Our Place in the Milky Way Galaxy
If a solar system is like a home village, then a galaxy is like a very large home country. Our Sun and its collection of planets and other assorted celestial bodies is just a very small part of a much larger assembly of many such systems, bound by gravity and orbiting around the center of this large mass. It is a system of circles within circles. Our planets go around the Sun, the Sun goes around the Galactic Center, and the Milky Way in turn orbits the center of the local cluster of galaxies.
In our time we have barely begun to explore our village. We’ve been to the Moon (the little side street next door), but that’s it so far. In Star Trek’s time we have visited other villages and started to map out some provinces. But even Archer, Kirk, Picard, and Sisko and their crews have not yet seen much outside their local few provinces. Janeway & Co. were further away than anyone else from our neck of the woods, but on their way home they mostly explored what was in their path.
In order to figure out the shape and content of our Milky Way, we need to be able to visualize the whole Galaxy, and we need to determine where we are in respect to everything else. When you look up at the sky on a clear night, you see a dense band of stars and darker stuff. That is the disk of our Milky Way. As it turns out, we are inside this disk, so when we look along the disk, we see a much denser assembly of stars and clouds (the darker stuff). When we look away from the disk, towards Galactic North or Galactic South, we see some stars of our Milky Way, but also see the distant galaxies in intergalactic space.
Our Solar System and all the worlds we will know in Star Trek’s time are in this disk of the Milky Way. We can imagine our galaxy like two soup plates stuck together, the bulge in the middle is the bulge, and the outer flatter part is the disk.
Figure 2: The Milky Way disk in Star Trek’s time. Credit: Ex Astris Scientia.
So, how do astronomers (in our and any other time) figure out what our galaxy looks like? The shape of other galaxies seems obvious, but that’s because we’re looking at them from the outside, and we can see the whole thing. In the case of the Milky Way, we’re stuck inside. We need to be able to look through a lot of the clouds and dense stuff to discern the structure.
What stuff you can see through depends on the relationship between the sizes of the atoms and dust particles you’re trying to look through and the wavelength you are using. The light our eyes can see, the visual wavelengths, are fairly short (400 to 700 nanometers). A lot of the stuff in the clouds is bigger than that, so we can’t see through these clouds easily. Therefore we need to use longer wavelengths, for example infrared (somewhat longer than visual) or radio (a lot longer than visual) wavelengths.
Using radio astronomy observations from various facilities we have previously figured out what our Milky Way looks like inside, that it is a spiral galaxy with multiple arms, and that our Sun is located in the disk, about halfway to two-thirds out from the core, in between two major spiral arms of the galaxy, the Sagittarius Arm and the Perseus Arm. The former is further inward, the latter further outward from the Galactic core.
Today we use multiple coordinated radio telescopes, such as the Very Long Baseline Array (VLBA) to figure out more details about our Milky Way. The VLBA uses ten 25-meter-diameter radio antennas located all the way from Hawaii to St. Croix in the Caribbean in order to achieve very high precision in their measurements. Recently, astronomers using the VLBA have determined that we in our Solar System do not just reside in some minor local skinny arm of the Galaxy, but that the local arm is almost as prominent as the Sagittarius and Perseus Arms. This might mean that we are in a denser region of the Galaxy than we thought, it might also mean, that in Star Trek’s time, there are likely more worlds closer to us, and that we are not such a backwater place after all. The Federation might be a lot busier than we imagined.
Figures 3 and 4: former (left) and new (right) view of the Milky Way and our place in it. Credit: Robert Hurt, IPAC; Bill Saxton, NRAO/AUI/NSF.
While contemplating this issue, something related popped into my head. Given that we today can use longer wavelengths to see through clouds of gas and dust in galaxies, I’ve always wondered why starship captains think that they can hide from other ships inside clouds. There are a few cases in Star Trek lore that come to mind. Why not just tune your main sensor to longer wavelenghts and presto, no more hide and seek. But that’s a topic for another time.
Here are a few links if you’d like to know more about this topic.
The NRAO announcement on “Earth’s Milky Way Neighborhood Gets More Respect”:
http://www.nrao.edu/pr/2013/localarm
Las Cumbres Observatory Global Telescope Network:
http://lcogt.net/education/article/milky-way-galaxy
Ex Astris Scientia:
http://www.ex-astris-scientia.org/index.htm
If you are interested in hearing more about the latest discoveries in the physical sciences and technology in a fannish setting, come visit us at Shore Leave this coming August. This fan-run convention features over 12 hours of science programming, in addition of course to all the usual con activities. For more information please visit http://www.shore-leave.com.
Inge Heyer
www.ingeheyer.com
