Thrawn Rickle 78HOW BIG IS BIG?© 2004 Williscroft 

A
lightyear is the distance light travels in a year. The numbers get so big that
they lose meaning, so let’s set up a mental picture we can understand. In
one second, a beam of light would travel around the Earth about seven and a
half times, and since the circumference of the Earth is about 24,900 miles,
this means that light travels approximately 7½ x 24,900 = 186,000 miles in a
second (in round figures). That calculates to just under 670 million miles in
an hour; which converts to just under 16.1 billion (thousand million) miles in
a day; which converts to somewhat over 5.8 trillion (million million) miles in
a year, so a lightyear is equal to 5.8 million million miles. That
didn’t help much did it? Look
at it this way. Light takes about nine minutes to arrive at the Earth from the
sun. It takes about 9 years to arrive at the Earth from Sirius, so Sirius is
about 526 million times further from the Earth than is our own sun. That
probably helps a bit, but it still is insufficient to get a clear mental
picture. Let’s
try one final analogy. Place a basketball at the goal posts of a football
field. The Earth would be a pea a foot away. Jupiter would be an orange at
about the two yard line, Pluto—the “edge” of our solar system—would be
a speck near the thirteen yard line, and Sirius would appear as two balls 106
miles away, one about twentyfive percent larger than our sun and a pea
about the size of the Earth. These
are relationships we can actually understand. While
we’re at it, let’s place more of our universe into this picture. The
galaxy in which our sun and all its planet’s resides is about 100,000
lightyears across. In the picture we have developed with the basketball and
the football field, our galaxy is one million miles across, or about four
times the actual distance between the Earth and the Moon. And the Andromeda
Nebula, which is the closest large galaxy to our own, and about two million
lightyears from our galaxy, would be 20 million miles away from our
basketball, or about one fifth the actual distance to our sun. The
distances get so large so fast, that it is nearly impossible to keep a
relative picture in mind of how all this relates together. If we collapse our
example so that the entire galaxy, which in our example extended to four times
the distance to the Moon, shrinks to the size of a Frisbee, then Andromeda
will be another Frisbee at about the seven yard line. We are part of
about 13 galaxies in a sphere ten million lightyears across—in our collapsed
example about forty yards across. Let’s
transfer our base of operations to the fiftyyard line so we can better
visualize what we have: In a twenty yard sphere centered at the middle of the
fiftyyard line, we have some thirteen Frisbees of various sizes, in various
orientations. Now imagine a sphere that extends outward four and a half
football fields in all directions from center field, a sphere nearly 900 yards
across—approaching a mile in diameter. This sphere in our collapsed example
represents the Virgo Supercluster containing our Local Group of thirteen
galaxies plus 160 or so other clusters of galaxies. Time
to collapse again; this is still too big to contemplate. So we collapse our
milewide supercluster down to basketball size again, which represents a
distance of about 200 million lightyears. Within a sphere extending three
yards out, that is a sphere six yards across, we will find about eighty other
superclusters similar to our own Virgo Supercluster. This sphere that is now
six yards across represents a billion (thousand million) lightyears. Now,
if you extend the current sphere so that it takes in the entire football field
and the bleachers, this represents on our scale, the size of the known
universe, about twentyeight billion lightyears across. These
numbers get so large so quickly, that it is nearly impossible not to get lost
contemplating them. We started out with a basketball representing our sun, and
discovered that the Sirius star system was over a hundred miles away, and our
galaxy extended four times the distance to the Moon. The nearest other galaxy
was one fifth the distance to the sun. So we collapsed our galaxy to a Frisbee
and located us inside a fortyyard sphere; this Local Group was but a part of
the Virgo Supercluster inside a milewide sphere. So we collapsed again to
basketball size, and found our supercluster part of 160 other superclusters in
a sixyard sphere. Finally, we extended our sphere to include the bleachers
and beyond, to contain the entire known universe. So how big is big?

