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 the obvious target for the closest study galaxies, especially disk galaxies. A stellar population classification based upon metallicity measures and location consists of 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 as presumed to grow with succeeding generations of stars, the metals being formed by stellar fusion and supernovae and spread by the latter and stellar wind, so older stars, necessarily leftovers from earlier generations have lower metallicity. The Sun has a high metallicity but not the highest, in the middle of the thin disk's range. Stellar associations, the leftovers from recent star formation, can have higher.

(galaxy,Local Group,local)

Referenced by:
anomalous microwave emission (AME)
astronomical quantities
blind survey
Canis Major Dwarf Galaxy
carbon (C)
cosmic optical background (COB)
cosmic distance ladder
cosmic dust
Council of Giants
cosmic X-ray background (CXB)
data cube
diffuse emission
disk galaxy
dwarf galaxy
Event Horizon Telescope (EHT)
field galaxy
foreground subtraction
frame of reference
fast radio burst (FRB)
galactic binary
galactic bulge
galactic center
galactic electron density
galactic halo
galactic north
galactic plane
galaxy group
galaxy main sequence
Galactic All-sky Survey (GASS)
Green Bank Telescope (GBT)
G-dwarf problem
globular cluster (GC)
Atlas of Galactic Nebulae (GN)
Gould's Belt
great debate
Hα survey
hierarchical assembly of galaxies
high-velocity star
hot DOG
Hubble constant (H0)
Hubble Ultra-Deep Field (HUDF)
high-velocity cloud (HVC)
hypervelocity star (HVS)
IC 342
intensity mapping
interstellar magnetic field (ISMF)
jansky (Jy)
Kapteyn universe
kinematic distance
Laniakea Supercluster
Large Magellanic Cloud (LMC)
Local Group (LG)
Local Sheet
Lockman hole
local standard of rest (LSR)
luminosity density
luminosity distance (dL)
Local Volume (LV)
Andromeda (M31)
Triangulum Galaxy (M33)
MACHO Project
metallicity (Z)
solar mass (MSun)
multiplicity fraction
Milky Way chemical evolution
N-body problem
NASA/IPAC Extragalactic Database (NED)
Omega Centauri
Oort constants
open cluster
oxygen (O)
red dwarf
rotation curve
RR Lyrae variable
Sagittarius Dwarf Elliptical Galaxy (Sgr dE)
satellite galaxy
Schwarzschild radius
Scutum-Centaurus Arm
Sloan Digital Sky Survey (SDSS)
supermassive black hole (SMBH)
Small Magellanic Cloud (SMC)
Smith Cloud
solar apex
Soltan argument
spectral line
spiral arm
spiral galaxy
Spitzer Space Telescope (SST)
starburst galaxy
stellar association
stellar distance determination
stellar population
21cm line
Triangulum II (Tri II)
Two Micron All-sky Survey (2MASS)
ultra-faint dwarf galaxy (UFD)
velocity-metallicity relation
Virgo Cluster
Westerhout Radio Survey (W)
Wolf-Rayet star
X-ray luminosity function (XLF)
zone of avoidance (ZOA)