Greetings Earthlings. Before we discuss Stellar evolution and Black
Holes we must refresh our memory on basic gravity. Gravity pervades the
entire universe and it's effects are the same on Earth as they are
anywhere else in the universe. On Earth the father of Gravity was Isaac
Newton though the work of many others in the past aided Newton, such as
Johannes Kepler with his discovery that the orbit of the Planets is
elliptical not circular and his laws of Planetary Motion. Isaac Newton
was born in Woolsthorpe England on December 25, 1642 and is one of the
greatest minds to ever grace planet Earth. He is one of my Heroes and
truly launched our modern conceptions of the nature of Gravity as a
Force. When Newton was about 20 years old he went to a fair in
Stourbridge and bought a book on astrology just for fun and began to
read. He came to a diagram he did not understand so he bought a book on
trigonometry but found he could not grasp the geometric details.
Finally he bought a copy of Euclid's "Elements of Geometry." In 1666
Newton, a 23 year old undergraduate at Cambridge University, was forced
to take a year off and return to his native village, Woolsthorpe, due to
an outbreak of the Plague! During that year he invented differential and
integral calculus, made discoveries about the properties of light, and
laid the foundation for his theory of Universal Gravitation!!!!
What Newton realized was that the same force that makes an apple fall to
earth keeps the moon trapped in an orbit around the Earth. He knew the
moon would fly off into space if there were not some force pulling it
toward earth. He was the first to realize that the same force was at
work on both the apple and the moon! Newton called this Force Gravity
and using Kepler's third law of planetary motion Newton mathematically
deduced the nature of Gravitational Force. He knew the force acted over
great distances but the strength varied with distance between objects.
His law of the inverse square means simply that The gravitational force
declines inversely to the square of the distance between the objects. A
simple example is that you have two planets a known distance apart. If
you move those planets TWICE as far apart the gravity between them would
only be 1/4 as strong as before the movement. From this you can see
that the effects of gravity lessen with distance or the moon would come
crashing to earth! I think here is the proper place to answer a bright
young lady's question on the alignment of the planets and their combined
gravitational effect on each other. From Newton's inverse square law
you can see that the Sun's gravity has far more effect on the planets
than their neighbors do. When all the planets line up their
gravitational fields would be far too weak to have an effect on say the
tides of earth, however each would have more of an effect on its closest
neighbor.
A planet or any body's gravity is related to the Radius and Spin of the
body. The Radius is the distance from the center of the planet or body
to the outer crust or surface of the body. So simply put gravity is the
force that causes all objects to be attracted to each other and it's
force varies with the square of the distance between the two planets or
objects. Now you are familiar with Newtonian Gravity and realize what a
brilliant man Isaac Newton was to have deduced all this so long ago! Now
we will move on to another of my heroes Albert Einstein and discuss his
gravitational theory.
In 1905, Albert Einstein developed his theory of special relativity,
which modified Newton's theory of gravitation but gives the same
gravitational acceleration for all freely falling objects 32 ft./sec
squared. Einstein completed his general relativity theory in 1915, and
although Planetary motion had provided a particularly accurate
verification of Newton's theory, Einstein's accounted for some phenomena
in the solar system not considered by Newton. Also Einstein's theory
was more geometrical and described gravity more in relation to the
Space-Time Continuum. In Einstein's theory of General Relativity
gravity is more of a warp or dent in the Space-Time continuum.
According to his theory gravity effects all forms of matter and energy
including light as they move in space-time.
Let me pause here for a simple example of the Space-Time Continuum. It
is the same space you have always known they have just added time to it.
Remember in my first article when I told you of the closest Star to
Earth being 4.3 light years away? That means that the light you see
from that Star at night is the light that left that Star 4.3 years ago.
In other words if that Star went out suddenly, you would still see it's
light for 4.3 more years even though it is not there. So the farther
you look out into Space the farther you are looking back in time!! Now
for a simple look at Einstein's Space-Time Warp or dent. The mattress
of your bed is now the Space-Time continuum. It is flat and uniform and
undisturbed. Now we place a bowling ball in the center of the mattress
to represent planet Earth in the Space-Time continuum. You now see a
dent or warp in the flat surface of the mattress which deepens as you
approach the center of our bowling ball earth. Now in your mind's eye
you know what Einstein means by a warp in space-time. So a body (a
small rubber ball) passes by our bowling ball earth on the mattress. If
the course of the ball crosses over the warp or dent made by our bowling
ball the rubber ball will be caught in this dent and orbit the bowling
ball earth unless its forward velocity (Speed) is great enough to break
out of the dent. So all the planets orbit the Sun inside the huge dent
or warp in space-time created by the Sun. Remember the bowling ball and
mattress because you will see them again when we discuss Black Holes in
a later article.
Now back to Einstein. As I said earlier Kepler found that the orbits of
the planets were elliptical not perfect circles. However, most of the
planet orbits are very Close to circular except Mars and Mercury. Since
Mercury's orbit is an ellipse there is a part of the orbit where Mercury
comes the closest to the sun (perihelion) and a part of the orbit where
Mercury is farthest from the sun (aphelion). One of the effects
predicted by Einstein's General Relativity theory was that the elliptic
orbits of planets like Mercury would themselves rotate (or change
position) slowly in space and this phenomenon is called the advance of
perihelion. Mercury's orbit has the largest example of this effect and
it's perihelion advances 43 seconds per century. When this was
confirmed later by scientists it was considered one of the crucial tests
of the Theory of General Relativity. What this means in simple terms is
that the point along Mercury's orbit called the perihelion is simply
sliding a little further along the orbital plane to a new spot a little
further ahead and this will be the new perihelion for the next orbit
which will be in a slightly different position. More simply the orbit
of mercury remains the same in relation to the Sun but is moving
slightly in reference to the perihelion.
One of the most amazing things about Einstein is that in the period that
he wrote his Special Relativity Theory, he was working as a patent clerk
and was working on his theory in his spare time at home and work!! What
some people can do with their spare time!!!
Now for some simple gravity comparisons between the planets in the Solar
System. For our convenience we will use an average 100 pound boy and
his 15 pound dog for our subjects in this gravity comparison. The
Earth's gravity will be equal to 1.00 and the other planets gravity will
be displayed as a value more or less than Earth's Gravity.
May the Force be with you my Earthling Friends. Live Long and Prosper!
May HE whom the winds fear Light your path and Guide your steps as you
journey through this life.
Written by: The Galactic Sage
A planet or any body's gravity is related to the Radius and Spin of the body. The Radius is the distance from the center of the planet or body to the outer crust or surface of the body. So simply put gravity is the force that causes all objects to be attracted to each other and it's force varies with the square of the distance between the two planets or objects. Now you are familiar with Newtonian Gravity and realize what a brilliant man Isaac Newton was to have deduced all this so long ago! Now we will move on to another of my heroes Albert Einstein and discuss his gravitational theory.
In 1905, Albert Einstein developed his theory of special relativity, which modified Newton's theory of gravitation but gives the same gravitational acceleration for all freely falling objects 32 ft./sec squared. Einstein completed his general relativity theory in 1915, and although Planetary motion had provided a particularly accurate verification of Newton's theory, Einstein's accounted for some phenomena in the solar system not considered by Newton. Also Einstein's theory was more geometrical and described gravity more in relation to the Space-Time Continuum. In Einstein's theory of General Relativity gravity is more of a warp or dent in the Space-Time continuum. According to his theory gravity effects all forms of matter and energy including light as they move in space-time. Let me pause here for a simple example of the Space-Time Continuum. It is the same space you have always known they have just added time to it. Remember in my first article when I told you of the closest Star to Earth being 4.3 light years away? That means that the light you see from that Star at night is the light that left that Star 4.3 years ago. In other words if that Star went out suddenly, you would still see it's light for 4.3 more years even though it is not there. So the farther you look out into Space the farther you are looking back in time!! Now for a simple look at Einstein's Space-Time Warp or dent. The mattress of your bed is now the Space-Time continuum. It is flat and uniform and undisturbed. Now we place a bowling ball in the center of the mattress to represent planet Earth in the Space-Time continuum. You now see a dent or warp in the flat surface of the mattress which deepens as you approach the center of our bowling ball earth. Now in your mind's eye you know what Einstein means by a warp in space-time. So a body (a small rubber ball) passes by our bowling ball earth on the mattress. If the course of the ball crosses over the warp or dent made by our bowling ball the rubber ball will be caught in this dent and orbit the bowling ball earth unless its forward velocity (Speed) is great enough to break out of the dent. So all the planets orbit the Sun inside the huge dent or warp in space-time created by the Sun. Remember the bowling ball and mattress because you will see them again when we discuss Black Holes in a later article.
