Astronomy and astrophysics are one of those things I always wished I had the chance to study were it not for the physics part. Somehow everything ended up being pi times the square root of 15 to the 10th power or something. So I admire from afar and leave the complex math and physics to those with an aptitude for such things.
But you don’t need to know MIT level math to find awe and fascination in our universe – which is vast, beautiful, fascinating and seemingly infinite. The scales and distances are so incredible that just citing the numbers won’t give most people a real idea of the immense scales involved. To put things in perspective: the Earth is to our Galaxy what an atom is to our body.
It is humbling and helps put things in perspective to look at the world and our existence from that angle, especially in a world in which most people are obsessed with petty, in the grander scheme of things, irrelevant notions of religion and national identity. We humans are so blinded by our own alleged self importance and the belief that we occupy a privileged position in the universe, that we cannot see anything else but ourselves.
Our most fundamental beliefs pertaining to the nature of existence are deeply rooted in folklore and myth, from which the myriad of world religions have emerged. The belief in some sort of a creator and decision maker pulling the strings has been so entrenched in our civilizations and cultures that stepping away from such a paradigm would in fact require a serious paradigm shift on a very fundamental level. But as long as beliefs in a fantastical and mythical power in the form of religion keep guiding us, we will never be able to step beyond the known and into the unknown that is our universe; our existence.
So what is this universe and where is it vis a vis us? The answer is: The Milky Way Galaxy where life as we know it exists on a small planet in a nine planetary solar system.
The Milky Way Galaxy is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 100–400 billion stars. As a comparison, the neighboring Andromeda Galaxy contains an estimated one trillion stars.
The sun is about 26,000 light-years from the center of the Milky Way Galaxy, located on one of its spiral arms, close to the inner rim of the Galaxy’s Orion Arm, in the Local Fluff inside the Local Bubble, and in the Gould Belt, at a distance of 8.33 ± 0.35 kiloparsecs (27,200 ± 1,100 light years) from the Galactic Center. It takes our solar system roughly 200-250 million years to orbit once around the Milky Way. In this orbit, we (and the rest of the Solar System) are traveling at a velocity of about 155 miles/sec (250 km/sec).
The Milky Way is estimated to be about 13.2 billion years old, nearly as old as the Universe. Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.
The arms of the Milky Way are named for the constellations that are seen in those directions. The major arms of the Milky Way galaxy are the
Centaurus Arm and
Our Solar System is located in the Orion-Cygnus Arm known as the Orion Spur.
The Local Group is the cluster of galaxies to which we belong. It is a group of about 30 galaxies that is about 5 million light-years across. The largest of the galaxies are Andromeda galaxy, Triangulum, and our Milky Way. The Local Group also includes Fornax, the Large and Small Magellanic Clouds, M32, M33, M101, and 9 dwarf spheroidal galaxies. The center of the Local Group is roughly between the Milky Way)
Astronomers believe that only about 10% of the mass of our galaxy comes from stars, gas and dust. They suspect that there must be more matter than we can see because of the way the galaxy rotates. If all of the stars in our galaxy were orbiting a massive object in the center, the way the planets orbit the Sun in the Solar System, then the stars closer to the edge of the galaxy should be orbiting more slowly than stars closer to the center, the same way the outer planets orbit more slowly than the inner ones. Instead, stars near the edge of our galaxy orbit at nearly the same speed as stars nearer the center.
To produce this kind of motion, the galaxy must contain much more mass than we can see. Astronomers theorize that this extra mass is dark matter. This matter is not visible, emits no electromagnetic radiation, and has so far eluded detection.
As a guide to the relative physical scale of the Milky Way, if it were reduced to 100 meters in diameter, the Solar System, including the hypothesized Oort cloud, would be no more than 1 millimeter (0.039 in) in width. The nearest star, Proxima Centauri, would be 4.2 mm (0.17 in) distance and the Andromeda Galaxy, M31. The galaxies in the Local Group are moving in concert with each other, independent of the “Hubble flow” expansion.