The Milky Way Galaxy belongs to the Local Group, a smaller group of 3 large and over 30 small galaxies, and is the second largest (after the Andromeda Galaxy M31) but perhaps the most massive member of this group. M31, at about 2.9 million light years, is the nearest large galaxy, but a number of faint galaxies are much closer: Many of the dwarf Local Group members are satellites or companions of the Milky Way. The two closest neighbors, both already mentioned, have only recently been discovered: The nearest of all, discovered in 2003, is an already almost disrupted dwarf galaxy, the Canis Major Dwarf, the nucleus of which is about 25,000 light-years away from us and about 45,000 light-years from the Galactic Center. Second comes SagDEG at about 88,000 light years from us and some 50,000 light years from the Galactic Center. These two dwarfs are currently in close encounters with our Galaxy and in sections of their orbits situated well within the volume ocupied by our Milky Way. They are followed in distance by the more conspicuous Large and Small Magellanic Cloud, at 179,000 and 210,000 light years, respectively.

The spiral arms of our Milky Way contain interstellar matter, diffuse nebulae, and young stars and open star clusters emerging from this matter. On the other hand, the bulge component consists of old stars and contains the globular star clusters; our galaxy has probably about 200 globulars, of which we know about 150. These globular clusters are strongly concentrated toward the Galactic Center: From their apparent distribution in the sky, Harlow Shapley has concluded that this center of the Milky Way lies at a considerable distance (which he overestimated by factors) in the direction of Sagittarius and not rather close to us, as had been thought previously.

Our solar system is thus situated within the outer regions of this galaxy, well within the disk and only about 20 light years "above" the equatorial symmetry plane (to the direction of the Galactic North Pole, see below), but about 28,000 light years from the Galactic Center. Therefore, the Milky Way shows up as luminous band spanning all around the sky along this symmetry plane, which is also called the "Galactic Equator". Its center lies in the direction of the constellation Sagittarius, but very close to the border of both neighbor constellations Scorpius and Ophiuchus. The distance of 28,000 light years has recently (1997) been confirmed by the data of ESA's astrometric satellite Hipparcos. Other investigations published consequently have disputed this value and propose a smaller value of some 25,000 light years, based on stellar dynamics; a recent investigation (McNamara et.al 2000, based on RR Lyrae variables) yields roughly 26,000 light years. These data, if of significance, wouldn't immediately effect values for distances of particular objects in the Milky Way or beyond.

The solar system is situated within a smaller spiral arm, called the Local or Orion Arm, which is merely connection between the inner and outer next more massive arms, the Sagittarius Arm and the Perseus Arm; see our Milky Way Spiral Structure page.

Similar to other galaxies, there occur supernovae in the Milky Way at irregular intervals of time. If they are not too heavily obscurred by interstellar matter, they can be, and have been seen as spectacular events from Earth. Unfortunately, none has yet appeared since the invention of the telescope (the last well observed supernova was studied by Johannes Kepler in 1604).

Milky Way pictures are wide-field exposures. Besides being attractive and often colorful, they are often suited to view the Milky Way objects (including nebulae and star clusters) in their celestial surroundings of field stars. Some fields include lots of Messier objects and thus included here:

• Milky Way central region including constellations Sagittarius, Scorpius, Ophiuchus and Scutum, and map of the Milky Way Central Region, by Bill Keel of the University of Alabama
• Milky Way in Sagittarius, including portions of Scorpius and Ophiuchus
• Milky Way around M17, M18, and M24

In order to obtain a picture of the whole Milky Way as it appears from Earth, one must either compose a mosaic of many photographs (optionally computer-processed), or create a drawing; fine examples may be accessed below:

• A good Milky Way photo mosaic
• Knut Lundmark's drawing of the Milky Way

In the infrared light, the structure of the Milky Way can be better investigated, as the obscurring dust clouds are of better transparency for long wavelength IR than for the visible light. The Cobe satellite has provided an infrared image of the Milky Way's central region.

The central region of the Milky Way, as those of many other galaxies, is more densely crouded with stars than the outer region, and contains a massive central object, Sagittarius A*.

Below we give some data for the Galactic Center (this and all following positions for epoch 2000.0):

The Galactic North Pole is at

The coordinate data given here were extracted from the online coordinate calculator at Nasa/IPAC's Extragalactical Database (NED).

Our Sun, together with the whole Solar System, is orbiting the Galactic Center at the distance given, on a nearly circular orbit. We are moving at about 250 km/sec, and need about 220 million years to complete one orbit (so the Solar System has orbited the Galactic Center about 20 to 21 times since its formation about 4.6 billion years ago).

In addition to the overall Galactic Rotation, the solar system is moving between the neighboring stars (peculiar motion) at a velocity of about 20 km/s, to a direction called "Solar Apex," at the approximate position RA=18:01, Dec=+26 (2000.0); this motion has been discovered by William Herschel in 1783.

Considering the sense of rotation, the Galaxy, at the Sun's position, is rotating toward the direction of Right Ascension 21:12.0, Declination +48:19. This shows that it rotates "backward" in the Galactic coordinate system, i.e. the Galactic North Pole is actually a physical South Pole with respect to galactic rotation (defined by the direction of the angular momentum vector).

• More info on the Milky Way Spiral Structure
• Messier Objects in the Milky Way page

• Milky Way Galaxy images from the Astronomical Picture of the Day archives
• Milky Way Wide-Angle Photos
• Multi Wavelength Images of the Milky Way (Nasa ADC)
• Milky Way page of the MAP space observatory project
• The Summer Milky Way from S.E. Arizona
• Milky Way panorama by Axel Mellinger
• The Milky Way Galaxy within 50,000 light years, A Map of the Milky Way, and The Milky Way's Satellite Galaxies, from An Atlas of the Universe
• The Structure of the Milky Way Tutorial, Gene Smith
• Yahoo's index of Milky Way webpages

• D.H. McNamara, J.B. Madsen, J. Barnes, and B.F. Erickson, 2000. The Distance to the Galactic Center. Publications of the Astronomical Society of the Pacific, Vol. 112, pp. 202-216 (Feb. 2000) [ADS: 2000PASP..112..202M]

• The Milky Way, by Bart J. and Priscilla F. Bok. 5th edition. Harvard University Press, 1981.
• The Guide to the Galaxy, by Nigel Henbest and Heather Cooper. Cambridge University Press, 1994.
• The Alchemy of the Heavens, by Ken Croswell. Anchor Books, New York, 1995.

Last Modification: August 25, 2005