spectrum - method of characterizing the CMB
- main sequence fitting - cluster star distance determined through fitting with the H-R diagram
- surface of last scattering - sphere around us from which CMB photons are just reaching us
- International Celestial Reference System (ICRS) - standardized variation of equatorial coordinate system
- kappa mechanism (κ-mechanism) - stellar instability caused by opacity increasing with temperature
- tremendously low frequency (TLF) - presumably electromagnetic radiation, frequency below 3 Hz
- Pfund series - hydrogen lines for electrons settling from n > 5 to n = 5
- bolometric luminosity (LBol) - total luminosity of an object at all wavelengths
- galaxy main sequence - relation between galaxies' star formation and stellar mass
- PHOENIX stellar model - computer model of a stellar photosphere
- Kelvin-Helmholtz timescale (KH timescale) - time that would radiate away a body's heat energy given its luminosity
- spaxel - like an image-pixel but with a SED for the location
- gravitationally bound - description of objects kept together by gravity
- column density - measure of the matter through which EMR is passing
- line blanketing - so many bunched spectral lines that they cannot be distinguished
- Lyman series (L) - hydrogen series from electrons settling from n > 1 to n = 1
- specific intensity - intensity per unit wavelength or frequency
- carbon monoxide (CO) - compound of carbon and oxygen, one atom each
- Limber approximation - formula approximating the density of galaxies in some direction
- ionization fraction - a substance's ratio of unattached electrons to nuclei
- Strömgren sphere - sphere of ionized hydrogen around an OB star
- double-line spectroscopic binary (SB2) - spectroscopic binary star where a specific line shows up at two different wavelengths
- spectral type - classification of stars based upon spectral features
- transient astronomy - study of short-term astronomical phenomena
- metallicity (Z) - metal fraction of an object
- gray body - ideal object that reflects the same fraction of light at any wavelength
- Fisher information - measure of the information provided by experimental data
- gigayear (Gy) - a billion years
- astronomical object - planet, star, galaxy, etc.
- chirp mass (Mc) - a reduced-mass-like quantity that relates to gravitational waves
- proto-cluster - newly-formed galaxy cluster
- Lyot coronagraph (CLC) - original coronagraph design
- redshift (z) - change to longer wavelengths due to Doppler effects
- Hayashi track - H-R diagram track of evolution of some pre-main-sequence stars
- moment of inertia factor - characterization of mass distribution within a planet
- electron pressure - the electron contribution to pressure within a plasma
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