### mass

(object's quality that determines the effects of forces and gravity)

Mass is the quality of an object that determines its gravity and also determines the degree of acceleration resulting from a force on the object. The term is also used for a measure of this quality associated with such an object. It is the quality that determines an object's weight when it is within a gravitational field, e.g., on the Earth's surface.

Mass was once considered an absolutely conserved value, but famously, the equation e=mc² adjusted that idea: mass is conserved in many "everyday" cases, but is considered a form or aspect of energy, the latter of which is conserved universally.

The above gravitational and acceleration/inertia effects are found to be proportional, suggesting they both result from the same quality. This is, in fact, tested with experiments measuring the degree to which this proportion holds, and no credible discrepancy has been found. (These two apparently-equivalent qualities are termed the inertial mass and the gravitational mass.)

Relativity has consequences regarding the meaning of the term mass. For an object at rest, the concept is straight-forward, but from a frame of reference in which the object is moving, acceleration also depends upon the speed at which it is moving, as if the moving object's mass were greater. The term rest mass is clear, and currently, it is common to treat the term mass as rest mass, and call the apparent quality of such a moving object a relativistic mass (or else avoid referring to it). At one time, that consensus wasn't as clear, so some earlier writing may treat the term mass as this relativistic mass, and the point of this is you must sometimes assure you know which is being referred to.

Mass (taken as rest mass) makes the equation e=mc² true when the object is at rest, and otherwise does not include the effects of its motion (relativistic kinetic energy). If m were to be taken as the relativistic mass, then the equation would include both its rest energy and the effects of its motion. One means of describing the impossibility of accelerating an object to the speed of light is that its relativistic mass approaches infinity as you near that speed.

The term dynamic mass refers to the mass of a body determined through dynamics, e.g., using orbital periods. This requires knowledge (at minimum) of either the distance from Earth or the mass of another object within the gravitationally-bound system.

The term point mass refers to a modeling an object's mass as being at a single point. This simplifies problems and can be a very useful approximation if distances between objects are large compared to their size and/or if an object is close to being spherically symmetric.

The term mass can be used to mean (roughly) substance, i.e., something that has mass, in phrases like mass transfer, mass loading, and coronal mass ejection.

Among the units of mass used in astrophysics:

 dalton atoms/molecules 1.66053892×10-27 kg Planck mass a "natural" unit 2.18×10-8 kg kilogram (& gram) general Moon mass moons and small planets 7.3×1022 kg .012 Earth mass (1.2%) Earth mass planets 5.972×1024 kg Jupiter mass large planets 1.898×1027 kg 318 Earth masses or .001 solar mass (0.1%) solar mass stars and larger objects 2×1030 kg 334,000 Earth masses

A mass number is a count of nucleons in a nucleus, atom or molecule, which have similar masses and is something of an approximation of the mass in daltons.

(physics,relativity,measure)
http://en.wikipedia.org/wiki/Mass
http://en.wikipedia.org/wiki/Mass_in_special_relativity

Referenced by:
accretion
accretion rate
Achernar
A-type star (A)
active galaxy
asymptotic giant branch (AGB)
active galactic nucleus (AGN)
Algol (Beta Per)
Alpha Centauri
alpha CO (αCO)
Arcturus
asteroseismology
astronomical quantities
atmosphere
atmospheric escape
AU Microscopii (AU Mic)
autoconversion rate
axion (A0)
Black Widow Pulsar (B1957+20)
Barnard's Star
barrier
barycenter
baryon
B-type star (B)
beta decay
Betelgeuse
black hole merger
black hole model
binary star
Birkhoff's theorem
black hole (BH)
Bouguer anomaly
Beta Pictoris b (β Pic b)
brown dwarf (BD)
binary SMBH (BSMBH)
bulk density
Callisto
Canopus
carbon (C)
Cassini
methane (CH4)
Chandrasekhar limit
CHEOPS
chirp mass (Mc)
conditional luminosity function (CLF)
coronal mass ejection (CME)
CNO cycle
carbon monoxide (CO)
column density
comoving units
conservation law
core accretion model
cosmological zoom simulation
critical density (ρc)
conditional stellar mass function (CSMF)
dalton (Da)
dark matter (DM)
dark matter annihilation
deuterium burning
direct collapse black hole (DCBH)
dense core mass function (DCMF)
dense core
deuterium (D)
velocity dispersion (σ)
Deep Lens Survey (DLS)
double-line spectroscopic binary
drogue chute
Earth
Eddington luminosity
ejection
electric field (E)
electron capture
electron shell
element
endothermic reaction
Epsilon Eridani
Epsilon Indi (ε Indi)
escape velocity (Ve)
Europa
Europa Clipper
event horizon (EH)
exoearth
extra-solar planet
failed binary
F-type star (F)
55 Cancri e (55 Cnc e)
final parsec problem
51 Eridani b
51 Pegasi b (51 Peg b)
free-air anomaly
free-fall time
fusion
Gaia
galaxy
galaxy bias
galaxy cluster (CL)
galaxy main sequence
galaxy merger
galaxy power spectrum
Ganymede
gas fraction
gas fraction estimation
G-type star (G)
GG Tau
giant planet
giant star
GJ 1132 b
giant molecular cloud (GMC)
gravimetry
gravitational constant
gravitational field
gravitational instability model
gravitational lensing
gravitational potential (Φ)
gravitational redshift
gravity
gravity anomaly
Great Attractor
GRO J1655-40
gravitational wave (GW)
gravitational wave background (GWB)
GW detection (GW)
gravitational-wave memory
gravitational wave spectrum
gyrochronology
halo mass function
halo abundance matching (HAM)
Hamiltonian
Hayashi track
helium (He)
helium flash
Hill stability
hypermassive neutron star (HMNS)
HR 8799
humidity
high-velocity cloud (HVC)
hydrodynamic equations
hydrogen (H)
hydrology
hydrostatic equilibrium
intracluster medium (ICM)
initial mass function (IMF)
Io
innermost stable circular orbit (ISCO)
isolation mass
J1407
J2
Jacobi integral
Jeans length
Jupiter
Kapteyn's Star
K-type star (K)
Keplerian orbit
Kelvin-Helmholtz mechanism
kilometer size barrier
Kuiper Belt (K Belt)
Lacaille 9352
Lagrangian point
Lalande 21185
Laniakea Supercluster
luminous blue variable (LBV)
Legendre polynomials
LHS 1140
libration
Large Magellanic Cloud (LMC)
Love number
low mass star
low-surface-brightness galaxy (LSB galaxy)
large scale structure (LSS)
Luyten 726-8
MACHO
main sequence star (V)
Mars
mass density
mass fraction
mass function
mass loss
mass-luminosity relation
mass ratio (μ)
mass shell
mass spectrometer
mass-to-light ratio (M/L)
Maxwell-Boltzmann distribution
M-type star (M)
mean molecular weight (μ)
mega-Earth
Mercury
metal
metallicity (Z)
meteoroid
metric
gravitational microlensing
Milky Way
minimum mass (m sin i)
mixing ratio
molecular cloud
solar mass (MSun)
MUSCLES
Neptune
neutralino
neutrino (ν)
neutron star
Navarro-Frenk-White profile (NFW profile)
NGC 3201
Nice model
neutron star merger
nuclear energy generation rate (ε)
O5 spectral class (O5)
O-type star (O)
oligarch
1.3mm observation
open cluster
Origins Space Telescope (OST)
oxygen (O)
pair production
particle spectrometer
post-common envelope binary (PCEB)
Planck constant (h)
planet
Planet Nine
planetary migration
planet demographics
planet formation
Pluto
planetary mass object (PMO)
planetary nebula (PN)
post main sequence star
Poynting-Robertson effect
precession
primary
Procyon
protostar
Proxima b
Hulse-Taylor Binary (PSR B1913+16)
Q factor
rare designator prefixes
red dwarf
red giant
reduced mass
relativistic energy
relativistic invariance
relativistic momentum
red-giant branch (RGB)
RHAPSODY
Rigel
Roche limit
Rosetta
Ross 154
Ross 248
rotation curve
Saha equation
Saturn
Schönberg-Chandrasekhar limit
Scholz's Star
Spitzer Extended Deep Survey (SEDS)
star formation rate (SFR)
star-formation rate stellar-mass ratio
Spitzer HETDEX Exploratory Large Area Survey (SHELA)
Sirius
superluminous supernova (SLSN)
supermassive black hole (SMBH)
solar wind
specific angular momentum (J)
specific volume
spectral class
spectrometer
spectrometry
spicule
spiral galaxy
standard gravitational parameter (μ)
star formation (SF)
stellar birth rate function
stellar demographics
stellar distance determination
stellar evolution
stellar mass determination
stellar parameter determination
stellar structure
stellar wind
strong-field gravity
subgiant
substellar object
Sun
super-Earth
supergiant
surface density (Σ)
surface gravity
symbiotic binary
synchronous orbit
Tully-Fisher relation (TFR)
Thomson scattering
tidal force
tidal tail
timescale (t)
Titan
21cm line
Tolman-Oppenheimer-Volkoff limit (TOV)
TRAPPIST-1
Triangulum II (Tri II)
Triton
T Tauri
transit timing variations (TTV)
turn-off point (TO)
TW Hydrae (TW Hya)
ultraluminous X-ray source (ULX)
Uranus
variable star
Vega
Venus
VLT-FLAMES Tarantula Survey (VFTS)
virial parameter
virial theorem
Vogt-Russell theorem
water-ice planet
weak lensing (WL)
white dwarf
WIMP
WISE 0855-0714
Wolf 359
Wolf-Rayet galaxy
wormhole
CO to H2 factor (Xco)

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