The Milky Way we see
September and the fall season are just around the corner. However, the Milky Way is almost directly overhead and many beautiful things can be seen along this starry path.
The Milky Way we see is the northern half of the next arm of our galaxy and this arm is inside the arm where the Sun is located. [To see the other half of the Milky Way, below our horizon, one would need to be below the equator, say, in Australia.] Our Milky Way is a spiral galaxy, and all spiral galaxies have arms extending outward from their cores. We live in the Orion arm and we look toward the Sagittarius arm when we see the Milky Way overhead.
Stars are formed in the arms of spiral galaxies and this is true of the arms of the Milky Way. All stars form in their beginning from ambient clouds of hydrogen gas. The gravity produced by the mass of the gas attracts the cloud of gas inward. If conditions are just right, the clouds will contract so densely that thermonuclear fusion will take place and stars will form, giving off their light in all wavelengths that they can produce.
In these clouds of star-forming gas, some stars will be born before others. These early stars will be very hot and they will give off much ultraviolet light. As this ultraviolet light strikes the hydrogen gas, it causes the gas to fluoresce. The characteristic color of this stimulated gas is a deep red color and many amateur astrophotographers delight in capturing this color.
I have included an image I made of a muchphotographed fluorescing hydrogen cloud located near the constellation Sagittarius. It is called the Lagoon Nebula — see if you think it looks like a lagoon — or something else. Use your imagination.
If you examine the image closely, you will see that many stars have already formed, shining by their own light. However, there is still plenty of hydrogen gas left to fluoresce. Someday, all the gas will have turned into stars or have been blown away by the radiation pressure of new stars. These new stars will then shine by their own light too…
Star-forming regions can be seen in many other spiral galaxies too. Our Milky Way galaxy is undergoing the same processes as other galaxies are — far, far away.
Saturn and Jupiter can easily be seen in the south, southeast at full night darkness. They both appear yellowish and are about two fists above the horizon. Even a small telescope will show mighty Jupiter and four of its moons and about a sixinch telescope will nicely show Saturn’s rings. These are wonderful sights, especially if this is the first time you have seen these wonders!
As long as I am able, as the seasons move on, I will continue to tell you what I can about the remarkable night sky and its contents.