Download Orbit by Tega Jessa Everything in the universe circles or “orbits

Orbit
by Tega Jessa
Everything in the universe circles or “orbits”
something else. It’s true for meteors and planets,
stars and galaxies. They’re all under the
influence of each other, moving in an ageless
and eternal dance. So what exactly is is orbit?
What causes this phenomenon? And why is it so
important to spaceflight and space exploration?
In this article I’ll try to briefly answer these
questions.
First of all, orbit is the circular – or more
accurately – ovoid path of an object around a
center of mass. As we all learn in high school
physics, Force equals mass times acceleration.
When a mass changes speed and direction
(which is acceleration), it produces a force. The
main expression of this force in space is gravity.
Gravity is the pull of every object in existence
on each other. The bigger the difference between
two objects in proximity to each other, the
greater the force of gravity between them. This
is why a person is held to the ground by the
gravitational force of the much more massive
Earth. This is true for any two objects with a
similar mass ratio. The only way to escape the
gravitational pull of a massive object is to have
considerable mass yourself and or move at a
high speed. If you were to give a short
explanation of why orbits happen it would be
that an object isn’t massive enough and or fast
enough to most escape the gravitational pull of
its center of mass.
Orbit happens as an object is able to normally
have enough mass and speed to avoid the pull of
gravity from the much larger object near it. If we
are to use the Earth as example we find out why.
Say you launched a baseball into the air. Under
normal circumstances the ball will quickly fall
back to the ground. But what happens if you
were to throw the ball higher? It would still fall
but take longer depending on how high it is.
However if you were to throw the ball fast
enough and high enough it would go into orbit.
That is because as an object goes in a straight
line at a fast enough speed past a planet, the
gravity of that planet pulls on the object. This
create the object’s orbit. Another good example
is a ball on a string being swung by a child. As
long as the child pulls on the string while
swinging the ball it goes in a circle, but when the
child lets go the ball goes in a straight line.
Orbit is important to space flight for several
reasons. First, the observation of orbit gave
aeronautics the principles that helps space craft
escape the earth’s atmosphere. Second, several
instruments and craft used by spaceflight rely on
the use of orbits in one way or another. So as
you can see orbit are very important for a lot of
reasons.
Gravity in Space
by Tega Jessa
One of the big challenges to long term travel in
space is gravity. We now know that other than
radiation and the cold vacuum of space, the
biggest threat to a person’s health is lack of
gravity. The human body was developed to
thrive under the force of gravity. This is why our
muscular and skeletal systems are shaped the
way they are. Over time, in a zero g or
weightless environment, the bones of the body
become brittle and certain muscles, like those in
the thigh actually weaken. There are also
worries about its effect on the circulatory system
as well
Planetary Orbits
by John Carl Villanueva
So if a voyage with the latest propulsion
technology to Mars takes 11 months or more
coming and going, there is a concern that the
long amount of time in space might have even
more detrimental effects, like making it
impossible for astronauts to safely return to
Earth.
So scientist and even science fiction writers have
been thinking about how to create gravity in
space. There are several proposals some already
proven and others that are still theory. The first
is to us the centripetal force of a rotating hull.
This is method is the most trustworthy as the
effect has been observed on Earth. Every object
in the universe wants to go in a straight line. In
the case of planets, its the pull of gravity from an
object with great mass that curves most celestial
object’s paths. In the case of a space craft it
would be the hull itself. Since you can’t walk
through solid walls the force of your body
wanting to go in a straight line would resemble
gravity.
This theory has drawbacks. First, the amount of
gravity you feel would vary depending on how
close you are to the center of the craft. Scientists
believe that the longer the radius of the
spacecraft the less the effect will be felt. The
other challenge is nausea. You are still basically
on something like a huge merry go round. Like
on its namesake, some people will be able to
handle it and others will experience nausea. But
in most cases its believed that if if the space
craft rotates at 1 rotation per minute the nausea
won’t be an issue.
The other method of maintaining gravity is to
constantly accelerate a spacecraft at 9.8 m/s,
Earth’s acceleration due to gravity. The problem
with this is that due to limitations imposed by
fuel there is no spacecraft that can maintain this
rate of acceleration more than 7 minutes. This
idea might become possible if a more reliable
source of propulsion is found.
Planets in a star system move around their
mother star in their planetary orbits. Most of
these orbits are elliptical, i.e., shaped as an
ellipse. That means, while it may be possible for
some planets to follow a circular path (since a
circle is just a special kind of ellipse) around
their mother star, most of them do not.
The deviation of the planets‘orbital path from a
perfect circle, which is measured in terms of a
parameter known as eccentricity, is normally not
large though. Eccentricity values of elliptical
orbital paths range from zero (the eccentricity of
a perfect circle) to 1.
In our Solar System, Mercury has the largest
eccentricity (most deviated from a perfect circle)
at 0.2056. Interestingly, its adjacent neighbor,
Venus, has the lowest eccentricity at 0.0068.
Had scientists not demoted Pluto from being
planet, it would have had the highest eccentricity
at 0.249. In case you’re interested, Earth‘s
eccentricity is 0.0167.
Eccentricity plays a role in the determining the
amount of heat a planet gets from its mother
star. A planet gets its lowest amount of sunlight
at its aphelion.
There was a time when the Earth, not the Sun,
was believed to be the center of the Solar
System (in fact, also of the Universe). This idea
was known as the geocentric model. It was so
well-embraced, that many ancient Greek
astronomers, including Plato, Aristotle and
Ptolemy, subscribed to it. The idea existed as far
back as 6th century BC, and prevailed in
teachings of astronomy for a long time.
In fact, it was not until the mid 1500′s that a well
presented argument against the geocentric model
was introduced. The opposing theory was
proposed by Nicolaus Copernicus and gave
mankind its first taste of heliocentric cosmology,
the view that the Sun was the center about which
other celestial bodies orbited.
About half a century later, Johannes Kepler
composed his three laws of planetary motion.
The first stated that, “The orbit of every planet is
an ellipse, with the Sun at a focus.” The second
stated that, “A line joining a planet and the Sun
sweeps out equal areas in equal times.” Finally,
the third stated that, “The square of the orbital
period of a planet is proportional to the cube of
the semi-major axis of its orbit.”
On that same century, in 1687, Isaac Newton
formulated his law of universal gravitation,
which talked about the force that held the
planets in their planetary orbits. The most recent
prominent contribution to the theories governing
planetary orbits is Einstein’s general theory of
relativity, which explains gravity in the context
of spatio-temporal curvature.
Eccentricity
by Jean Tate
When it comes to space, the word eccentricity
nearly always refers to orbital eccentricity, or
the eccentricity of the orbit of an astronomical
body, like a planet, star, or moon. In turn, this
relies on a mathematical description, or
summary, of the body’s orbit, assuming
Newtonian gravity (or something very close to
it). Such orbits are approximately elliptical in
shape, and a key parameter describing the ellipse
is its eccentricity.
In simple terms, a circular orbit has an
eccentricity of zero, and a parabolic or radial
orbit an eccentricity of 1 (if the orbit is
hyperbolic, its eccentricity is greater than 1); of
course, if the eccentricity is 1 or greater, the
‘orbit’ is a bit of a misnomer!
In a planetary system with more than one planet
(or for a planet with more than one moon, or a
multiple star system other than a binary), orbits
are only approximately elliptical, because each
planet has a gravitational pull on every other
one, and these accelerations produce nonelliptical orbits. And modeling orbits assuming
the theory of general relativity describes gravity
also leads to orbits which are only
approximately elliptical (this is particular so for
binary pulsars).
Nonetheless, orbits are nearly always
summarized as ellipses, with eccentricity as one
of the key orbital parameters. Why? Because
this is very convenient, and because deviations
from ellipses can be easily described by small
perturbations.
The formula for eccentricity, in a two-body
system under Newtonian gravity, is relatively
easy to write, but, unfortunately, beyond the
capabilities of the HTML coding of this
webpage.
However, if you know the maximum distance of
a body, from the center of mass – the apoapsis
(apohelion, for solar system planets), ra – and
the minimum such distance – the periapsis
(perihelion), rp – then the eccentricity, e, of the
orbit is just:
E = (ra – rp)/( ra+ rp)
Weight on Other
Planets
by Abby Cessna
Many children, and even adults, dream of
visiting other planets and wonder what it would
be like to stand on another planet. For one thing,
your weight would be different on another
planet, depending on a number of factors
including the mass of the planet and how far you
are away from the center of the planet.
Before we start, it’s important to understand that
the kilogram is actually a measurement of your
mass. And your mass doesn’t change when you
go anywhere in the Universe and experience
different amounts of gravity. Your weight is best
measured in newtons. But since your bathroom
doesn’t measure your weight in newtons, we’ll
use kilograms. This is what your bathroom scale
would say if you stepped on another world.
Mercury is the smallest planet in our Solar
System, but it is dense. Because Mercury is so
small, it has very little gravity. If you weighed
68 kg on Earth, you would only weigh 25.7 kg
on Mercury.
Venus is very close to Earth in size and mass.
Venus’ mass is roughly 90% of the mass of the
Earth. Thus, it is no surprise that someone would
weigh a similar amount on Venus. Someone
who weighed 68 kg on Earth would weigh 61.6
kg on Venus.
Mars is quite a bit smaller than Earth with only
11% of our planet‘s mass. Mars is larger than
Mercury, but it is not as dense as the smaller
planet. If you weighed 68 kg on Earth then you
would weigh 25.6 kg on Mars. Since Pluto was
demoted to a dwarf planet, Mars became the
planet where you would weigh the least.
Jupiter is the largest planet in our Solar System
with the most mass. Because of Jupiter’s mass,
you would weigh more on that planet than on
any other one in our Solar System. If you
weighed 68 kg on Earth then you would weigh
160.7 kg on Jupiter, over twice your normal
weight. That is if you could actually stand on
Jupiter’s surface, which is impossible because it
is a gas giant, and gas giants do not have solid
surfaces.
Saturn is a gas giant best known for its planetary
rings system. It is also the second biggest planet
in our Solar System. Despite its mass though,
the planet has a very low density and a lower
gravity than Earth. If you weighed 68 kg on
Earth, you would weigh 72.3 kg on Saturn.
Uranus is a gas giant without a solid surface.
Although Uranus is larger in size than Neptune,
it has less mass and therefore less gravity. You
would only weigh 60.4 kg on Uranus, if you
weighed 68 kg on Earth.
Neptune, the last planet in our Solar System, is a
gas giant. If you weighed 68 kg on Earth, then
you would weigh 76.5 kg on Neptune if you
could stand on the planet’s surface.
Although the Moon is not a planet, it is one of
the few objects that astronauts have actually
visited. Because the Moon is so small, it has a
low density and low gravity. If you weighed 68
kg on Earth, then you would only weigh 11.2 kg
on the Moon.