The question of what galaxy is Earth in is not an easy one to answer for many people. Some astronomers have argued that the majority of our planet is in the spiral arm of the Milky Way, while others think our planet is in the flat area surrounding the galaxy. No matter which theory is right, there is no doubt that the question of what galaxy is Earth in has puzzled scientists for decades. Fortunately, there is one scientist who thinks he has found the answer.
First, let’s examine what exactly the word “galaxy” means. In science, a galaxy is a vast collection of very small, numbered stars that makes up the universe. While it is the most common type of galaxy to be compared to, other types are minor collections of stars or gas planets that orbit around other solar system stars. There are also large, elliptical galaxies like our own, which contain extremely massive black holes.
How do we define what the universe is? Astronomy is used to describe the visible universe. Objects that can be seen by telescopes on Earth and those that cannot are thought to be part of the observable universe. Objects that are within the visible part of the universe can be seen by telescopes on the ground and space vehicles such as satellites and landing crafts. Because of the expansion of the universe, all these objects have migrated toward the edges of the visible, thus making it impossible to see all of them at once.
A galaxy can be thought of as a collection of separate smaller galaxies. One galaxy can be thought of as being composed of a globular cluster, while another could be thought of as containing many hundred billions of stars. While most of the clusters are made of cold, dense gasses like water and ammonia, some contain warm, wet stars, which are much easier to observe. Because they are closer to Earth, these stars can be seen as streaks of light, called reflected light, by amateur astronomers on Earth.
Earth and Its Galaxy
While astronomers search for exotics in the outer reaches of the solar system, they also study the Milky Way Galaxy to discover if there are alien worlds orbiting around other, hot stars. While many astronomers use telescopes on earth to study these stars, an even more powerful instrument is being used on the space probe, NASA’s THEMIS. This instrument, designed and operated by the University of Arizona, is able to view infrared filters that are invisible to the human eye. When infrared light is blocked, it is easy to see the tiny dust lanes and cratered surfaces that are typical of alien planets. Since infrared is very common in the environment of alien planets, these results dramatically demonstrate the probability that earth is not alone in its formation.
While astronomers have speculated about the nature of these galaxies for years, determining what is the question that continues to puzzle the cosmos. While many astronomers are convinced that spiral galaxies like our own Milky Way are young and relatively uneventful, other theories cast doubt on this idea. For instance, theories suggest that spiral discs like our own Milky Way are actually in a state of hibernation, slowly reshaping themselves to form bulges of gas and stars that lie much closer to their own centers. Because of the similarities between these two models, astronomers are left trying to reconcile the differences.
Scientists believe that there is a great deal more activity going on in our own Milky Way Galaxy than just spiraling disks. In fact, some theories suggest that our own solar system could be a mini-asteroid belt, a region of low pressure where different sized rocky bodies can cluster together, eventually becoming massive enough to become an asteroid. These collisions are what send material hurtling toward our planet, causing it to spin faster and creating a moon-like planet called Lagrange points. One of the most fascinating predictions comes from the work of planetary astronomers Johnanson and Halpin who believe that many of these Lagrange points are very similar to our own Earth.
So, what galaxy is earth in? That answer is still up in the air as we find more ways of answering this question every day. Although astronomers have spent decades studying the visible universe, they still cannot answer it with certainty. Perhaps one day we will know for sure, but for now, we simply have to take the best chances we can. With over 70% of the known Milky Way’s volume composed of cold atomic gases, it is not surprising that many astronomers feel that earth is in a relatively safe orbit around a very old and cold star.