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View Full Version : Appreciation of Cosmic Distances



Maddad
2005-Feb-01, 10:03 AM
This post may be too basic for Bad Bob's forum, but it is still impressive to remember the scale of the universe.
It is so difficult to launch men into orbit that so far only the United States, Russia, and very recently China have done so. All of us have seen the breathtaking videos of astronauts floating 400 kilometers up near the space station as the blue marble of Earth turned below. However, many of us had not yet been born when we sent men a thousand times further to the Moon. The fact that nobody has ever duplicated that feat, even 35 years later, underscores the difficulty of that achievement.

Some people feel that going just a little bit further from the Moon bring us to Mars. The Red Planet at its closest though is well more than a hundred times further away from us than the Moon is. Comparing the distance to the Space Station and to Mars is similar to comparing the distance across your fingernail to a kilometer.

In class, we mentioned the definition of a lightyear, but we really did not appreciate its meaning. Light moves so fast it would zip around the world seven times in a second, and yet it must travel an entire year at that pace to cover that lightyear. Stellar distances are so vast that light would travel for four years to reach our nearest neighbor Proxima Centauri. This is 750,000 times as far away as Mars, and yet many people think of Mars as the next stepping-stone to the stars.

Proxima Centauri is just the nearest star, so other stars in our galaxy are vastly further yet. The stars on the far side of our galaxy are perhaps 20,000 times as far as our nearest stellar neighbor. When ET phones home from there, he has to wait for 160,000 years before finding out if anyone picked up the receiver.

As unthinkably vast as the distance across our galaxy is, we are not done quite yet. We have other galaxies. The closest one, Andromeda, sits 2 million light years away or 25 times as far away as the furthest star in our own galaxy. Andromeda is the closest galaxy to us, but others are further. The most distant galaxies that we can see are more than 5,000 times further from us than Andromeda. The light from these objects started their journey to us long before our sun and earth existed.

Since we see them from all the way across the observable universe, we also see them as they were more than 10 billion years ago, not as they are now. Expanding space was then rushing away from us at nearly the speed of light. In the intervening years, they have continued to move away from us at an ever-accelerating pace. Although we will never be able to measure their distance from us, we estimate that these most distant objects are now perhaps ten times further away, about 150 billion light years from where we are now.

The universe is a very big place.

cyswxman
2005-Feb-01, 10:09 AM
Somehow the Total Perspective Vortex comes to mind. :o

Normandy6644
2005-Feb-01, 04:26 PM
I've seen bigger!

:lol:

joema
2005-Feb-01, 05:21 PM
...we also see them as they were more than 10 billion years ago, not as they are now. Expanding space was then rushing away from us at nearly the speed of light. In the intervening years, they have continued to move away from us at an ever-accelerating pace. Although we will never be able to measure their distance from us, we estimate that these most distant objects are now perhaps ten times further away, about 150 billion light years from where we are now....
I believe the farthest objects are more like 28 billion light years away (comoving radial distance). The distances can be confusing. Here's a good thread on the subject:

http://www.badastronomy.com/phpBB/viewtopic.php?p=53334&highlight=#53334

Philippe
2005-Feb-01, 05:37 PM
Somehow the Total Perspective Vortex comes to mind. :o

Yes, but with a cup of tea, it'll go down real nice.

Nick
2005-Feb-01, 07:58 PM
I use 'Celestia' here on Linux (truly superb program) and moving at a few 100,000 miles an hour really brings home how BIG the whole thing is... you actually don't appear to be moving at all.

This is a _must have_ program too:

http://sourceforge.net/projects/celestia/

Nick

Tacitus
2005-Feb-01, 08:03 PM
Somehow the Total Perspective Vortex comes to mind. :o

It works, unless you're first name is Zaphod :)

Ilya
2005-Feb-02, 04:03 AM
My favorite illustration of cosmic distances:

Imagine Solar System so shrunk that the distance between Sun and Earth is an inch. At that scale Sun is a barely visible spark of light and Earth is microscopic, as are all planets. Jupiter is five inches away, and almost every object ever sent into space by human beings spent its entire existence inside that 10-inch diameter circle, taking months or years getting to its destination. Neptune and Pluto are 2.5 feet away, and Pioneer and Voyager probes, the farthest ambassodors of humanity as of now, are 6-7 feet away -- and took about 30 years to get there.

On that scale, a light-year is a MILE.

Maddad
2005-Feb-02, 04:25 AM
And on that scale the Andromeda galaxy, the very closest one to us, would be a trip around the world.

80 times.