Download Where is the edge of the solar system?

Sunday Daily Nation Lifestyle Mag.
Date: 31.08.2014
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Where is the edge of the solar system?
DEAR READERS, some of the
questions that I get are quite
straightforward. They leave me
wondering why you are asking
instead of simply doing the calcu­
lation for yourself.
Someone recently asked me
how many telephone num­
bers can be accommodated in
one prefix code. say. 0733. Ifs
easy: we can only get 0733­
000000. 0733­000001. 0733­
solar system" really refer to? That
is not a simple problem. In fact,
therefore, travelling at one billion
kilometres per hour, sunlight
astronomers have never defined
it! However, common sense tells
takes about 4.5 hours to reach
But I must insist that the orbit
where the sun ceases to be the
of Neptune is not the edge of the
solar system. There are thousands
dominant object.
There are many ways of de­
termining whether the sun is the
dominant object. We may say it is
brightest star (that is, it looks just
999999. You don't have to count
like the other stars); or where its
gravity is no longer the greatest
force; or even where its magnetic
field becomes insignificant.
But I suspect that when most
people talk about "the edge of
the sofar system", they mean the
exactly one million possible num­
bers. I am yet to figure out why
this reader asked that question.
Another reader asked this
seemingly simple question: "How
long would it take for light to
travel from the edge of the solar
system to earth?" Now the speed
of light is known; it is 299,792,458
metres per second ­ this is usually
rounded off to 300,000km/s.
But since we are more ac­
customed to kilometres per
of heavenly bodies existing far
beyond this planet and they all
have orbits around the sun. So
they are part of the solar system.
the point where the sun is not the
000002....0733­841451....0733­
them to know that there are
Neptune.
us that this should be the place
The farthest known so far is
Sedna, Its orbit extends as far as
77 billion kilometres from the sun.
Sunlight takes over three days to
get there. But this Is still not the
edge of the solar system!
orbit of the farthest planet.
Unfortunately, that is also
not straightforward. It depends
on when you went to school!
Between 1930 and 1979, Pluto
was the farthest planet; then, on
February 1979, it swapped places
with Neptune.
That situation continued for 20
hour, the speed of light in these
units comes to approximately
one billion kilometres per hour.
Therefore, if we can get distance
to the edge of the solar system
in billions of kilometres, it will be
easy to work out how many hours
a beam of light would take to
traverse it.
But what does "the edge of the
years until February 1999 when
Pluto again became the farthest
planet. But a more dramatic
change came in 2006 when as­
tronomers agreed that Pluto is
not actually a planet! So, as of
today, the farthest planet is Nep­
tune. It is approximately 4.5 bil­
lion kilometres from the sun and
The solar system.
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