On clear, dark nights around the 285 corridor, you can see the Milky Way rise above the horizon and span the sky. The Milky Way isn’t just a pretty band of stars, it’s a barred spiral galaxy that we reside within. The center of the galaxy is a rectangular bar with arms spiraling around it.
Our galaxy consists of 100 – 400 billion stars, dark dust clouds, and gaseous nebulae, within which new stars are born. The dust clouds and nebulae hide many stars within the Milky Way, making it hard to determine the total number of stars in our galaxy, hence the wide range in the above-mentioned estimate.
At the galactic center is a supermassive black hole, Sagittarius A* (pronounced, ‘Sagittarius A Star’). A black hole is an object that gravitationally collapsed upon itself, leaving a region of space whose gravity is so strong that not even light can escape from it. A supermassive black hole is, well, supermassive! It’s a black hole millions, possibly billions of times the mass of the Sun. Most large galaxies have supermassive black holes at their galactic centers.
It’s difficult to visualize the spiral nature of our galaxy since we reside within it. The Sun we orbit is an average star, located far from the center of the galaxy. By observing the Milky Way from our vantage point, it’s obvious that our galaxy is relatively flat, with a bulging center.
If we were able to observe the Milky Way Galaxy from ‘overhead,’ we’d see a minor ‘arm’ coming off of each end of the central bar. One of these minor arms is called the ‘Near 3kpc Arm,’ the other is the ‘Far 3kpc Arm.’ The Near 3kpc Arm appears to run from one end of the central bar to the other, then transitions into one of the two major spiral arms, the Perseus Arm. The Far 3kpc Arm appears to start at the end of the bar opposite the Near 3kpc Arm and goes to the other side of the bar, turning into the second major spiral arm of our galaxy, the Scutum-Centaurus Arm.
This hypothetical view looking down on the Milky Way Galaxy is courtesy of NASA.
Between the galactic bar and the Scutum-Centaurus Arm is another minor arm, called the Norma Arm. This arm spirals around the bar, becoming the Outer Arm, which runs outside of and roughly parallel to the Perseus Arm.
Between the galactic bar and the Perseus Arm is a minor arm known as the Sagittarius Arm. As the Sagittarius Arm spirals outward from the bar, it becomes the Carina Arm.
There’s a ‘star bridge’ connecting the Sagittarius Arm to the Perseus Arm. This bridge is known as the Orion Spur (sometimes called the Orion-Cygnus Arm). Our solar system is located on the inner rim of the Orion Spur.
Tightly packed groups of stars known as ‘globular clusters’ form a halo around the galactic center. Globular clusters are made up of hundreds of thousands of stars, tightly bound by gravitational attraction. Globular clusters are common in the halos of spiral galaxies (there are more than 150 globular clusters surrounding the galactic core of the Milky Way), but their formation remains poorly understood.
While there are many fantastic photos of the Milky Way viewed from our perch within it, I haven’t found a detailed map showing the names of the various structures that can be seen with the unaided eye. So, I decided to make my own (so as not to clutter the map, I elected to not label Messier objects).
I lack the skill and equipment to capture the entire Milky Way Galaxy in one image, so I broke it down into several photos (also, a good portion of the Milky Way can’t be viewed from our location because it extends far into the southern sky).
Here’s one example of the maps I made (along with the same photo, sans labels), showing the portion of the Milky Way toward the galactic core, looking through the Sagittarius arm, as seen from Earth.
In this map, the Milky Way begins in Scorpius on the southern horizon at the right, moves left to the galactic center in Sagittarius, then begins to flatten as the galactic bulge transitions to a flat disk, spanning the constellations Scutum, Aquila, and Cygnus (far left).
As you can see, the view of the Milky Way is one of faint clouds of stars, too thick to count, along with areas of darkness that, at times, appear mottled and, at other times, appear like they’ve been swept in a particular direction by an unseen force.
The dark areas, often referred to as ‘molecular clouds,’ are giant clouds of dust and gas that block the light of myriad stars behind them. We tend to focus on the star clouds, but the dust clouds are also worthy of notice since some of them are major areas of star formation – stellar nurseries, if you will.
How much detail you can see when you look at the Milky Way is dependent upon a number of factors. A clear, dark night is necessary to see its overall structure. But, atmospheric transparency (the amount of water vapor in the air) and ‘seeing’ (the degree of atmospheric turbulence) are also important. When these factors are all favorable, the resulting view of the Milky Way is nothing short of spectacular, even to the unaided eye.
So, take advantage of our dark night skies and become familiar with the galaxy we live in. View it as a whole or use binoculars or a telescope and break it into small portions. You can spend a lifetime observing the Milky Way and never learn all its secrets.