Our sun is one of billions and billions
just like it in the universe. It is a middle-aged, yellow, main
sequence star. Our sun is composed primarily of Hydrogen and Helium
gases. At the heart of our sun is a nuclear inferno. Our sun has been
described as a nuclear explosion being held in check by gravity. Our
sun is also very large, though its density if fairly low. If our sun
were hollow, it is estimated that one
Planet Earth's would fit inside.
Our sun is the center of our solar
system and is the source of all energy for almost every organism on
the face of the Earth. The sun provides a vast spectrum of energy.
Everyone knows that the sun produces lots of heat and light. But our
sun produces energy that is much more important. The vast amount of
energy that our sun produces is called RADIANT
ENERGY. Radiant energy is defined
as invisible and invisible light, it is also energy that travels in
waves. directly or indirectly, the sun provides nearly all of the
energy required by the organisms on Earth.
Our sun has a diameter of approximately
1.35 million kilometers. It is composed primarily of Hydrogen and
Helium. In its core, thermonuclear fusion of hydrogen is taking
place. While it is a gas, four distinct parts of the sun have been
The core is the innermost part
of our sun. It is the source of the sun's energy. The temperature of
the core is approximately 15,000,000 degrees Celsius. You may recall
that the process by which Main Sequence Stars like our sun perform to
produce energy is called Thermonuclear Fusion of Hydrogen. In
this process, Hydrogen atoms are fusted into Helium atoms by the sun's
tremendous gravity. In this process, a small amount of Hydrogen
is actually converted into lots and lots of energy. (Remember E=mc2.
about four million tons of matter is converted to energy in the sun's
core. Even at this tremendous rate of consumption, the sun has enough
fuel to continue this process for about another 5 billion
Photosphere: The photosphere is
the visible surface of the sun. When you look at the sun under normal
conditions, this is the only part that you see. It is the layer of
the sun that gives off light. It has a temperature of approximately
5,500 degrees Celsius. The photosphere also has a textured or grainy
appearance. This is primarily due to the presence of Granules (areas
on the photosphere where hotter gases rise to the surface and cooler
gases sink). The photosphere also has Sunspots, which are darker,
cooler areas on the photosphere (temp: 4,000 degrees Celsius).
sunspots are probably caused by storms in the sun's lower atmosphere.
Sunspots vary in diameter from about 16 km to 160,000 km. Sunspots
produce ions, which interfere with radio communications on Earth.
sunspots occur in approximately 1-0-12 year cycles. No-one seems to
know exactly why this is the case, but it is.
Chromosphere: The chromosphere
is the inner atmosphere of the sun. It extends several thousand
kilometers above the photosphere. The chromosphere exhibits a red
coloration due to the presence of burning hydrogen gas. The
chromosphere is much dimmer than the photosphere, and is usually
overshadowed by it. As a result, the chromosphere is only visible
during a total solar eclipse, when views of the photosphere are
blocked by Earth's moon.
The corona is the sun's upper, or
outer, atmosphere. It can extend for millions of kilometers into
space. The corona is actually a lot hotter than even the surface of
the sun and temperatures can reach into the millions of degrees
Celsius. The corona is another layer of the sun that is only visible
during a total solar eclipse. The corona also produces the Solar
Wind, which is a stream of fast-moving ions which fly from the corona
in all directions.
Features of the
The sun rotates on its axis like most
celestial objects. Since the sun is composed of gases, the sun does
not all rotate at the same rate. At its equator, the sun rotates once
in 25 Earth Days. We first learned of the sun's rotation by observing
the movement of sunspots across its surface.
Other features of our sun include
Prominences, which are large streams of gases which shoot up from the
sun and then curve back down to the surface forming great arches.
Others go millions of kilometers into space and appear as thin, dark
streaks when viewed against the sun's disc. These prominences are
called Filaments. Solar Flares are explosive increases in the
brightness of the sun, generally seen near sunspots. Flares last over
an hour and release tremendous amounts of energy. They are one source
of the particles which cause the Auroras in Earth's atmosphere.
Auroras are bands of light which result when particles from the sun
get trapped in Earth's atmosphere, causing a neon light type of
effect. Solar flares also impact Earth's communication
The Planets in our Solar
In ages past, ancient astronomers noted
that some stars seemed to move across the night sky. They termed
these special stars "wanderers", and their word for wanderer was
"Planet". We know today of course that the planets are not stars at
all. They are something entirely different. Our solar system consists
of our sun and at least nine planets that revolve around it. The
broken into two groups. Those that are closest to the sun are called
the Inner Planets. Those furthest away from the sun are called the
All of the inner planets are
Terrestrial, or Earth-like. It was long suspected that many of these
planets would harbor life of some sort. Space probes or exploratory
spacecraft have been sent in recent years to study these planets, our
closest neighbors. All of the inner planets are small and rocky, much
like our own.
With the exception of Pluto (which is
terrestrial), all of the outer planets are Gas Giants. They are much,
much different than the inner planets. They are primarily composed of
Hydrogen, Helium, Methane and Ammonia gases.
The Inner Planets
Mercury: Mercury is a small,
desolate planet. It is about 4878 km in diameter and roughly
58,000,000 kilometers from the sun. Mercury is too close to the sun
to be easily studies with telescopes from the Earth. Most of what we
know about Mercury is the result of the Mariner-10 spacecraft, which
was launched from Earth on March 2, 1978. Mariner actually went to
Mercury and set up in orbit around the small planet and radioed
information back to Earth. The surface of Mercury is similar to that
of Earth's moon. It is cry and rough and pockmarked with many
craters. Mercury has practically no atmosphere. Either the planet is
too small and therefore has too little gravity to hold an atmosphere,
or the planet is simply too close to the sun and the atmosphere
burned away many billions of years ago. Because of its effective lack
of an atmosphere, Mercury has no weather, no rain, no wind. This
means that the surface of Mercury doesn't change very much as time
passes. Recently, small amounts of what scientists believe to be ice
has been found in the shaded portions of at least some of Mercury's
craters. This frozen water is believed to have come from passing
comets. Atmospheres also tend to protect a planet from collisions
with rocks and the like from space. Since this planet doesn't have
much of an atmosphere, it doesn't get all that much protection. We
can see that Mercury's surface is literally covered with the evidence
of such collisions. When you look at the surface of Mercury, you
literally see craters, within craters, within craters. Mercury also
experiences a great change of temperature from daytime to night. In
the day, the temperature can approach 950 degrees Fahrenheit. At
night, the temperature plummets to -346 degrees
Planets as seen from Earth
Venus- Venus has been named
Earth's sister planet, since in many ways it is very much like Earth.
It is nearly the same size, mass and density as is our own planet.
Venus also comes closer to Earth than does any other planet in the
solar system. Venus is approximately 12, 104 km in diameter and about
108 million km from the sun. The surface of Venus is obscured from
our view by Venus' thick atmosphere. Droplets of sulfuric acid are
contained in clouds of carbon dioxide, giving new meaning to the term
"acid rain". This thick atmosphere also traps most of the heat energy
that strikes the planet. The process of this heat energy being
trapped by gases in the atmosphere is called the Greenhouse Effect.
As a result of this greenhouse effect, Venus experiences a constant
temperature of 900 degrees Fahrenheit. This is enough heat to melt
lead! Much of our knowledge of Venus comes from various space probes.
The Mariner series probes began with a flyby of Venus in the 1960's
and the Pioneer-Venus probe is currently in orbit and still sending
information back to Earth. Even more exciting are the reports from
the Magellan probe, which was sent to map the surface of Venus using
Radar. Because of its oppressive atmosphere, we people of Earth have
had a difficult time actually landing a space probe on the
surface. The harsh conditions within the atmosphere tends to take
its toll on our relatively fragile probes from Earth. The only
probe to ever reach the surface was the Russian space probe Valerian,
it landed and for a brief time radioed images to Earth of a strange and
alien landscape. Our vision was distorted because of the
thickness of the atmosphere, and the very landscape seemed to ripple
and waver, almost like distant stretches of a highway on a hot day here
on Earth. An interesting fact about Venus is that it experiences
Retrograde Rotation. Venus rotates in the opposite direction from the
other planets. Venus rotates backwards, or from East to West. We think
that at some point in the distant past, Venus must have experienced one
of those huge collisions that we think were relatively common back
then. This collision with some mysterious object apparently
tipped the planet completely upside down. This means that the
north pole of venus is where you would expect the south pole to
be. This little oddity is only one of the unusual things we could
expect ot witness on venus. Another interesting fact is that one
rotation of Venus on its' axis takes 243 days, one revolution around
the sun takes 225 days. This means that on Venus, a day is actually
longer than a year! Another interesting discovery about Venus is
that it is one of only three places in the solar system where there
are Active Volcanoes! This is evidence that the planet is still
an active one, and the future may well hold other changes for lovely
Infrared Venus image. Note the cloud layers.
Earth- The third planet from the
sun. A special, unique and wonderful world that we are studying for
the entire school year! Earth is approximately 150,000,000 km from
the sun and 12,756 km in diameter. Earth has one moon, called
Luna. As far as we know, Earth is the only place in the solar system
where life ever definitely developed. THAT is especially
Mars- This planet was named for
the Roman god of war. What else would be a better name for a planet
that is the color of dried blood?! Mars is about 228 million km from
the sun and about 6878 km in diameter. Ever since Giovanni
Schiaparelli observed what he thought were canals on the Martian
landscape, humans have been enamored with the idea of "little green
men on Mars". Schiaparelli saw straight lines running across the
Martian landscape and thought he was looking at canals, built by a
dying race of Martians to bring their limited supply of water from
the poles to more equatorial areas. What he actually observed were
the remains of once raging rivers, now only dry river beds. At one
time, Mars was awash with running water. Today, that water is all
gone, perhaps all contained in great polar ice caps, or contained
just below the surface of the soil in a permafrost layer. The planet
was originally explored by two famous probes, Viking I and II. One of
the Viking probes remained in orbit, sending back telemetry and
valuable data. The other Viking probe actually landed on the surface
and took samples or rocks and the like with a robotic arm. It
performed tests on the samples it collected. All of this data was
sent back to the scientists on Earth. In fact, the Viking lander is
STILL sending back data even today. Mars is tilted on its axis, so
the planet experiences seasons, much like we do here on Earth. Mars
rotates at a rate about equal to Earth, therefore the length of its
days and nights is close to what we have here on Earth. However, Mars
takes 23 months to circle the sun, so its seasons; spring, summer,
winter and fall last approximately twice as long as they on Earth.
The atmosphere of Mars is composed primarily of Carbon Dioxide and
monatomic Oxygen (O). The Viking spacecraft currently serve as
weather stations, sending back daily information. Current data
indicates that summer temperatures are around -21 degrees Fahrenheit,
and winter temperatures drop to -191 degrees Fahrenheit. This planet
has been more recently explored by the Mars Pathfinder mission. You
can find out more about this exciting, and Internet accessible,
mission, by following the link. In orbit around Mars are two, small
and lumpy satellites, named Phobos and Deimos. You may have heard
something in the news recently about a meteorite, discovered on Earth
in Antarctica, which originated on the planet Mars. The exciting
thing about this little 12 million year old piece of rock is that it
may contain evidence of past life preserved in fossil form.
Fossilized remains of a type of bacteria have been confirmed in this
sample, and there's at least a chance that this simple life form
originated on Mars! If it's true, it will be the first confirmed
example of life developing elsewhere than on our wonderful world.
Wouldn't THAT be exciting? Think of it, if in our tiny, solar
system, we know that life developed in not one, but two places, what
would that mean? Would it mean that if it could happen here it
probably happened "out there" too? Yes indeed. Tiny Mars might once
have been blessed with life at one time in the ;past, just like
Earth! Unfortunately, at some point in time, that fragile thread of
life was broken. Perhaps when Mars lost most of its atmosphere,
forever changing its climate. Still, it makes you think though,
huh? Yep, and it makes a lot of other people think as well.
Currently, NASA has a number of new missions whose focus is the tiny
red planet of Mars. Be sure to check out the Astronomy Links
section for the latest information from the Mars Rover project, as well
as other recent robotic adventures to this fascinating planet.
Olympus Mons, a large volcano on the
This image illustrates the many dried up river and stream beds
visible on the Martian surface.
An actual view of the Martian Landscape. Taken by our Viking probe
on the surface.
A view of Mars from space.
A happy crater on the Martian surface.
With the exception of Pluto, these
planets are all much larger than the inner planets. Except for Pluto,
these planets are all GAS GIANTS, composed mostly of Hydrogen
and Helium gases with smaller amounts of Methane and
JUPITER-The largest planet in our Solar
System. Jupiter contains twice the mass of the rest of the planets
combined. Jupiter is 778,300,000 km from the sun and is about 142,800
km in diameter. Jupiter rotates very quickly for a planet its size,
making a complete rotation every 10 hours! This rapid rotation has
caused the middle of the planet to become bulged outwards and the
polar regions have become flattened. Jupiter has no solid core,
though gases at its center may be compressed into the liquid state.
Jupiter's most renowned feature is the GREAT RED SPOT, a large,
cyclonic storm at Jupiter's equator. The great spot stands out
against Jupiter's brightly colored bands and can be seen easily from
Earth with a telescope. The spot is a massive storm caused by gases
rising from Jupiter's depths. You could fit about four planet Earth's
side by side, within this massive spot. Jupiter was visited by the
Voyager space probes in the 1980's. Voyager discovered a thin, faint
ring system around the planet as well as at least 23 moons. The four
largest moons were discovered in the 1650's by the famous astronomer
Galileo. These moons were first described by him and today are named
in this honor today. The GALILEAN MOONS are: Io- a small rocky and
volcanically active moon. Ganymede- a larger moon composed of rocks
and ice. Europa- a large moon that is noteworthy because it is
covered with a thick, smooth layer of ice. Large cracks have appeared
in the ice, leading to speculation for years that beneath the ice
could be found a vast ocean of some liquid. We've recently confirmed
this fact. There is a large, liquid ocean beneath the ice of Europa!
Who knows what secrets lie beneath this surface layer of ice?
Recently the GALILEO
space probe visited Jupiter and its moons, and has made some
interesting discoveries. You can get to the Galileo site by following
the link. The other GALILEAN moon of Jupiter is Callisto- a moon
which is interesting because of its pockmarked surface. There are so
many impact craters on Callisto's surface,that the moon looks sort of
like a golf ball. Callisto stands as a mute reminder of the violence
with which our solar system was born.
This is a photo of the famous Shoemaker-Levy comet about to impact
Saturn- This is the second largest
planet in our solar system and perhaps the most famous one of them
all! Saturn displays the most extensive and beautiful system of rings
that we have ever seen! Saturn is about 1,427,000,000 km from the sun
and is 120,000 km in diameter. Saturn probably has a small solid core
about the size of the Earth. Like Jupiter, Saturn rotates very
rapidly causing the poles to become flattened. Saturn's rings are its
most impressive feature. The rings are about 40,000 km wide, but only
about a kilometer or two thick. When you look at the rings edge-on,
they are barely visible. (Like looking a sheet of paper, edge-on) The
rings are composed of various particles of rocks and ice. The size of
the particles range from about 30 meters in diameter, to pebbles the
size of gravel. Saturn has at least 30 moons in addition to its ring
system. One of these moons has been particularly interesting to
scientists. Titan, one of Saturn's largest moons was studied fairly
closely by the Voyager probe. Thick, orange clouds mask its surface.
Scientists theorize that Titan may hold some clues to how life
developed first on Earth. Life may be developing on the surface of
Titan even now for all we know. We have never been able to see its
surface because of that thick cloud layer. Future space probes have
been planned to visit this fascinating moon.
An early view of Saturn's lovely rings.
Note the separations.
An infrared image of Saturn
Just beautiful, isn't it?
Uranus- Uranus is a beautiful planet
with a greenish coloration due to the presence of Methane gas. This
planet also exhibits strange rings which run " up and down", rather
than side to side, as do the rings of other planets. Uranus is
2,869,000,000 kilometers from the sun and about 51,800 kilometers in
diameter. It has ten dark rings which run from North to South and at
least 15 moons. The entire Uranian system bespeaks of the great days
of violence that preceded the development of our solar system. It's
moons have been repeatedly destroyed and reformed. A particularly
interesting moon is Miranda. Miranda is one of the coldest places in
the solar system. Here we see huge cliffs of ice, mountains laying on
their side or even upside down! Miranda was a witness to the violence
of the early days of our solar system. With further study, what
stories could Miranda tell of the origins of our solar system? Uranus
itself was once probably hit by a large comet nucleus and as a
result, is now flipped on it's side. (This is why the rings are
arranged the way they are--)
Neptune is a beautiful blue gas giant
only recently seen "up close and personal" by the Voyager probe. this
planet wasn't even discovered until 1845, and since then, has no
completed one orbit around the sun..Neptune is 4,496,000,000
kilometers from the sun and 49,5000 km in diameter. It was recently
discovered that Neptune has a large storm of the sort seen on
Jupiter. Thus, Neptune's Great Dark Spot, was named and discovered.
It is a storm very similar to the Great Red Spot on Jupiter. This large
tornado like storm would literally swallow our entire planet, it's that
big! It was
previously thought that on such a cold planet as Neptune, large
storms such as this couldn't exist, due to the extremely cold
temperatures. Neptune has at least two moons, one of which, TRITON,
is one of the largest in the solar system, temperatures there are
lower than anywhere else in our solar system.
Cloud bands on Neptune
Tiny Pluto is usually the most distant
planet in our solar system. It is also the smallest planet at just
3,000 km in diameter. Pluto is about 5,900,000,000 km from our sun.
It is a small, rocky or terrestrial world. Our sun appears as no more
than a bright star in it's sky. Because of its terrestrial nature,
Pluto is thought to be an escaped moon of Neptune, which has taken up
it's own orbit around the sun. Pluto was not discovered until around
1930. Pluto has just one moon, which is nearly as big as it is. The
moon is called CHARON, which was discovered in 1978. Charon and Pluto
are pretty much the same size, leading some scientists to call the
Pluto/Charon system a double planet, rather than a planet and a moon.
Of all the planets in our solar system, only Pluto will not be
visited by space probes by the year 2000. In fact there are no
current plans to ever send a probe to Pluto.
Planet X, Sedna and other distant
members of our Solar System
been theorized that there are more planets in our solar system out
there, in the dark reaches of space, still awaiting our
discovery. "Planet X" has long been the term given to that
"tenth" planet, still eluding our sight here on Earth. Many
scientists even dispute the fact the Pluto was classified as a planet
in the first place. These scientists propose that Pluto more on
par with an asteroid, orbiting the sun, but too small to be a planet,
and actually a member of a vast cloud of objects known to inhabit the
outer reaches of our solar system. This cluster of objects is
called Kuiper Belt, and mostly consists of fragments of ice and
rock. Perhaps Pluto, and it's moon Charon, are merely big Kuiper
Belt Objects after all. There is a fair bit of disagreement as to
exactly what the qualities of a planet should be in the first
place. To summarize, it all has to do mostly with orbits.
Objects that orbit the sun, and whose gravity has made into a spherical
object, if they are of sufficient size, and they don't share their
orbits with too many other objects, are considered a planet.
Moons are generally smaller, and usually spherical objects, but they
orbit a planet. Then, together with their planet, they also
revolve around the sun. Simple really, right? Thrown into
the mix are several areas of "rubble" in our solar system. The
first area is an asteroid belt between the orbits of Mars and
Jupiter. Most of the chunks of rock and ice in this asteroid belt
are quite a bit smaller than a planet, but they do orbit the sun.
Some are even close to the size of Pluto, but they share their orbit
with lots of other largish chunks of rock, so that disqualifies them
from "planetary status", and makes them an asteroid instead. The
Kuiper Belt begins in the the vicinity of Neptune, and has an inner
region, as well as a more distant outer region. This belt also
contains largish chunks of rocks and ice, some of which nearly as large
as Pluto, but these chunks aren't called planets because they share
their orbit with numerous similar objects, both large and small.
One such object, recently discovered, has been named Sedna. Sedna
is about 90AU's from the sun, or about 4.6 billion miles further away
from the sun than Pluto. It's about 3/4 the size of Pluto, and
may have other objects (moons) orbiting it. Many consider Sedna
to be our TENTH PLANET, others believe Sedna to be only a large Kuiper
Belt Object, and in fact, believe that's what Pluto should have been
classified in the first place. And then, way beyond tiny Sedna,
lies the realm of comets, called the Oort Cloud. Long theorized,
but never proven to actually exist. What secrets lie awaiting
discovery in this distant realm where our sun wouldn't even be the
brightest star in the sky? Time will certainly tell...
And the most beautiful planet of all...