OUR COSMIC ADDRESS - WHERE ARE WE IN THE UNIVERSE?
Where Are We In the Universe?
Welcome to the beginning of your journey in Year 9 Astronomy. You probably already know that all of space, and time and matter make up the universe, our cosmos (everything). The cosmos is everything that is, was, and ever will be. It is all of space and all of time. As we explore the universe, we quickly discover it is very big. So the first question we may wish to ask ourselves is… where are we in the cosmos? And what else is out there?
The following video will give us a basic overview of the universe.
The following video will give us a basic overview of the universe.
This is the text of the above video:
We live on a planet, Earth, third from the sun. Earth revolves around The Sun with 7 other planets: Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. All together, the sun and its family of planets are collectively known as the Solar System.
But the Sun is just one of billions and billions of stars you find floating through the universe.
The Sun, along with all its family of planets, is found in a region of space we call the Solar Neighbourhood. Other stars that hang out here include, Alpha Centauri (our Sun’s closest neighbour), Sirius (the brightest star in the night sky), Vega (which in the times of the ancient Egyptians (sic - should be cavemen) always pointed people North), and the giant Arcturus… just to name a few.
This solar neighbourhood is just a tiny little town in a big city full of star neighbourhoods… this big city of stars is called The Milky Way Galaxy. The Milky Way Galaxy has over 100 billion stars!
Our star city, the Milky Way Galaxy, is packed with stars and dust in its center, including a super massive black hole at its very heart. The Sun and our solar system keep far away from this busy centre… our solar neighbourhood is found around 1/3 of the way out in the quieter suburbs of the Milky Way, our star city.
The sun and all the other stars in the Milky Way all orbit around the center of the galaxy, powered by gravity. It takes the sun around 225 million years to complete one lap – a galactic year. So far, it has completed a mere 20 laps around the center of our star city – so the sun is around 20 galactic years old. And the sun will only make around 20 more laps, reaching an age of 40 galactic years, before it comes to the end of its active life and settles in to its retirement as a white dwarf.
In general, a galaxy is a collection of billions of stars, all gravitationally bound, which move around a centre.
The Milky Way Galaxy isn’t the only star city around. The universe is full of galaxies. Between galaxies is true empty space, nothing but an occasional hydrogen atom.
The Milky Way Galaxy is around one of 50 galaxies that are gravitationally bound to each other in what is called the Local Galactic Group, or usually just the Local Group. The Milky Way is one of two large galaxies in this group, the other being the Andromeda Galaxy. The rest of the galaxies are much smaller. Some of these smaller galaxies orbit around our galaxy… moons of the Milky Way! Two of these satellite galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, can be seen from Victoria with a naked eye… when you get away from the bright lights of the cities and towns.
Right now, the Milky Way and Andromeda galaxies, the two large star cities in the Local Group, are on track for a head on collision in 4 billion years… but don’t worry… galaxies are mainly empty space… the main thing that changes in galaxy collisions is the overall shape of the galaxies, which will merge into one galaxy… luckily, individual stars rarely collide during such collisions. It’s a relatively safe event and occurs over millions of years.
Beyond the Local Group, things get a little mind blowing. Out here, there are over one hundred billion other galaxies… all moving away from us due to the expansion of the universe. All these other galaxies are far away and move further and further away each second. One day (billions of years from now) they will move beyond our cosmic horizon and will not be visible anymore.
The Local Group, along with many other groups of galaxies, combine to make the Virgo Supercluster, our corner of the universe.
But there are many many super clusters which make up the entire observable universe. What do I mean by observable universe? It means that only part of the universe is visible to us. We have a cosmic horizon! Just like on Earth, the curve of the Earth limits how much of the entire Earth we can see from our home, so it is with the cosmos. There hasn’t been enough time since the big bang for some of the light from distance galaxies to travel through space and reach us.
If we could look at the universe as a whole from a place, somehow outside of the universe, then we would see a structure of two main things: super clusters of galaxies and regions of empty space called voids. The universe would look something like the bubbles that make up the froth at the top of a bubble bath. The surfaces of the bubbles are like the super clusters of galaxies… the empty insides like the voids.
What is beyond the universe? We don’t know. Some people hypothesise that our universe is one of an infinite number of universes in what we call a multiverse. Some people hypothesise that every possible thing that can happen does happen, just in another parallel universe. Each second the universe branches off into an almost infinite number of universes where all possible outcomes do occur in one of them… and your reality collapses into just one of these parallel universes. Just like a tree diagram you made when studying probability, branch after branch more possible universes come into existence… your reality is just one chain in this giant tree. In another universe you are not here but in Consumer Stream making hand lotion. And in another universe, you were never born!
Of course, parallel universes is what we call speculative science… although based on observations and things we do know about… there is no experiment we can do to test if parallel universes are real or not… so it is just speculative.
But the Sun is just one of billions and billions of stars you find floating through the universe.
The Sun, along with all its family of planets, is found in a region of space we call the Solar Neighbourhood. Other stars that hang out here include, Alpha Centauri (our Sun’s closest neighbour), Sirius (the brightest star in the night sky), Vega (which in the times of the ancient Egyptians (sic - should be cavemen) always pointed people North), and the giant Arcturus… just to name a few.
This solar neighbourhood is just a tiny little town in a big city full of star neighbourhoods… this big city of stars is called The Milky Way Galaxy. The Milky Way Galaxy has over 100 billion stars!
Our star city, the Milky Way Galaxy, is packed with stars and dust in its center, including a super massive black hole at its very heart. The Sun and our solar system keep far away from this busy centre… our solar neighbourhood is found around 1/3 of the way out in the quieter suburbs of the Milky Way, our star city.
The sun and all the other stars in the Milky Way all orbit around the center of the galaxy, powered by gravity. It takes the sun around 225 million years to complete one lap – a galactic year. So far, it has completed a mere 20 laps around the center of our star city – so the sun is around 20 galactic years old. And the sun will only make around 20 more laps, reaching an age of 40 galactic years, before it comes to the end of its active life and settles in to its retirement as a white dwarf.
In general, a galaxy is a collection of billions of stars, all gravitationally bound, which move around a centre.
The Milky Way Galaxy isn’t the only star city around. The universe is full of galaxies. Between galaxies is true empty space, nothing but an occasional hydrogen atom.
The Milky Way Galaxy is around one of 50 galaxies that are gravitationally bound to each other in what is called the Local Galactic Group, or usually just the Local Group. The Milky Way is one of two large galaxies in this group, the other being the Andromeda Galaxy. The rest of the galaxies are much smaller. Some of these smaller galaxies orbit around our galaxy… moons of the Milky Way! Two of these satellite galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, can be seen from Victoria with a naked eye… when you get away from the bright lights of the cities and towns.
Right now, the Milky Way and Andromeda galaxies, the two large star cities in the Local Group, are on track for a head on collision in 4 billion years… but don’t worry… galaxies are mainly empty space… the main thing that changes in galaxy collisions is the overall shape of the galaxies, which will merge into one galaxy… luckily, individual stars rarely collide during such collisions. It’s a relatively safe event and occurs over millions of years.
Beyond the Local Group, things get a little mind blowing. Out here, there are over one hundred billion other galaxies… all moving away from us due to the expansion of the universe. All these other galaxies are far away and move further and further away each second. One day (billions of years from now) they will move beyond our cosmic horizon and will not be visible anymore.
The Local Group, along with many other groups of galaxies, combine to make the Virgo Supercluster, our corner of the universe.
But there are many many super clusters which make up the entire observable universe. What do I mean by observable universe? It means that only part of the universe is visible to us. We have a cosmic horizon! Just like on Earth, the curve of the Earth limits how much of the entire Earth we can see from our home, so it is with the cosmos. There hasn’t been enough time since the big bang for some of the light from distance galaxies to travel through space and reach us.
If we could look at the universe as a whole from a place, somehow outside of the universe, then we would see a structure of two main things: super clusters of galaxies and regions of empty space called voids. The universe would look something like the bubbles that make up the froth at the top of a bubble bath. The surfaces of the bubbles are like the super clusters of galaxies… the empty insides like the voids.
What is beyond the universe? We don’t know. Some people hypothesise that our universe is one of an infinite number of universes in what we call a multiverse. Some people hypothesise that every possible thing that can happen does happen, just in another parallel universe. Each second the universe branches off into an almost infinite number of universes where all possible outcomes do occur in one of them… and your reality collapses into just one of these parallel universes. Just like a tree diagram you made when studying probability, branch after branch more possible universes come into existence… your reality is just one chain in this giant tree. In another universe you are not here but in Consumer Stream making hand lotion. And in another universe, you were never born!
Of course, parallel universes is what we call speculative science… although based on observations and things we do know about… there is no experiment we can do to test if parallel universes are real or not… so it is just speculative.
Our Cosmic Address
When you go overseas, you often put your name and address on a tag and attach it to your luggage. That way, if the luggage gets sent on the wrong plane, or you accidentally leave it somewhere on the other side of the world... through the international postal service, it will eventually get back to you.
On Earth, Avila’s address would be:
When you go overseas, you often put your name and address on a tag and attach it to your luggage. That way, if the luggage gets sent on the wrong plane, or you accidentally leave it somewhere on the other side of the world... through the international postal service, it will eventually get back to you.
On Earth, Avila’s address would be:
35 Charles Street
Mount Waverley 3178
Victoria
Australia
Mount Waverley 3178
Victoria
Australia
In the Universe, which has over 70 sextillion stars, 20% of them with planets, we couldn’t count on aliens knowing where Australia was in the vast universe. We’d need to be more specific about where we are. We’d need a cosmic address.
Our Cosmic address may look something like this:
Our Cosmic address may look something like this:
35 Charles Street
Mount Waverley 3178
Victoria
Australia
Earth
Solar System
Milky Way Galaxy
The Local Group
Virgo Supercluster
The Universe
Mount Waverley 3178
Victoria
Australia
Earth
Solar System
Milky Way Galaxy
The Local Group
Virgo Supercluster
The Universe
That’s a pretty detailed address. But in a universe as vast as ours, it needs to be. Let’s look at some scaled images of some of these places, starting with Earth... let's watch astrophysicist, Neil Degrasse Tyson, tell us a little more:
Gallery of our Cosmic Address
Now take your time to get to know this cosmic address a little more. The following slide show runs through each part of the cosmic address in some detail. In this gallery, each subsequent picture zooms out enough to make the previous image just a speck in the middle. Earth is always centred.
Seeing the Cosmos in one Take -
Mega Zoom Out with Morgan Freeman
In the following video, Morgan Freeman takes you on a journey, zooming out from Earth, to a vantage point that looks across the entire observable universe. Notice how the universe's scales seems to fluctuate between regions of complete emptiness and things clustered together. It should give you an idea of just how empty and vast the universe is.
OPTIONAL: Another video of a super zoomout - The Original 1970s version which Morgan Freeman ripped off.
This isn't as impressive, and the narrator's voice isn't as soothing as Morgan Freeman's voice, but this is the original zoom out video which tried to be as accurate as possible to the universe as it was understood then. As you watch it, see if you can keep guessing what's going to appear next, based on what you have learnt so far.
Summary: What you Need to Know
* Know our Cosmic Address from Earth and beyond
* Know the 7 planets in order (covered in next chapter)
* Know that Sirius is the brightest star in our night sky and that Alpha Centauri (aka Rigel Kentaurus) is the closest star to the sun.
* Know that the Sun lies around 1/3rd out from the centre of the Milky Way in a less dense and more peaceful place
* Know the Milky Way has a supermassive black hole at its very centre
* Know that the Milky Way is one of 2 large galaxies in the Local Group - the other being the Andromeda Galaxy
* Know that the Large and Small Magellanic Clouds are small galaxies that orbit around the Milky Way and can be seen with the naked eye from Victoria
* Know that in around 4 billion years, the Milky Way and Andromeda galaxies will collide and merge
* Know that the universe is structured with regions of superclusters of galaxies and voids - large regions of empty space
THAT'S IT!!!
What you need to be able to do:
* Answer facts from the list above
* Be able to identify which part of our cosmic address is being shown in a picture from sizes of key objects... e.g. If the milky way is smallish but bigger than a dot... you must be looking at the local group... if the Earth is small but noticeable, then it must be the solar system... etc. etc.
* Know our Cosmic Address from Earth and beyond
* Know the 7 planets in order (covered in next chapter)
* Know that Sirius is the brightest star in our night sky and that Alpha Centauri (aka Rigel Kentaurus) is the closest star to the sun.
* Know that the Sun lies around 1/3rd out from the centre of the Milky Way in a less dense and more peaceful place
* Know the Milky Way has a supermassive black hole at its very centre
* Know that the Milky Way is one of 2 large galaxies in the Local Group - the other being the Andromeda Galaxy
* Know that the Large and Small Magellanic Clouds are small galaxies that orbit around the Milky Way and can be seen with the naked eye from Victoria
* Know that in around 4 billion years, the Milky Way and Andromeda galaxies will collide and merge
* Know that the universe is structured with regions of superclusters of galaxies and voids - large regions of empty space
THAT'S IT!!!
What you need to be able to do:
* Answer facts from the list above
* Be able to identify which part of our cosmic address is being shown in a picture from sizes of key objects... e.g. If the milky way is smallish but bigger than a dot... you must be looking at the local group... if the Earth is small but noticeable, then it must be the solar system... etc. etc.