Venus, Mars, Jupiter, Saturn, Uranus and Neptune, as pictured
in this composite photo, gang up on Earth to create a
Can the sun and planets line up across the solar system
and cause disaster here on Earth?
For centuries disaster and calamity have been
foretold whenever the planets of our solar system align. In
the last few decades these ideas have found their way into print
in books (making their authors good money) through predictions
about the grave consequences of such an event. The book The
Jupiter Effect predicted that California would be hit by
major earthquakes set off by an 1982 alignment. Almost two decades
later 5/5/2000: Ice, The Ultimate Disaster said that
an alignment in May of 2000 would unleash increased solar activity,
starting a chain of events that would cause the Earth's crust
to slide and poles to shift. Many of these theories suggest
that the tidal forces from these grand alignments can cause
earthquakes, floods and disasters of all sorts. What does science
tell us about these predictions? Can we associate past alignments
with catastrophes? Should we expect disasters from future alignments?
First, let's define the term alignment. An alignment
of planets and the sun, as seen from Earth, is simply a time
when many of the planets in the solar system are together in
a rough line on the other side of the sun from Earth. This would
be visible as a conjunction of the planets in the sky,
except that since the conjunction includes the sun, and the
sun washes all other light sources out of the daytime sky, it
renders the conjunction impossible to observe. Most disaster
scenarios argue that the tidal forces unleashed by an increase
in gravity in one direction will cause major problems on our
planet. Some disaster theories even have gone so far as to suggest
that the Earth might be torn in half.
Gravity is the force that pulls all objects toward
one another. The amount of gravity an object exerts is proportional
to the mass of an object. That's why a large object, like the
Earth, pulls you toward it. With a slightly smaller object,
such as the moon, there is less gravity because the moon is
only a fraction of the mass of the Earth. Even small objects,
such as you and the computer you are sitting in front of, have
gravitational pull attracting you toward each other, but because
your mass and the computer mass are so small the amount of gravity
Compared to other forces gravity is one of the
weakest in the universe, but what it does not have in strength
it makes up for in tenacity. Gravity is effective over the distance
of millions of miles between the Sun and its planets as well
as the millions of light years between the stars in a galaxy
and the billions of light years between one galaxy and another.
While gravity can act at great distances, it does lose a lot
of its strength. Every time you double the distance between
yourself and another object, the force of gravity acting on
you from that object drops by one quarter. If you put ten times
the distance between you and the other object, the strength
drops to one hundredth its original value (The strength falls
by the square of the increase in distance).
Tidal forces are caused by the gravity of one
large object acting on another. One example would be the moon's
gravity pulling on Earth. Because Earth is so big and gravity's
strength drops so rapidly with distance, the strength of the
moon's pull on the side of Earth facing it is significantly
more than the moon's pull on the far side of the Earth. This
difference acts on the Earth to try and tear it in two. Fortunately
our planet is strong enough to resist this pull. However, any
liquid material on the surface of the Earth is drawn toward
the moon by these tidal forces. That is the reason why our oceans
have low and high tides.
Under the right conditions, tidal forces can become
quite strong.. The 19th century French astronomer Édouard Roche
calculated that if a moon gets too close in its orbit around
its planet it will be torn apart by this force. Roche estimated
this distance to be about 2 1/2 times the size of the planet's
radius. This measurement had become known as the Roche Limit.
The rings around the planet Saturn are thought
to be the remains of one or more moons that came within Saturn's
Roche Limit and were shattered into the small rocks that now
compose the rings. In 1992 the comet Shoemaker-Levy 9 passed
within the Roche Limit of the planet Jupiter and was torn into
at least 21 separate pieces. Two years later these pieces plunged
into Jupiter's atmosphere in a dramatic collision that was observed
by Earth's telescopes and was broadcast around the world.
Could the Earth come to the same fate as Saturn's
moon or comet Shoemaker-Levy 9? Could an extreme planetary alignment
bring us within some interplanetary Roche Limit? Physics says,
fragments of comet Shoemaker-Levy 9 after it was torn
apart by tidal forces. Does a similar fate await Earth?
Credit: H.A. Weaver, T. E. Smith (Space
Telescope Science Institute), and NASA
While the gravity exerted by the planets Jupiter,
Saturn, Neptune and Uranus is large, they are very far away.
Thus the amount of gravity and tidal forces they exert on Earth
are only a tiny fraction of the forces our much closer moon
exerts even though the moon is much smaller. Astronomer Philip
Plait (of the Bad Astronomy
Page) has calculated the gravity and tidal forces for the
planets at their closest approach to Earth and compared them
to the same forces from the moon. According to Plait's calculations
even the largest of the planets, Jupiter, exerts only one hundredth
the force on our planet as the moon and only 0.000006 percent
of the tidal force. Venus, our nearest planetary neighbor, has
a gravity that affects us at a tiny 0.006 percent that of the
moon with tidal force of only 0.00005 percent that of the moon.
Could the combination of all the planetary forces
plus the sun and moon bring on disaster? It seems unlikely.
The gravitational forces of all the planets together add up
to less than 1.8 percent of the force of the moon (Even this
1.8 percent value is high since all the planets never get in
perfect alignment and never pull in exactly the same direction).
The moon, because its orbital path is not perfectly circular,
varies its own gravitational force on Earth as much as 25% every
two weeks with no obvious catastrophic effect on our planet.
Scientists have tried to find a connection between the tides
of the moon and earthquakes, but so far no definitive conclusions
have been reached.
Perhaps the best proof that planetary alignments
do not cause disasters can be found by simply looking at history.
Neither the 1982 alignment nor the 2000 alignment caused any
problems on our planet, though they did sell a lot of books.
So do we have to worry that an alignment of the
planets will cause some sort of disaster on Earth? No, we don't.
Planetary alignments remain a beautiful and interesting, but
safe, curiosity in the sky.
Krystek 2001. All Rights Reserved.