Our big universe full of wonder
Do you ever wonder where you live? No really- I mean where you really live. If, like the author, you reside in Las Cruces, then you live in the northern part of the western hemisphere on the planet Earth. Once per year, our fragile little planet completes an orbit around our star. That star is about 93 million miles away. Light, traveling 186,000 miles per second, can circle our Earth seven times in a single second. At that speed, it takes sunlight a little over eight minutes to reach Earth. When you see the sun, you are experiencing it as it was a little over eight minutes ago. Also orbiting our sun are eight other planets plus multiple dwarf planets and countless asteroids. The dwarf planet Pluto orbits so far away that it takes sunlight six hours to reach it.
There’s more. Our sun and its planets live in a system of stars called the Milky Way Galaxy. It consists of about 400 billion stars like our sun. The average distance between these stars is about 10 light years (meaning it takes 10 years for light from any average star to reach its nearest star). Let’s put that into perspective, if you could shrink our solar system to the size of a dinner plate with Pluto orbiting around its outer edge, then on that scale the sun would be smaller than pinhead and the nearest star would be in Albuquerque. That is a lot of empty space!
These billions of stars are orbiting around the center of the Milky Way, which, by the way, hosts a blackhole so massive it has the mass of over four million suns! Fear and loathe not! The distance to the center of our galaxy is 30,000 light years, or 3000 times farther than the nearest stars. In our dinner plate model of our solar system, the blackhole would be two and a half times further away than the moon. In the real world, the moon is 240,000 miles away, so, yeah, we’re OK! It takes our sun about 250 million years to make one orbit around the center of the Milky Way. Given that our sun is about 4.5 billion years old, in its lifetime, it has made about 20 orbits around the Milky Way. It soon will have its 21st birthday and go on a Galactic pub crawl. Just joking.
Now, hold on to your hat because there is even more. Our Milky Way galaxy is not alone. It is one of hundreds of billions of galaxies in the universe. And each of these galaxies has hundreds of billions of stars orbiting around their central black holes! The nearest large galaxy to us is called Andromeda and it is about 2 million light years away. We see starlight from all the stars in Andromeda after it has traveled through space for 2 million years; we are experiencing this galaxy as it looked 2 million years ago! The Milky Way and Andromeda have about 50 small galactic “friends,” smaller galaxies all orbiting around in a little group. We call this the Local Group. A fun fact is that in some 4 billion years from now the Andromeda and Milky Way will collide, but their billions of stars will never touch! Imagine what the night sky would look like then!
And ... there’s more. Much more. Our humble little Local Group is in the suburbs of “The Big City." This metropolitan region of space is the Virgo Cluster, a huge group of some 2000 galaxies that is 50 million light years away from our Local Group. That distance is about 1/2000th of the size of the visible universe. Virgo is at the center of a three-dimensional cosmic web along which galaxies and other “local groups” are strung along like beads strings. This cosmic web is like a three-dimensional spider web that stretches over 93 billion light years, the size of the visible universe.
With all the space and time, it makes you wonder: Do I really understand where I live?
Christopher Churchill is a Professor of Astronomy at New Mexico State University. He studies the evolution of galaxies. Email him at cwc@nmsu.edu.
This article originally appeared on Las Cruces Sun-News: Our big universe full of wonder
