Written Expressions 3rd Year Classes
Collected by GUELLIL MABROUK (mgbay13.com)
Unit Five: Are we alone?
Topic64:
Most people looking at the night sky may think that they see “falling stars” which are actually meteors or
comets. Discuss the difference between a meteor and a comet.
Typical Essay:
There are quite a few objects in the universe capable of causing a really, really bad day on planet Earth,
including a wayward cometor large asteroid . Most meteors, however, barely rate a 'ho-hum' on an astronomer's scale of
scary extraterrestrial events. There are a number of differences between a cometand a meteor, from their
general composition to the roles they play in the universe.
A cometis a celestial object believed to be composed primarily of space dust and frozen gases. The birthplace
of a cometis thought to be somewhere in the outer parts of the universe, not related to the formation of our
solar system at all. A cometfollows an orbit that may bring it close to a star, such as our own Sun. As the
cometapproaches the star, a portion of its ice core may melt and release a trail of dust-sized particles. This cycle
can continue for millions of years.
A meteor, on the other hand, does not follow an orbit around the sun. It isn't even called a meteor while it
remains floating in outer space - it's called a meteoroid. Only when it enters the Earth's atmosphere is it
considered a true meteor.
When the Earth passes through a comettrail or debris field, individual meteoroids hit or skip across the first
layers of the atmosphere. Observers on Earth may be fortunate enough to see the last few seconds of a meteor's
existence as it streaks across the sky and burns up. Unlike a comet, a meteor will not return a number of years
later.
A cometrarely passes within a few million miles of the Earth, while a meteor by its very definition must strike
the first layers of the Earth's atmosphere. A comet's arrival can be predicted with some degree of accuracy, but
a meteor can enter the Earth's atmosphere at any time of the day or night. A cometcan rarely be seen by the
naked eye, but during a HYPERLINK "http://www.wisegeek.com/what-is-a-meteor-shower.htm" meteor shower, it is not unusual to see dozens or even hundreds of meteors within a
few hours.
A cometalso receives an official name for identification, such as Swift-Tuttle, Hale-Bopp or Halley's Comet. A
few large asteroids may receive identifying names as well, but meteors do not. Virtually all meteors cease to
exist once they've entered the Earth's atmosphere. A rare few make it to the ground, however. Once a meteor
has made contact with the Earth's surface, it becomes known as a meteorite. While a cometmay be composed
of space dust, organic materials and ice, most meteors contain elemental metals, such as iron, along with
inorganic minerals such as HYPERLINK "http://www.wisegeek.com/what-is-quartz.htm" quartz.
Topic65:
Cosmologists and astronomers predicted an expanding universe. Discuss.
Typical Essay:
Ever since HYPERLINK "http://www.wisegeek.com/who-was-albert-einstein.htm" Einstein's HYPERLINK "http://www.wisegeek.com/what-is-a-theory.htm" theory of HYPERLINK "http://www.wisegeek.com/what-is-general-relativity.htm" general relativity was applied to what is known about the universe as a whole,
it has been suspected that the universe was expanding. When Edwin Hubble and Milton Humason discovered
in the 1920s that practically all galaxies in the sky were moving away from us at great speeds, this boosted
suspicions that the universe was expanding at a rapid rate. Yet it was not until 2000 that decisive evidence was
finally found in favor of the universe's expansion, in the form of extensive redshift surveys of very distant
objects.
The expanding universe is often cited as the most significant finding in modern HYPERLINK "http://www.wisegeek.com/what-is-cosmology.htm" cosmology. In Einstein's time,
the steady-state theory was the predominant one, which stated that the universe remained balanced at the
same size. Einstein, whose equations predicted universal expansion or contraction but not stasis, artificially
introduced a stabilizing variable into his equations, called the "cosmological constant." After realizing from
Hubble's observations that the universe was likely expanding, he later called this his "greatest blunder."
The phenomenon that first led cosmologists and astronomers to predict an expanding universe was Hubble's
analysis of redshift. Using the Mount Wilson Observatory, which was the best telescope in the world at the
time, Hubble viewed distant galaxies and saw they looked progressively redde. He looked further away in
space, and by extension, further back in time as well, as light takes many billions of years to travel from these
galaxies to Earth. Because the redness factor correlated so well with increases in distance, Hubble suspected this
was a reliable phenomenon with a physical cause.
The cause was determined to be as follows: as the universe expands, the underlying space increases in volume,
but the light traveling through it remains the same. The expanding space stretches out the wavelength of the
light, making it longer and thereby redder. An analogy sometimes used is dots on the surface of an expanding
balloon. Draw a wave pattern on a balloon, and while you blow it up, notice how the wave stretches out and
becomes longer. This is the same principle behind the phenomenon of redshift.
In 1998, it was discovered not only that the universe is expanding, but that it is likely expanding at an
accelerating rate. The physical reason for this is chalked up to a mysterious "HYPERLINK "http://www.wisegeek.com/what-is-dark-energy.htm" dark energy," so named because
we barely know a thing about it.
Topic66:
Satellites facilitated space research. Discuss what a satellite is.
Typical Essay:
A satellite can be defined as any object, either manmade or naturally occurring, that orbits around something
else. For example, the moon orbits around Earth and is thus a satellite. The Earth orbits around the sun and is a
satellite of the sun. Other examples of naturally occurring satellites include HYPERLINK "http://www.wisegeek.com/what-is-a-comet.htm" comets, stars, asteroids, and other
planets.
Orbit is determined by the gravitational pull of the object around which the satellite circles. The thing around
which a satellite circles is called the primary object. However, primary objects are also affected by their
satellites, and feel some of their gravitational pull. In some cases, when two objects have a similar size and
weight (mass), and a similar gravitational pull, they may be called HYPERLINK "http://www.wisegeek.com/what-is-binary.htm" binary systems, rather than being called a
primary object and a satellite. Some argue that Pluto’s moon HYPERLINK "http://www.wisegeek.com/in-greek-mythology-who-is-charon.htm" Charon, and Pluto, represent a binary system
instead of a primary object and satellite, since both have similar mass.
Most are more familiar with the term satellite in relationship to the many satellites that circulate the earth.
HYPERLINK "http://www.wisegeek.com/what-is-sputnik.htm" Sputnik was the first artificial satellite, launched in 1957 by the Soviet Union. The launching of Sputnik is
almost analogous for the beginning of the HYPERLINK "http://www.wisegeek.com/what-was-the-space-race.htm" Space Race that followed between the US and the USSR. In today’s
climate, however, many countries have found that a cooperative effort is more successful in space exploration
and studies. The International Space Station, a satellite that orbits earth, is currently the largest manmade
satellite in Space, and represents the cooperative effort of numerous countries.
Manmade satellites are classified by types, and there are over ten types. Some of the main types of satellite
used today include astronomical satellites, communication satellites, earth observation satellites, weather
satellites and space stations. Other types of satellites include those used to monitor earth from a military
standpoint, and biosatellites, which may carry animals or other lifeforms for the purpose of research on earth
lifeforms in space. Navigational satellites are now popular and form a vital part of the HYPERLINK "http://www.wisegeek.com/what-is-gps.htm" global positioning
system (HYPERLINK "http://www.wisegeek.com/what-is-gps.htm" GPS) now available in many cars.
Satellites may also be classified by the height at which they orbit earth or another body. A low earth orbit
circles the earth at a height of 0-1240 miles (1995.59 km). High earth orbits can be as far away as 22,240 miles
(35,791.81 km). Medium earth orbits represent the distance in between high and low earth orbits. Further
distinctions exist to describe the type of orbit a manmade or natural satellite has. For example, Pluto has a
slightly elliptical orbit. Also a satellite is often classed by what primary object it orbits. A satellite that circles the
Earth has a geocentric orbit, for example. The earth, and the planets in our solar system are classed as having a
heliocentric orbit since they circle the sun.
A manmade satellite can serve many purposes. We currently use many different types of satellite systems to
track things like weather, to make our cellphones work, to find out how to get somewhere and to gather more
information about earth, and about the HYPERLINK "http://www.wisegeek.com/what-is-a-galaxy.htm" galaxy. About 5000 manmade satellites currently orbit earth, and on
clear dark nights, it’s often possible to see one in the night sky. Of course, viewing a planet, the stars, or comets
is also viewing a satellite. We also must remember, we live on a satellite, and are not stationary in the sky.
Topic67:
The National Aeronautics and Space Administration (NASA) contributed much to astronomy. Discuss.
Typical Essay:
The National Aeronautics and Space Administration (NASA) is an American government agency which runs
the civilian arm of the space program. The aim of NASA is to increase human understanding of the solar
system and the universe that contains it, and to improve American aeronautics ability. Under its charter,
NASA is supposed to be a peacetime agency that does not perform military functions, although NASA does
cooperate with the military, and many NASA employees have a military background. To achieve this goal,
NASA has an annual budget which can be counted in the billions to fund programs and pay tens of thousands
of employees.
NASA was founded in 1958, in response to the Soviet launch of HYPERLINK "http://www.wisegeek.com/what-is-sputnik.htm" Sputnik in 1957. The early years of the
organization were driven by HYPERLINK "http://www.wisegeek.com/what-was-the-cold-war.htm" Cold War competitiveness, and NASA quickly worked on creating rockets which
would allow for manned spaceflight. NASA astronauts HYPERLINK "http://www.wisegeek.com/who-is-neil-armstrong.htm" Neil Armstrong and Buzz Aldrin were the first humans
known to have set foot on the moon in 1969, an action that was considered a major victory for American
aeronautics. Riding on this early success, NASA continued development of aeronautic equipment designed to
function outside the Earth's atmosphere.
After the moon landing, NASA focused on doing research around the solar system, sending an assortment of
manned flights to the moon to collect material for study, and unmanned drones to other planets to collect data.
These flights have collected large amounts of data which are constantly being added to and analyzed. Scientific
advancement is a large part of NASA's mission. With the assistance of the agency, scientists have been able to
conduct experiments in the zero HYPERLINK "http://www.wisegeek.com/what-is-gravity.htm" gravity environment of space, and test hypotheses about the universe.
NASA also continues to work on a HYPERLINK "http://www.wisegeek.com/what-is-a-space-shuttle.htm" space shuttle program to make space more accessible. As of 2007, the
space shuttle had made 112 flights with astronauts from many nations including the United States, and two of
these flights, the Challenger and Columbia, were lost. NASA plans to HYPERLINK "http://www.wisegeek.com/what-is-a-resume.htm" resume manned flights to the moon by
2020, after safety improvements have been made to the space shuttle.
As part of its mission as a peaceful agency, NASA cooperates with agencies within the United States and
international aeronautics agencies. A NASA HYPERLINK "http://www.wisegeek.com/what-is-an-astronaut.htm" astronaut can usually be found on board the International Space
Station, and astronauts from other nations are invited to participate in NASA events. This fostering of
international cooperation will hopefully continue as humans explore space and the possibility of off-Earth
human settlements becomes possible.
Topic68:
Cosmologists and astronomers predicted an expanding universe. Discuss.
Typical Essay:
Space travel is a form of travel in which passengers enter space, the vast region outside the protective envelope
of the Earth's atmosphere. Space starts 62 miles (100 kilometers) above the Earth's crust, at a point called the
Karman Line, and it continues for a distance which appears to be infinite, interrupted periodically by celestial
bodies such as stars, planets, and so forth. Humans have long had romantic associations with space travel, with
people considering space “the final frontier,” as they famously say on Star Trek.
Humans have been intrigued by the night sky for centuries, tracking the movements of stars, planets, HYPERLINK "http://www.wisegeek.com/what-is-a-comet.htm" comets,
and other features in the sky and pondering the mysteries of the heavens. In the 20th century, the fascination
with space took on a whole new level of excitement when humans successfully launched manned spacecraft
out of the Earth's atmosphere, putting astronauts in space and on the Moon. With the proof that manned
spaceflight was possible, the concept of space travel began to seem less like a HYPERLINK "http://www.wisegeek.com/what-is-a-pipe-dream.htm" pipe dream and more like a
reality, and private companies began to enter the field, developing space planes and offering commercial
flights.
In the 20th century, space travel was restricted to astronauts who worked for various governments, and it was
primarily performed for research purposes. Space travel allowed people to collect samples from the Moon,
maintain space telescopes such as the Hubble Telescope, and eventually to perform research on the
International Space Station, a structure which orbits the Earth and houses astronauts from several nations at
any given time.
While space travel for research is certainly admirable and important, many people are more interested in the
potential for space travel as a form of recreation, tourism, or exploration. Civilians began purchasing tickets for
tourist flights into space in the early 2000s, sometimes going on brief suborbital flights in which they barely
entered space, and sometimes spending several days in space, exploring the International Space Station and
enjoying the experience of being in space.
The potential for space travel is infinite, just like the universe, bounded only by human technology. Many
people hope that the dreams of science fiction, such as massive ships which can travel between galaxies, will
someday be realized. Space travel could be used to explore the rest of the solar system and HYPERLINK "http://www.wisegeek.com/what-is-a-galaxy.htm" galaxy, learning
more about the nature of the universe and potentially leading to a discovery of life beyond the boundaries of
Earth
Topic69:
We are living in a universe still being discovered. Discuss how big our universe is.
Typical Essay:
The current, observable universe has been determined to have a width of 156 billion light years, with an error
of less than 1%, by the latest deep-space telescope WMAP. At first, it might seem impossible that scientists are
so sure of this astronomical measurement, but this figure has been narrowed by years of research and
determined by several paths of inquiry. Also, the size of the universe is intimately dependent on its shape, age,
acceleration, and total mass, so we are very confident in this figure.
In 2003, the Wilkinson Microwave Anisotropy Probe sent back enough data for scientists to publish extremely
dependable studies that established two previously unknown facts about the universe. They determined our
universe is flat, which means standard Euclidean geometry is valid on the largest scale. This can be understood
by saying a straight line more or less stays a straight line for as long as it extends. They also established that the
universe is accelerating at an ever-increasing rate, which means that all mass is flying away from each other at
faster and faster speeds. The WMAP data measured the temperature, called the cosmic microwave background
radiation, of our observable universe with an unprecedented accuracy, to within a 5% error. From these facts,
we can deduce figures such as the radius of the universe.
Remember that the size of the universe is not a constant value, nor is it the size of an object as we traditionally
understand it. The size of the universe is actually the size of space itself, and as space expands, so does the space
between planets, stars, and galaxies. At the beginning of the universe, the Big Bang created space and time as
we know them. From that moment, space has been expanding, so we find its size by measuring how far light
could have traveled since the Big Bang, along with how much space itself stretched.
We can only possibly look or communicate up to the edge, or "horizon," of where light has traveled since the
beginning of the universe. The size of the universe means the space in which we can interact with anything. We
will never ever know what is "beyond" this boundary, because there is no way to know anything about it, so
it's illogical to consider the realm "outside" of our universe, or to wonder what we are expanding "into."
An independent measure of the size of our universe can be given by studying the oldest stars. The oldest stars
we have found are probably somewhere between 11 and 14 billion light years old. If we had stars older than
the largest distance light could have traveled, then we'd know there was something wrong with our
calculations; there would not be enough time for them to evolve. However, these values are consistent with
everything else we know about the universe.
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