In our discussion regarding THE Timeline .... a number of considerations come into play. The full picture is yet to emerge, however, some key attributes and considerations can be listed at this time.  Among them is the question of the significance and ramification of collisions of galaxies.

"Collision Scenario for the Milky Way and Andromeda Galaxies - The Milky Way and the Andromeda galaxy are approaching each other with a speed of 300,000 miles per hour. " - so reads a 1997 AstroFile. The discussion continues to state " A direct collision would lead to a grand merger between the two behemoths, and the Milky Way would no longer be the pinwheel spiral we are familiar with, but would evolve into a huge elliptical galaxy. It would happen no sooner than five billion years in the future. By then the Sun may have burned out, and the Earth reduced to a frigid, lifeless cinder. It's impossible to predict if there would be any vestige of humanity colonized among the stars, not to mention extraterrestrial civilizations around to witness this great collision. "

What does this all mean? Is there any truth to this?   According to STScI-PR97-34 October 21, 1997  the Hubble Space Telescope image below provided a detailed look at the "fireworks show" showing a collision between two galaxies where  it was claimed that "over 1,000 bright, young star clusters were seen "bursting to life" as a result of the head-on wreck"

- Yale theorist Beatrice Tinsley whose research entails modeling how entire populations of stars age within a galaxy, concludes that galaxies can undergo substantial internal evolution through time, more than previously assumed.

   In a different venue, when considering Galaxy Classifications, one finds that there's he ARP catalog (VII/170 Catalogue of Southern Peculiar Galaxies and Associations (Arp+, 1987) where one one sees the following description codes:

1 Galaxies with interacting companion(s)
2 Interacting doubles (galaxies of comparable size)
3 Interacting triples
4 Interacting quartets
5 Interacting quintets
6 Ring galaxies (or morphologically similar objects)
7 Galaxies with (linear) jets
8 Galaxies with apparent companion(s)
9 M51-types (companion at end of spiral arm)
10 Galaxies with peculiar spiral arms
11 Three-armed spirals and multiple-armed spirals
12 Peculiar disks (major asymmetry or deformation)
13 Compact (very high-surface-brightness) galaxies
14 Galaxies with prominent or unusual dust absorption
15 Galaxies with tails, loops of material or debris
16 Irregular or disturbed, (apparently isolated) galaxies
17 Chains (four or more galaxies aligned)
18 Groups (four or more galaxies not aligned)
19 Clusters (only very conspicuous, rich systems)
20 Dwarf galaxies (low surface brightness)
21 Stellar objects with associated nebulosity
22 Miscellaneous (rare or distinctive objects)
23 Close pairs (not visibly interacting)
24 Clode triples (not visibly interacting)
25 Planetary nebulae

What does this all lead to?  More discussion to come.

Bibliography:

1. Abell's Exploration of the Universe   by David Morrison, Sidney C. Wolff, Andrew Fraknoi (this one's the best ...)

2.  Hubble Revisited: New Images From the Discovery Machine   by Daniel Fischer, Hilmar W. Duerbeck.

3. A Journey Through Time : Exploring the Universe With the Hubble Space Telescope by Jay Barbree

4.  Galaxies in the Universe : An Introduction by John S. Gallagher, Linda Siobhan Sparke

5. Galaxy Formation (Astronomy and Astrophysics Library) by Malcolm S. Longair

6. Galaxy Formation by James A. Green

7. The Carnegie Atlas of Galaxies (Carnegie Institution of Washington Publication ; 638)(2 Volume Set) by Allan Sandage

8. 3-D Atlas of the Stars and Galaxies by Richard Monkhouse, John Cox

About the Milky Way:

1. The Formation of the Milky Way : Proceedings of the Iaa-Iac-University of Pisa Workshop, Held in Granada, Spain, September 4-9, 1994 by Iaa-Iac-University of Pisa Workshop, a Delgado

2. Coming of Age in the Milky Way  by Timothy Ferris (Winner of the 1988 American Institute of Physics Prize and named one of 1988's best books by the New York Times Book Review)

3. The Man Who Sold the Milky Way : A Biography of Bart Bok  by David H. Levy

4. The Milky Way by Bart Jan Bok, Priscilla Fairfield Bok(Photographer)

5 The Milky Way and Other Galaxies  by Gregory Vogt   (For kids)

6. Precision Photometry : Astrophysics of the Galaxy : October 3-5, 1990, Meeting Held in Schenectady, New York at Union College (Van Vleck Observatory)
by A.G. Philip

7. A Reference Catalogue and Atlas of Galactic Novae by Hilmar W. Duerbeck

8. Atlas of Galactic Neutral Hydrogen by Dap Hartmann, W. Butler Burton

9. The Center, Bulge, and Disk of the Milky Way (Astrophysics and Space Science Library, Vol 180) by Leo Blitz(Editor)

UPDATES: Milky Way  Galaxy Formation   Galaxies  Astronomy

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