Did you make it to the Milky Way? That was my July homework assignment to you, as well as a line from the song “Drops of Jupiter,” by Train. I was reminded of my assignment as my department office manager, Angela, emailed me that title for a list of “celestial” songs I am compiling. I play a topical song while setting up for each Introductory Astronomy class. (YouTube allows me to easily do what was once difficult!)
The rest of September has a moonless, early night sky, so you still have time to sneak out to a dark sky and take in the magnificence of our home galaxy. The Milky Way arcs overhead from north to south, centered overhead just after dark.
You will notice dark patches in it – not areas lacking stars, but rather regions where clouds of dust in our galaxy block the view of more distant stars. This dust is not like the dust bunnies under your bed. This is composed of particles the size of what’s in cigarette smoke. These millionths-of-a-meter grains of silicon- and carbon-based minerals were cooked up in stars and released as the stars aged and died. They may well be the seeds of future stars.
If it were not for the dust in our Milky Way, you would be able to read this newspaper by the galaxy’s light. It limits our naked-eye view of stars to those within just a few thousand light years – just a few percent of what’s in our galaxy’s diameter of 100,000 light years.
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Sorry, but you cannot see any individual stars millions of light years away, in spite of common misconceptions. The farthest you can see with your unaided eyes is on through our galaxy to two neighboring galaxies a couple of million light years away, which are seen as fuzzy patches rising in the northeast in our early evening autumn sky.
This dust was unknown to early astronomers William and Caroline Herschel. They counted the stars in their telescope’s view at hundreds of places along the Milky Way and got about the same number, concluding we must be at the galaxy’s center. (That’s like looking about in a fog and concluding that you were in the middle of the fog based on similar numbers of distant lights seen around you … except you can see the fog. But you can’t see the galaxy dust.)
Later astronomers found that we were not at the center of our galaxy. But it is our home, and it is composed of every star you see in the sky. And we ourselves are composed of stardust. So, be sure to make it to the Milky Way and see the dust whence we came.
Daniel B. Caton is a physics and astronomy professor and director of observatories at Appalachian State University. Email: firstname.lastname@example.org. More on this month’s column: www.upintheair.info.