Greetings, stargazers.
The Milky Way is a barred-spiral galaxy about 100,000 light years in diameter, but only about 1,000 light years thick. It contains more than 100 billion stars, and some estimates place that number significantly higher. The sun is a bit over halfway between the center and the edge and makes an orbit around the center every 230 million years or so. On that time scale, the sun has only completed a score of orbits around the Milky Way since the solar system first formed. Jumping into the future by the same amount of time, we can expect the Milky Way to collide with the Andromeda galaxy a little before the sun runs out of hydrogen in its core.
When galaxies collide, the gravitational effects will certainly distort the overall structures, but individual star systems could easily be unaffected. I have heard such collisions compared to two swarms of bees colliding, but the separation between each bee is a couple of miles. The chance of any two bees (or stars in the case of the galaxies) actually colliding is extremely small.
Many of these numbers have rather large uncertainties, but that seems reasonable if you realize that it was barely 100 years ago that anyone recognized that the Milky Way was a galaxy at all. It was determined to be only one of many of the faint “spiral nebulae” that could be seen through telescopes.
The presence of a bar structure in the Milky Way has only been widely accepted in the last 20 years. The bar is a linear concentration of stars centered on the galaxy’s core and extending part way out into the spiral structure. Many other galaxies have bars too, but the reason is not well understood.
It is recognized today that the brightest visible part is in the direction of the center of the Milky Way, but it was the distribution of globular clusters that first pinned down the correct direction and approximate distance to the center. When the distance to all the known globular clusters was determined early in the 20th century, Harlow Shapely used this information to make a three-dimensional map that showed a spherical distribution. This sphere was not centered around the sun as expected. Instead, it was centered about some distant point that we now know to be the center of the galaxy.
Useful links
Milky Way
https://en.wikipedia.org/wiki/Milky_Way
Trifid Nebula
https://en.wikipedia.org/wiki/Trifid_Nebula
Astronomy picture of the day
http://apod.nasa.gov/apod/
An Astronomer’s forecast for Durango
http://www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory
http://www.fortlewis.edu/observatory
hakes_c@fortlewis.edu
The brightest part of the Milky Way surrounds a massive black hole in the center of our galaxy. It will be in the southeastern sky in the direction of the constellation Sagittarius right after dark. The modern asterism associated with Sagittarius is the outline of a teapot. The Milky Way is then seen as the steam rising out of the spout. This is one of the most rewarding regions in the entire sky, as there are numerous targets for your naked eyes, small binoculars or for any size telescope, and it is worth repeating my list of favorite nebulae in this direction.
M8, the Lagoon Nebula is about 5 degrees to the west of the lid of the teapot. It is visible to the naked eye as a faint fuzzy patch. After the Orion Nebula, the Lagoon Nebula is the second brightest star-forming region we can see. With binoculars, numerous stars are visible as part of the open cluster associated with the nebula. The glowing hydrogen gas that makes M8 so interesting will show up red in photographs, but because of the limitations of our eye sensitivity, we will only see this as a pale blue-gray fuzzy patch.
Slightly to the north of M8 is M20, the Trifid Nebula. Dark bands divide this nebula into three, thus its name. Photographs show that half this nebula is blue instead of red. This is a reflection nebula, in which light from the bright nearby stars is scattered by interstellar gas and dust. Just like our atmosphere, blue light is more easily scattered, so this nebula has the same coloring as our daytime sky.
Following the Milky Way to the north, you will see M17, called either the Omega Nebula, the Swan Nebula or the Checkmark Nebula depending on what your imagination says it looks like. Beyond M17 is M16, the Eagle Nebula. A prominent feature of the Eagle Nebula became famous as the “pillars of creation” photo taken using the Hubble Space Telescope.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
