Where the heck are we anyhow?

When I was a kid I could lay on the grass and stare into the night sky forever.  Now I live in the city and have no stars and no grass, not to mention that going outside at night is dangerous ... so I look at APOD pics of deep space forever. I wonder how far it goes, I wonder where we fit in it all. Most people have some vague idea that the Earth is part of the Solar System, and the Solar System is stuck in a group of stars called a galaxy, the Milky Way galaxy to be exact. And that's about the extent of it for most people's knowledge of the Universe. Well, I came across a site that had some wonderful illustrations that capture Earth's place in  the cosmos nicely, and it inspired me to write about our place in the greater scheme of things.A tour of the Universe so to speak, starting with our home:


Our Solar System. The Sun at the centre, the four inner planets: Mercury, Venus, Earth, and Mars. Then at a much greater distance, the outer planets Jupiter, Saturn, Uranus, Neptune, and the former planet, Pluto. Toss in an Asteroid Belt and a few comets, and voilà, our familiar solar neighbourhood. Now the fun begins ...

This is our nearby stellar neighbourhood, all of the 33 stars within 12.5 light years of Earth. Most of them aren't even visible to the naked eye because they are red dwarfs, stars with a fraction of the Sun's mass and brightness. About eighty percent of the stars in the Universe are red dwarfs, some have suggested it is them we should be looking at as habitats for life because of their abundance and long lifetimes, trillions of years vs billions of years for stars like our sun. Proxima Centauri is the closest star to the Earth, and it is indeed a red dwarf. Some of the other names on the map may be familiar to Sci Fi and Star Trek fans. Now we step back once again ...

... and see the stars within 250 light years. There's about 260,000 of them, this is a plot of the 1500 most luminous. About a third of the stars visible in the sky are within 250 light years, although we are still looking at just a tiny chunk of the Galaxy. All of these 1500 stars are considerably more luminous than the Sun, although at least the Sun isn't a red dwarf, it's still a small insignificant star already even at this scale. And it gets more insignificant:

Here's the Universe within 5000 light years, our little arm of the Milky Way galaxy, the Orion Arm. Virtually every star we can see with the naked eye from Earth is within this distance. The stars on the plot are all thousands of times brighter than the Sun. The brightest star here is Rho Cassiopeia (ρ Cas,) some 100,000 times brighter than the Sun. At 4000 light years away it is barely visible to the naked eye. And oddly enough, the stars in the constellation Orion's belt really are a grouping of bright stars. Most constellations are just an accident of the fact that we are looking at them from Earth's perspective ... but there is an actual Orion's belt in the Heavens.

OK, this looks familiar again. This is it, the Milky Way galaxy, our Island Universe in the void. This image is about 100,000 light years across, and contains some 200 billion stars. One can see from this perspective that even our arm of the galaxy, the Orion Arm, is a pretty puny and insignificant afterthought. Still we can take comfort in the fact that at least we aren't part of the Sagittarius dwarf galaxy, because those suckers are toast. Yes, they are being sucked into the Milky Way, if one animated the above image the galaxy would spin as Sagittarius got sucked to its doom. Well, its doom as an independent galaxy, its stars will just become part of our glorious Milky Way. It gets better ...

Yes, these are the Milky Way's satellite galaxies. The Milky Way is easily the largest galaxy within 500,000 light years! The twelve dwarf galaxies pictured all orbit the Milk Way. There's some 225 billion stars in this picture, most of them in our galaxy. If our tour stopped here, we could be assured that at least our galaxy was significant. Alas, not as significant as we might like.
 
Here is the local galactic neighbourhood, the Local Group as it is so unimaginatively called. It's about ten million light years wide, contains three large galaxies, 46 dwarf galaxies, and about 700 billion stars. And while the Milky Way is one of the three large galaxies, it's only the second largest. The Andromeda galaxy is larger. Still, we are going to crash into it soon, and with any luck we will strip them of their title. Not for billions of years though. Maybe astronomers called it the "Local Group" as some sort of understatement, our collection of galaxies has to mean something?

Here's the bad news, the Universe within 100 million light years. The Virgo Supercluster, more then 2500 large galaxies, more than 50,000 dwarf galaxies, and some 200 trillion stars. Our little Local Group barely even qualifies as a group on this scale. Well, it was fun while it lasted, at least we aren't in a dwarf galaxy or orbiting a dwarf star, small comfort I know. At least the Virgo supercluster is a big deal, right?

Nope. In this view of the Universe within 1 billion light years, alas, the Virgo supercluster is no big deal. It's just one of 100 odd superclusters, containing some 3 million large galaxies, 60 million dwarf galaxies, and over 250 000 trillion stars. We are, quite literally, so insignificantly small in the greater scheme of things that it's almost impossible to fathom. And even then this map is only about 7 percent of the visible universe. Notice also how the galaxies seem to fall in sheets and lines with big voids in between ...

... because yes, on the grand scale the universe is like foamy bubbles with sheets and clusters of galaxies forming the walls of the bubbles. Why this should be isn't understood, but I think it's just cool that astronomers were able to recognize that the universe isn't just an amorphous soup of galaxies, it has structure even on the largest scale. The visible Universe is all within 14 billion light years, the age of the Universe and the maximum distance light has had to time to travel during the Universe's lifetime, and contains some 10 million superclusters with 350 billion large galaxies, 7 trillion dwarf galaxies (pfft) and some 30 billion trillion  (3x10²²) stars.

And this is just the visible Universe, the actual Universe is much larger than this, and may possibly even be infinitely large, astronomers simply don't know for sure. Coming soon, what strange things do we see at the furthest edge of the visible Universe? And no, I'm not talking about the Cosmic Microwave Background Radiation.

The text on this site is Copyright © Doug Stych, 2009, All Rights Reserved. This site was inspired by the fine Atlas of the Universe by Richard Powell, for far more information and maps of the universe, I highly recommend it. All of the maps and diagrams above belong to Richard Powell, and are free for anyone to use under the following conditions. They are licenced under a Creative Commons Attribution-ShareAlike 2.5 Licence.

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