Dr. Bozidar Mitrovic: Now the argument goes
as follows: if indeed the Earth was revolving
around the sun at a distance of one astronomical
unit, then suppose
that we have one star that is closer to us
than a group of stars
behind it.
Then we look at that star in July, it will
appear to us
to be at the left side of this cluster.
So, in July we would see it
here.
It would appear to be closest to the N star
here on the
right.
Then six months later in January, when you
view this same star
against the background of more distant stars,
then it would appear
to be closer to this star that is at the left.
Or would appear to
be here.
Basically, if indeed the earth was revolving
around the
sun, then we would see this apparent shift
in the position of
nearby stars, relative to the background of
more distant stars and
nothing like that was observed.
What is meant by a parallax is this apparent
change in the position
of an object.
In this case a nearby star due to the change
in the
location of the observer.
Actually our vision is based on parallax.
The two eyes, they actually don't give the
same view and you can
see that if you close your right eye and then
try to cover me with
the thumb, looking only through the left eye.
You don't see me
then.
But then you open the right eye and close
the left and all of
a sudden you can see me.
And the reason is that two eyes have
different viewing directions.
So what happens is our brain
processes the two images and gives us the
perception of depth.
Therefore people who do not see in one eye
they don't have a
perception of depth and for them, for instance
its difficult to
play sports.
Because if you play any sports, baseball or
football
or whatever you need that perception of depth,
so that you know
where you are in space relative to the ball.
Our vision relies on
this parallax effect, which is nothing else
but the apparent change
in the position of an object due to the change
in the position of
the observer.
OK.
So nothing like that was observed argued
Aristotle and others who supported his geocentric
view.
As a result
this idea that the earth is revolving around
the sun cannot be
correct, because if it was correct then we
would indeed see this
apparent change in the position of the stars
relative to the
background.
Of course, what they did not realize at that
time is that the stars
are much, much further away from us than what
they thought.
If they
are at a great distance, this angle here,
so called parallax angle,
is very small.
As the distance of the star increases, this
triangle
gets skinnier.
This star X angle gets smaller.
It's actually quite
small, even for the stars that are closest
to us.
It is less than
one second of arc.
Now a degree which is 360th of the full circle
is divided into
smaller units, into minutes of arc, one minute
of arc is one-
sixtieth of a degree and one second of arc
is one-sixtieth of a
minute.
That is it is 1/3600 of a degree.
To give you an idea as to
how small that angle is, it's the angle that
which you would see a
quarter, a coin, at a distance of five kilometers
from you.
If you
could see it, you can.
So is a small angle.
So even for the closest
stars, that parallax angle P is very small
and it was actually
observed for the first time in 1800s, by German
mathematician and
astronomer Bessel.
OK.
People realized earlier with essentially Galileo
that indeed this
heliocentric model is correct.
But even then we didn't have precise
enough instruments to measure such a small
angle.
So the objection
was correct but was based on the wrong assumption
that the stars
are much closer to us than they really are.
So to reproduce the diagram that I showed
you.
Here is the Sun, and
in heliocentric model the earth is revolving
around the sun.
If I
have here a nearby star and other stars in
the background, more
distant than this one here, then when the
earth is here say, in
July, it will look to me that this star is
closer to this one here.
In December it would appear that the same
star is now closer to the
one on the left.
It's one, astronomical.
The base and this angle here P is called
parallax angle.
And if the distance D to the star is very
large,
the parallax angle becomes very small and
hard to observe or
detect.
OK.
The idea of Aristarchus was kind of rejected
at that
time, although he was completely right.
Then people forgot about
it.
His writings were lost and it was introduced
much or
reintroduced much later by a Polish astronomer
Copernicus in the
16th century and he often credited for being
the first to propose
the heliocentric model.
Historians believe that he was actually aware
of the work done by
Aristarchus much earlier and he should really
be credited for
reintroducing and strongly advocating the
heliocentric model, which
at a time when he was doing that was actually
very dangerous.
You
could lose your life by proposing theories
that went against the
teachings of the Church, by the third century
AD.
Afterwards increasingly more powerful Roman
Catholic Church
accepted the teachings of Aristotle as dogma,
as something that is
given.
They argued that the Greeks came first.
They discovered it
all.
There is no point in making new discoveries,
new inquests.
All
people need to do is just inscribe the works
of Greek philosophers,
mathematicians over and over again, so they
don't get lost.
Basically the Aristotle model became frozen
in time, up until early
1500s.
