"asger" wrote in message ...
Hi,
am new to astronomy, and was wondering, what do you define universe
as?
thanks,
asger
'Lo Asger --
I define our Universe as being unimaginably huge and
chock full of interesting mysteries and puzzles!
For most of human history people defined the Universe
as a place where Earth was at its center and everything
in the sky traveled around the Earth. It's easy to see why
because anything else seems counter-intuitive.
Almost 2 thousand years ago a guy named Ptolemy
even proved the above using mathematics!
Then about 450 years ago a man who is called "The
Founder of Modern Astronomy," Nikolas Copernicus,
used mathematics to show that Ptolemy had been
wrong for all those many years. Copernicus was able
to show that the Sun was the center of the Universe...
that Earth and everything else revolved around our Sun.
Yet it would be an average lifetime before this idea
would even begin to "catch on!"
So for a little less than 300 years, the Universe was
defined as "heliocentric" or "Sun-centered." In the year
1920, an astronomer named Harlow Shapley was able
to begin convincing people that, while some of the
objects in the sky went around the Sun, many of them
did not. Shapley believed that our Sun along with many
other stars traveled around the center of the Universe.
In fact, up until about the mid-1920s, everything in the
sky was believed to be inside our Milky Way Galaxy.
And Shapley showed that our Sun was very far away
from the center of the galaxy.
A word i like to use to describe this is "galaxocentric"
(although Shapley's mental picture of the Universe did
not last long enough to even be officially named). So
it went something like this...
Aristotle/Ptolemy_____"geocentric" or Earth-centered
Copernicus_________"heliocentric" or Sun-centered
Shapley________"galaxocentric" or Galaxy-centered
Then another great astronomer, Edwin Hubble, was
able to show in the mid-1920s that our Milky Way
Galaxy was just one of many galaxies, each galaxy
home to a great many stars!
To continue your journey and to see why i define the
Universe as i do, check out the speed of light. As you
may already know, the light from the stars and other
objects in the sky travels to our eyes at a finite speed
of about 300 million meters per second. Or if you like,
about 186 thousand miles per second.
This means that the reflected light from our Moon takes
about a second-and-a-half to reach us. The planet Mars
also reflects the Sun's light, yet even when it's closest to
us (like it was recently) the light from Mars takes a little
over 3 minutes to get to Earth.
And the light from our Sun reaches us in a little more
than 8 minutes. It takes over 4 years for the light from
the next nearest star to reach us. And if light could get
through the great dust cloud, it would take it around 30
thousand years to get to us from the center of our
galaxy!
Our galaxy is so large that it takes about 100 thousand
years for light to travel from one edge, through the
middle, and back out to the other edge.
The *nearest* big galaxy to ours, the Andromeda Galaxy,
is so far away that it takes more than 2 million years for
the light from its stars to reach us. And some of the
objects that scientists have seen with telescopes are so
far away that their light rays zoom through space for many
billions of years before we see them!
Since pictures can say it even better than words, you are
invited to go to the following website to get a better idea
about how astronomers presently define the Universe...
http://www.anzwers.org/free/universe/index.html
And most important of all... always remember, Asger, that
YOU ARE WHO YOU ARE! While sometimes the Universe
can make a person feel smaller than a pea, a growing love
for astronomy can make you feel larger than life!
happy days and...
starry starry nights!
--
A smidgeon of fear and a sprinkle of strife
And a whole lotta love till your cold...
Most everyone here wants to live a long life,
Ah! but nobody wants to get old.
Paine Ellsworth