Chapter 3— The scale of the Cosmos
Introduction
Yes finally, we’re going to start with something Astrophysics related! Now before we delve in, I’m legally obligated to tell you that this is a point of no return.
During the course of this article, you will be exposed to the prettiest of pictures and the most interesting facts. In fact your mind is probably not going to comprehend what will be covered because it’s just — mind blowing. Let’s go!
“The size and age of the Cosmos are beyond ordinary human understanding. Lost somewhere between immensity and eternity is our tiny planetary home.”
Carl Sagan
Where do we live?
We live in the universe. Let me be more specific, we live in a galaxy. Let me be more specific, we live in the solar system. Let me be more specific, we live on a planet. Once again, let me be more specific, we live on the Earth.
The Earth is a planet, more specifically, the third planet in the solar system. It has a diameter of 12,742 km and supports life. The reason the Earth supports life and no other planet on the Solar System does to our knowledge is because of how far the Earth is from the Sun.
The Sun is a star that we orbit. We are at the perfect distance from the Sun, in what is known as the “habitable zone.” We are neither too far that is too cold for life, nor too close that is too hot for life.
The Solar System
The Solar System is essentially a collection of objects (planets, asteroids, dwarf planets) that orbit the Sun. There are 8 planets in the Solar System
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus (Please be mature thanks)
- Neptune
- Plu… No Pluto doesn’t count jeez
As you can see, some planets are much larger than the Earth and some much smaller.
The solar system also has asteroid belts, they are essentially just rings of asteroids, we’ll cover them later!
Just how large is the solar system? Well if you define the Solar System as the region in space influenced by Sun’s gravity, then it would be around 123 AU. If you remember the definition of the AU from our last post, you’d remember that this means that the solar system is 123 times longer than the distance from the Earth and the Sun.
What lies beyond?
As we go further from the Sun we reach the boundary of this bubble like thing called the heliosphere. It is essentially this bubble that is formed by solar wind — charged particles released from the Sun. The boundary is known as the heliopause and is around 123 AU away from the Sun.
The Oort cloud
What happens if we go past the heliosphere. We reach this hypothetical structure known as the Oort cloud. The Oort cloud is this spherical structure which contains ice, ammonia and methane that was left over from the creation of the solar system. In fact the Oort cloud is so big that it is estimated to be around 2000 to 10000 AU away from the Sun. The closest star to the Earth is Proxima Centauri which is about 4 ly away from the Sun. This means that it is not within our solar system and it is possible that these stars have Oort clouds of their own.
What happens if you go further?
If you somehow manage to survive the harsh conditions present in the Oort cloud, you’d really just be floating in space. So to get to the real fun stuff, let’s zoom out a bit
The galaxy
“A long time ago in a galaxy far far away.”
George Lucas
Star Wars music stops playing*. Ah Yes, the galaxy. We live in a galaxy known as the Milky Way. The reason it’s called the Milky Way is because of a Greek Myth in which the Goddess Hera sprayed milk across the sky.
Now the Milky Way is massive. If you thought the Oort cloud was really far away from us, you’d be surprised at how we’re represented on the Milky Way.
We’re not even a dot nor a speck, just a mere pixel on this image. The Milky Way is about 105,700 ly in diameter. That means it takes light 105,700 years to travel from one end of the Milky Way to another. Don’t forget that light travels at 3.0 x 10⁸ km/s. Now the Milky Way is quite huge but how huge is it? How many planets does the Milky Way have. It is estimated that there around 400 billion or 4.0 x 10¹¹ planets. So many of them could be in the habitable zone of their star, so man of them could be good enough if not better for human survival. However we have a long way to go before we can even think about intergalactic travel.
Where is our galaxy?
Our Milky Way is part of a group of galaxies known as the “Local Cluster.”
The Local Cluster is roughly 3 Mpc in diameter. If you remember the metric multiplier table in one of my earlier posts, this stands for 3 Megaparsecs which is around 10 million or 1 x 10⁷ ly in diameter. The Local Cluster also known as the Local Group contains other galaxies such as the Andromeda Galaxy and Triangulum.
The largest galaxy in the Local Cluster is Andromeda. It is closely followed by the Milky Way and Triangulum.
The Universe
Beyond the Local Group are more galaxy clusters, some larger than the Local Cluster and some smaller. Either way, we’re nearing the end of us zooming out. The Universe is everything. It is the most vague and mysterious thing in well, the Universe but at the same time discoveries are being made daily. The Universe is about 93 billion light years in diameter and it is constantly expanding. It is estimated that it is expanding at a rate of 67–74 km/s per Mpc.
The Universe is extremely vast, so huge that we cannot comprehend the size of it. How can we if we can’t even comprehend the size of the Sun? The fascinating fact about Space in general is that we think we understand it, we think we know what it is and we think we know how huge it is, but we really don’t. It’s beyond our level of comprehension and it’s likely to stay like this for a very long time. For now we can only think of the Universe as some entity beyond our understanding, but in reality it’s much more than that.
Conclusion
I hope you enjoyed today’s post, unfortunately writing cannot accurately convey enthusiasm. I highly recommend you watch the videos on Khan Academy if you really want to learn about this topic a bit more as the video really quantifies the information in this article. In the next post, we’ll be looking at Galactic Coordinates.
- Scale of the Earth and Sun: https://www.youtube.com/watch?v=GZx3U0dbASg
- Scale of the Solar System: https://www.youtube.com/watch?v=GP53b__h4ew
- Scale of the Galaxy: https://www.youtube.com/watch?v=rcLnMe1ELPA
- Intergalactic Scale: https://www.youtube.com/watch?v=rcLnMe1ELPA
Images can be found at (some sources have been cited under the image):
- https://www.universetoday.com/106062/what-is-the-milky-way-2/
- https://earthsky.org/upl/2014/01/sun-milky-way-location-Caltech.jpg
- https://en.wikipedia.org/wiki/Local_Group
- https://en.wikipedia.org/wiki/Andromeda_Galaxy
- https://upload.wikimedia.org/wikipedia/commons/thumb/6/64/VST_snaps_a_very_detailed_view_of_the_Triangulum_Galaxy.jpg/1200px-VST_snaps_a_very_detailed_view_of_the_Triangulum_Galaxy.jpg
