Astrophysics (Index)About

Milky Way

(our galaxy)

The Milky Way is a spiral galaxy in which we reside and appears in the night sky as a glowing band. The galaxy is on the order of 100,000 light-years in diameter, about 1000 light-years in thickness and has 200-400 billion stars. Its mass is about a trillion solar masses. The solar system is about half way between its center and its edge. It is the second largest galaxy in the Local Group, the largest being Andromeda. An orbit of the Sun around the galaxy lasts in the range of 225-250 million years (i.e., the galactic period aka galactic year or cosmic year). The Milky Way's oldest stars are about 13 billion years old.

The Milky Way is naturally a target for up-close study of a galaxy, specifically, a disk galaxy. A stellar population classification of Milky Way stars based upon metallicity measures and location divides them into Population I stars, in the bulge and globular clusters with low metallicity, and Population II stars in the disk and spiral arms with higher metallicity. Of the latter group, location, kinematics and metallicity distinguish a thick disk at the lower end of the Population II metallicity scale and a thin disk at the higher end. Metallicity is presumed to grow with succeeding generations of stars, the metals being formed by stellar fusion and supernovae, the metals spread by the latter and by stellar wind, so older stars, necessarily leftovers from earlier generations, have lower metallicity. The Sun has a high metallicity but not the highest, falling in the middle of the thin disk's range. Stellar associations, the leftovers from recent star formation, can have higher.

(galaxy,Local Group,local)
Further reading:

Referenced by pages:
anomalous microwave emission (AME)
astronomical quantities
blind survey
Canis Major Dwarf Galaxy
carbon (C)
cosmic background radiation (CBR)
CMB anisotropies
cosmic optical background (COB)
cosmic distance ladder
cosmic dust
cosmic rays (CR)
Council of Giants
cosmic X-ray background (CXB)
dark matter halo
data cube
diffuse emission
disk galaxy
dispersion measure (DM)
distance modulus (μ)
dwarf galaxy
Event Horizon Telescope (EHT)
extragalactic astronomy
field galaxy
foreground subtraction
frame of reference
fast radio burst (FRB)
galactic astronomy
galactic binary
galactic bulge
galactic center
galactic electron density
galactic halo
galactic north
galactic plane
galaxy age determination
galaxy cluster (CL)
galaxy group
galaxy main sequence
Galactic All-sky Survey (GASS)
Green Bank Telescope (GBT)
G-dwarf problem
giant elliptical galaxy
globular cluster (GC)
Atlas of Galactic Nebulae (GN)
Galactic O Star Catalog (GOSC)
Gould's Belt
great debate
Hα survey
hierarchical assembly of galaxies
high-velocity star
hot DOG
Hubble Ultra-Deep Field (HUDF)
high-velocity cloud (HVC)
hypervelocity star (HVS)
IC 342
intensity mapping
intergalactic dust
interstellar magnetic field (ISMF)
jansky (Jy)
Kapteyn universe
kinematic distance
Laniakea Supercluster
luminous blue variable (LBV)
Large Magellanic Cloud (LMC)
Local Bubble
Local Group (LG)
Local Sheet
Lockman hole
Case-Hamburg Survey (LS)
local standard of rest (LSR)
luminosity density
luminosity distance (dL)
Local Volume (LV)
Andromeda (M31)
Triangulum Galaxy (M33)
MACHO Project
Magellanic clouds (MC)
Magellanic Stream
magnetic field
metallicity (Z)
Milky Way subgroup
Monoceros Ring
solar mass (MSun)
multiplicity fraction
Milky Way chemical evolution
N-body problem
NASA/IPAC Extragalactic Database (NED)
neutrino (ν)
nova (N)
Omega Centauri
Oort constants
open cluster (OC)
oxygen (O)
primordial gravitational waves
radial velocity (RV)
red dwarf
rotation curve
rotating radio transient (RRAT)
RR Lyrae variable (RRL)
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
satellite galaxy
satellite plane problem
Schwarzschild radius
Scutum-Centaurus Arm
Sloan Digital Sky Survey (SDSS)
SGR J1745-2900
supermassive black hole (SMBH)
Small Magellanic Cloud (SMC)
Smith Cloud
solar apex
solar neighborhood
Soltan argument
spectral line
spinning dust emission
spiral arm
spiral galaxy
Spitzer Space Telescope (SST)
starburst galaxy
stellar association
stellar-mass black hole
stellar distance determination
stellar kinematics
stellar population
stellar stream
thermal dust emission
21-cm line
Triangulum II (Tri II)
Two Micron All-sky Survey (2MASS)
ultra-faint dwarf galaxy (UFD)
velocity-metallicity relation
Virgo Cluster
Virgo Stellar Stream
Westerhout Radio Survey (W)
Wolf-Rayet star
X-ray luminosity function (XLF)
zone of avoidance (ZOA)