The age of the Galaxy is currently estimated to be about 13.6 billion (109) years, which is nearly as old as the Universe itself.
This estimate is based upon research performed in 2004 by a team of astronomers: Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton. The
team used the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure, for the first time, the beryllium content of two stars in globular cluster NGC 6397. This allowed them to deduce the elapsed time between the rise of the first generation of stars in the entire Galaxy and
the first generation of stars in the cluster, at 200 million to 300 million years. By including the estimated age of the stars in the globular cluster (13.4 ± 0.8 billion years), they estimated the age of
the Galaxy at 13.6 ± 0.8 billion years.
Observed structure of the Milky Way's spiral arms
As of 2005, the Milky Way is thought to comprise a large barred spiral galaxy of Hubble type SBbc (loosely wound barred spiral) with a total mass of about 1012 solar masses (M☉), comprising 200-400 billion stars .
It was only in the 1980s that astronomers began to suspect that the Milky Way is a barred spiral rather than an ordinary spiral, which observations in 2005 with the Spitzer Space Telescope have since confirmed, showing that the galaxy's central bar is larger than previously suspected .
The galactic disk has an estimated diameter of about 100,000 light-years (see 1 E20 m for a list of comparable distances). The distance from the Sun to the galactic center is estimated at about 26,000 light-years. The disk bulges outward at the center.
The galactic center harbours a compact object of very large mass, strongly suspected to be a supermassive black hole; this object is associated with the Sagittarius A* radio source. Most galaxies are believed to have a supermassive black hole at their center.
As is typical for many galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars
in the galaxy does not depend strongly on its distance from the center. Away from the central bulge or outer rim, the typical
stellar velocity is between 210 and 240 km/s . Hence the orbital period of the typical star is directly proportional only to the length of the path travelled. This is
unlike in the solar system where different orbits are also expected to have significantly different velocities associated with them.
The galaxy's bar is thought to be about 27,000 light years long, running through the center of the galaxy at a 44±10 degree
angle to the line between our sun and the center of the galaxy. It is composed primarily of red stars, believed to be ancient.
Observed and extrapolated structure of the spiral arms
Each spiral arm describes a logarithmic spiral (as do the arms of all spiral galaxies) with a pitch of approximately 12 degrees. There are believed to be four major spiral
arms which all start at the Galaxy's center. These are named as follows, according to the image at right:
There are at least two smaller arms or spurs, including:
- 11 - Orion Arm (which contains the solar system and the Sun - 12)
Outside of the major spiral arms is the Outer Ring or Monoceros Ring, a ring of stars around the Milky Way proposed by astronomers Brian Yanny and Heidi Jo Newberg, which consists of gas and stars torn from other galaxies billions of years ago.
The galactic disk is surrounded by a spheroid halo of old stars and globular clusters. While the disk contains gas and dust obscuring the view in some wavelengths, the halo does not. Active star formation takes place in the disk (especially in the spiral arms, which represent areas of high density), but not in the
halo. Open clusters also occur primarily in the disk.
Recent new discoveries have given added dimension to our knowledge of the structure of the Milky Way. With the discovery
that the disc of the Andromeda Galaxy (M31) extends much further than previously thought , the possibility of the disk of the Milky Way extending further is a clear possibility and is supported by evidence of the
newly discovered Outer Arm extention of the Cygnus Arm. With the discovery of the Sagittarius Dwarf Elliptical Galaxy  came the discovery of a ribbon of galactic debris as the polar orbit of Sagittarius and its interaction with the Milky Way
tears it apart. Similarly, with the discover of the Canis Major Dwarf Galaxy , a ring of galactic debris from its interaction with the Milky Way encircles the galactic disk.
The Sun's place in the Milky Way
The Sun (and therefore the Earth and Solar System) may be found close to the inner rim of the Orion Arm, in the Local Fluff, at the generally accepted distance of 8.0±0.5 kpc (Reid, M. J. 1993, Annu. Rev. Astron. Astrophys., 31, 345) from the galactic center. The distance between the local arm and the next arm out, the Perseus Arm, is about 6,500 light-years (see ).
The Apex of the Sun's Way, or the solar apex, refers to the direction that the Sun travels through space in the Milky Way. The general direction of the sun's galactic
motion is towards the star Vega near the constellation of Hercules, at an angle of roughly 86 degrees to the direction of the galactic center. The sun's orbit around the galaxy is expected
to be roughly elliptical with the addition of perturbations due to the galactic spiral arms and non-uniform mass distributions.
We are presently about 8.0 kpc from the center of the galaxy and roughly 1/8 of an orbit before perigalacton (the sun's closest approach to the center).
It would take the solar system about 225-250 million years  to complete one orbit ("galactic year"), and so is thought to have completed about 20-25 orbits during its lifetime. The
orbital speed is 217 km/s, i.e. 1 light-year in ca. 1400 years, and 1 AU in 8 days.
The Sun's place in the Milky Way is crucial to various galactic calculations. Measurements to the center of the Milky Way
have varied greatly from 8.5±0.5 kpc to 7.9±0.2 kpc (one of the most recent measurements in 2005) . The Hayden Planetarium  uses 8.0 kpc in their interactive 3D Milky Way Atlas, a figure that falls within virtually all data ranges.
The galactic neighborhood
The Milky Way, the Andromeda Galaxy and the Triangulum Galaxy are the major members of the Local Group, a group of some 35 closely bound galaxies; The Local Group is part of the Virgo Supercluster.
The Milky Way is orbited by a number of dwarf galaxies in the Local Group. The largest of these is the Large Magellanic Cloud with a diameter of 20,000 light years. The smallest, Carina Dwarf, Draco Dwarf, and Leo II Dwarf are only 500 light years in diameter. The other dwarfs orbiting our galaxy are the Small Magellanic Cloud; Canis Major Dwarf, the closest; Sagittarius Dwarf Elliptical Galaxy, previously thought to be the closest; Ursa Minor Dwarf; Sculptor Dwarf, Sextans Dwarf, Fornax Dwarf, and Leo I Dwarf.
In January 2006, researchers reported that the heretofore unexplained warp in the disk of the Milky Way has now been mapped
and found to be a ripple or vibration set up by the Large and Small Magellanic Clouds as they circle the Milky Way, causing
vibrations at certain frequencies when they pass through the edges of our Galaxy. Previously, these two galaxies, at around
2% of the mass of the Milky Way, were considered too small to influence the Milky Way. However, by taking into account dark matter, the movement of these two galaxies creates a wake that influences the larger Milky Way. Taking dark matter into account
results in an approximately twenty fold increase in mass for the Milky Way. This calculation is according to a computer model
made by Martin Weinberg of the University of Massachusetts, Amherst. In this model, the dark matter is spreading out from the Milky Way disk with the known gas layer. As a result, the model
predicts that the gravitational impact of the Magellanic Clouds is amplified as they pass through the Milky Way.
Speed through space
In the general sense, the absolute speed of any object through space is not a meaningful question according to Einstein's Special Theory of Relativity, which declares that there is no "preferred" inertial frame of reference in space to compare the galaxy's motion with. (Motion must always be specified with respect to another object.)
With this in mind, many astronomers believe the galaxy is moving through space at approximately 600km per second relative
to the observed locations of other nearby galaxies. Most recent estimates range from 130km/second to 1,000km/second. If indeed
the Milky Way is moving at 600km per second, we are travelling 51.84 million km per day or more than 18.9 billion km per year.
For comparison, this would mean that each year, we are travelling about 4.5 times the distance that Pluto lies from the earth (at its closest). The Milky Way is thought to be moving in the direction of the constellation Hydra.
- Main article: Milky Way (mythology)
There are many creation myths around the world regarding the Milky Way. In particular, there are two similar ancient Greek stories that explain the etymology
of the name Galaxias (Γαλαξίας) and its association with milk (γάλα).
Some myths associate the constellation with a herd of cattle whose milk gives the sky its blue glow. In Eastern Asia, people
believed that the hazy band of stars was the "Silvery River" of Heaven. This is written in Kanji as 銀河.
Akashaganga is the Indian name for the milky way galaxy, which means Ganges River of the Sky.
According to Greek mythology, the Milky Way was formed by Hera, who spilled milk in the sky after discovering that Zeus had tricked her into feeding young Heracles. In another vairance, Hermes snuck Hercules into Olympus to drink from the breasts of Hera who was asleep. Heracles bit Hera's nipple shooting her milk into the skies forming the Milky Way.
Future of Milky Way
Current measurements suggest the Andromeda Galaxy is approaching us at 300 kilometres per second, and that the Milky Way may collide with it in several (3-4) billion years.
If they do collide, it is thought that our sun and other stars will probably not collide with other stars, but merge to form
an elliptical-shaped galaxy over the course of about a billion years.
On January 9, 2006 Mario Juric and others of Princeton University announced that the Sloan Digital Sky Survey of the northern sky has found a huge and diffuse structure (spread out across an area around 5,000 times the size of a full
moon) within the Milky Way that does not seem to fit within our current models. The collection of stars rises close to perpendicular
to the plane of the spiral arms of the Milky Way. The proposed likely interpretation is that a dwarf galaxy is merging with the Milky Way. This galaxy is tenatively named the Virgo Stellar Stream and is found in the direction of Virgo about 30,000 light years away.