Astronomy
The study of the Universe
The science of Astronomy has developed over time to include studying the objects found in space, and to the development of theories attempting to explain how everything began.
People have been looking at space for a long, long time. The concept of what we think of as space took a long time to develop.
Ancient peoples used the stars for many things.
The image on the previous slide was the constellation of the little bear (part of which is the little dipper). This image helps illustrate two of the things ancient people used the stars for.
One was to help tell stories. The big and little bears were part of some Native American stories that helped explain why the leaves change color in the fall.
The other use of stars was navigation. The tip of the little bears’ tail is the North Star. Since the North Star always appears to hover over the the center of Earth’s North pole it never rises or sets. Since it is always North it can be used it as a guide or reference.
Another way ancient people used the stars, sun and moon was to create calendars. Some used structures (such as Stonehenge above) to mark days or special events. When the sun rose over a particular part of a building or structure it would mark an important day or event.
They could also use the sun to tell time (hour of the day). They used the moon to tell the month. Full moon to full moon would mark the passing of a month.
History of Astronomy
For most of human history man has pictured himself and the Earth as the center of the universe. Every bright object in the sky (the sun, moon and stars) seem to circle the planet. If you stand in one spot for 48 hours you would see a parade of objects in the sky that pass over head moving from East to West. The sun “rises” moves overhead and ‘sets”. The moon follows a similar path, as do the stars.
Here is an image of stars moving made by leaving a camera’s shutter open for a long period of time.
This perception of all objects spinning around the Earth fed creation stories that always placed man at the center of the universe. This includes the explanation of the creation of the universe in the Old Testament of the Bible. God creates the Earth and the rest of the Universe in six days, placing man in the center.
During the period we consider to be the birth of modern science in Europe the Catholic church was extremely powerful. The bible was viewed to be the absolute truth (as many still consider it to be). To speak against what it said was considered blasphemy, and punishable by death.
Around 1513 A.D. a Polish scientist named Nicolaus Copernicus developed a theory that challenged the long held belief that the earth was the center of the Universe. He developed the idea while studying in Rome. He used mathematics to show that some of the larger objects in the sky orbited the sun. In 1540 someone convinced Copernicus to publish his theory. He died in 1543 (supposedly receiving a copy of his book on his death bed). In his theory Copernicus placed the sun at the center of the Universe and gave everything else circular orbits around the sun.
While Copernicus’ theory was incorrect ( the sun is not stationary at the center of the universe, and the planet’s orbits are not circular) his theory shifted the focus of scientists to a way of perceiving the universe that was closer to how it actually is (not Earth centered).
During the 1600s Galileo Galilei became convinced that Copernicus’ theory was correct. His belief was further cemented through letters with a German mathematician and astronomer Johannes Kepler. Kepler developed mathematical formulas that changed the circular orbits of Copernicus’ theory to elliptical orbits. These formulas worked and allowed the prediction of planets locations in the sky. This proved that they were orbiting the sun, not the Earth.
Galileo also used his telescope to observe the objects in the night sky. He was able to observe the Milky Way and it’s abundance of stars. He also discovered four moons orbiting Jupiter. These were the first objects ever discovered that orbited something other than the Earth. These observations, combined with Kepler’s mathematical formulas convinced him that Copernicus was correct.
Galileo’s theories became public through his lectures, letters and papers. His theories about a sun centered universe came to the attention of the Catholic Church. An investigation was started into the ramifications of Galileo’s theories, and how they related to the church’s views. The Inquisition that had been appointed decided that the theories proposed by Galileo were threatening to the church’s beliefs. He was summoned to a meeting with the Inquisition and he was told not to discuss the Copernican system or teach it in any way. This caused Galileo to stop teaching or writing about the Copernican theory. Many years passed and a new Pope was elected. Galileo was encouraged to publish his findings relating to the Copernican theory by a high ranking member of the Catholic Church under the approval of the new Pope. The book is published and was well received by the scientific communities of the time.
It was not as well received by some of the Bishops of the Catholic Church who had been involved with insisting on the original charges against Galileo (This would make a great mini series on T.V.). Under pressure from these Bishops, the Pope (who had approved allowing Galileo to publish his book) orders Galileo to stand trial. There is a lot of controversy surrounding the trial and the evidence against Galileo, you can read more by following the “Trial link” below. In the end he is forced to renounce his theories and placed under house arrest in the home of the Arch Bishop of Sienna. Galileo is eventually allowed to return to his home (still under house arrest) and dies in 1641.
Although Galileo was forced to renounce his book and theories, they were out there being read and discussed. As a result the scientific community began to work with these new concepts and build on them.
Another scientist began to develop many theories that helped explain some of the observed phenomena that scientists could not understand, such as the elliptical orbits of the planets. This scientist/ mathematician was Isaac Newton, who developed both the Laws of Motion and the Theory of Gravity (amongst others and the mathematics of trigonometry)
Newton went to college in Cambridge England. While there he became very interested in the field of mathematics, in particular Geometry (causing him to abandon his pursuit of science). While there he developed his mathematical proofs of his theory of gravity, calculating the moon’s movement using it’s (incorrectly) calculated distance and speed, and the masses of the moon and Earth. While his calculations did not work exactly (due to the errors in the calculated distance) they were close enough to convince him the Earth’s gravity affected objects to at least the moon’s distance. He also calculated the rate of gravity’s affects as distance increased. He published a book called Principia outlining all this in 1686.
Newton’s diagram showing the geometry of moon fall
Although Principia was published in 1686, Newton had started developing his theories 20 years earlier. Through the 20 year course of mathematically trying to prove his theory of gravity he also developed his theories related to motion. He released these theories in the same year, 1686. They helped explain the motions observed in space, and some of the irregularities in the gravitational mathematics.
For more information follow the following links.
Newton’s �Laws of Motion
Before we discuss Newton’s Laws of Motion, we should probably look at the concept of force. In its simplest definition, force is a push or pull on an object. A more complex way to look at it, is a force is anything that changes the state of an object’s motion. On one of the web sites linked from the previous page Force was described in the mathematical equation f=ma. In this equation ”f” represents force, “m” represents mass and “a” represents acceleration. Using this formula we can compare how an objects mass affects the force it will apply to another object.
f= ma
A related concept is momentum. Momentum is the force carried by an object. Its formula is p=mv, where p equals the objects momentum, m equals the objects mass and v equals the objects velocity (which is its speed).
p=mv
Since we mentioned Momentum, let’s look at the concept of Inertia. Inertia is an object’s resistance to change in motion. Many times this is associated with an object at rest, and the term Momentum is associated with an object in motion. However in the truest sense, inertia is the resistance of any object, at rest or in motion, to change its motion. So if we had a box that weighed one hundred pounds, it would take a specific amount of force to start it in motion. Once we had it moving it would take less force to keep it moving, because it would have a resistance to change its motion, which is now moving.
An object’s inertia is strongly related to its mass. If the box in the example above weighed ten pounds it would take much less force to start it moving because its inertia would be less. This is the same with a moving object. As we already saw in slide 20 the mathematical formula to define momentum (a moving objects inertia) is M=mv. That is why it takes less distance for a compact car to stop than a large truck, if both are going the same speed at the time force is applied to stop them.
Let us take some time and look at Newton’s Laws of Motion. They are broken into three separate laws. If you looked at either of the links on the previous page, you might have found the wording of the laws confusing. I am going to try to explain them using simpler terms.
I will break the First Law of Motion into two parts:
An object a rest tends to stay at rest until acted upon by an outside force.
An object in motion tends to stay in motion, in a straight line and at a constant speed, until acted upon by an outside force.
To restate this, if an object is sitting somewhere, it will remain in that spot until some sort of force is applied to it. If you went outside and picked up a rock, brought it inside and set it on a shelf, it would remain there until some force caused it to move.
Now if you took that same rock and hit it with your hand it would move. That makes sense, the part of Newton’s First Law that does not make sense to most people is that it will move in a straight line at a constant speed until acted upon by an outside force. On the shelf we could probably picture friction slowing down and stopping the rock. It is harder to truly imagine anything traveling in a straight line forever, because we have never experienced this first hand. No matter how hard we throw something it always hits the ground within sight. That is what amazes me about Newton. He was able to picture this in an age before flight, let alone space flight. Even with our society’s familiarity with space through satellites and probes that have flown to distant planets, it is hard for most people to picture them moving in a straight line, at a constant speed until acted upon by an outside force such as gravity.
Newton’s Second Law of Motion states that the change of an object’s motion is proportional, and in the direction, to the force applied to that object. So if an object has a force applied to it, its motion will change. How much that motion changes depends on the amount of force, and direction of force that is applied. Let’s say a car is driving down a straight road. A golf ball comes flying from the passenger side of the car at 60 miles an hour, and hits the car. The cars motion will change very little. This is because the mass of the golf ball is so little that its force is also small. A mile down the road a car comes at the exact same angle as the golf ball, and the same speed as the golf ball, and hits the first car (car A). This time car A’s motion and direction of motion will change dramatically. This is because car B’s force is much greater than the golf ball, because its mass is much greater.
Newton’s Third Law of Motion states that for every force (action) there is an equal and opposite force (action). This is probably the most famous of the three laws, though most people use it inappropriately. In the example from the previous law the golf ball and the car experienced the exact same force, in opposite directions. If the golf ball applied ten pounds of force to the car door, the car door applied ten pounds of force back onto the golf ball in the opposite direction. This is why a gun kicks, the expansion of the ignited gun powder puts equal pressure on the bullet forcing it one direction, and the gun forcing it the other direction. It is also why a rocket works in space. The force created by the rocket’s engine igniting fuel and forcing it out a small space at the back of the engine, forces the rocket to move in the opposite direction, even if the gas has nothing to push on.
Gravity
Gravity- While gravity was discussed and theorized about a long time before Newton, he is generally credited with its discovery (we have all heard the old apple on Newton’s head story). What Newton did, was develop a theory on what gravity was, and worked out a mathematical formula to explain his observations. He published this theory in Principia. In his theory gravity is a force of attraction, between objects with mass. Any object with mass exerts a force on other objects around it. The amount of force is proportional to the mass of the object, and its distance to the other object. The greater the mass, the more gravitational force an object applies. The closer objects are to each other the greater the force applied. As objects get further apart the amount of gravitational force experienced between the two objects decreases. Newton’s Universal Law of Gravitation is written as:
F=G(m1m2/r2)
Where F= Gravitational Force, G= a universal constant, m is the mass of object one and object 2 and r is the distance between the centers of both masses.
Let us look at an example to try to understand this more clearly. If we look at the earth and our moon we will hopefully be able to picture how this works. Since both of these objects have mass they both exert a gravitational force on the other. The Earth has more mass than the moon. This means that it exerts a greater force on the moon than the moon exerts on the Earth.
The Earth’s gravitational pull is strong enough to keep the moon from continuing in a straight line out in to space (as we learned would happen with Newton’s laws of motion). If the moon had a different mass, or a different velocity (speed) it would be a different distance from Earth than it is now. For example if the moon had less mass, it would need to be closer to the Earth. That is because with less mass, the attraction force between the Earth and moon would decrease (remember Newton’s formula is based on the mass of the two objects), this would allow the moon to continue on a straight line out into space.
This goes for any object in space that orbits another object. The distance from each other is dependent on the two objects masses, and the speed of the object that orbits the other. That is because a moving object has inertia which must be factored in as part of its mass. Examples would be a sun and its planets, a planet and its moon(s). The key idea is the two objects masses and the distance from each other determines the gravitational force exerted on each other.
Einstein changed how scientists look at gravity. In Einstein’s General Theory of Relativity he proposed that what we experience as gravity is the result of a curvature in space time. In his theory Einstein proposes that time is a fourth dimension of space, in addition to length, width and height. To picture this imagine that space is a piece of graph paper. Every thing in the universe is located between the grid lines on the front and back of the paper. An object deforms the grids as it moves through the plane of space time (through the paper). This causes a curvature in the grid. The more mass an object has, the greater the curve in the paper. The greater the curve in space/time, the greater the object’s gravitational effect.
An often used example is the mesh of a trampoline. The heavier the object on the trampoline, the more the mesh bends. If we put a marble on the mesh it will be drawn to the object in the center. The heavier the object in the center, the greater the distance the bend it creates will affect the marble. This is illustrated in the image above. Of course you would have to have an identical mesh, deformed the same way on top of the sphere.
This is how Einstein’s theory applies to space. The more mass an object has the greater its affect on the space around it. The more mass the greater its gravitational effect, or influence. If an object has enough speed it can maintain an orbit around the bend in space time surrounding a more massive object. Since there is no friction in space the orbiting object can maintain its orbit.
For most students (well most people actually) it is easier to picture and understand Newton’s explanation of Gravity. It is easier to imagine, or picture an object creating a force that attracts other things to it. Probably because of our experience with magnets attracting each other, or metal objects. However it is Einstein’s theory that is currently accepted. Below is a chart that will hopefully help compare the two theories.
If you trip space pushes you to the ground.
If you trip gravity pulls you to the ground
The fabric of space pushes objects towards the object that has bent the fabric with its mass
An object’s gravitational force pulls things towards the center of the object
Object’s mass bends the fabric of space, the more mass the more dramatic the bend
Object’s mass creates force, more mass more force
Einstein
Newton
As our technologies have improved and increased what we can see and learn about the Universe that surrounds our tiny planet, our understandings and theories about the Universe have changed. That is what is so exciting about Astronomy now. New information about the Universe is coming faster than scientists can analyze it. This has led to an explosion of discoveries and theories that are helping us to better understand the universe and our own planet.
We will now start to look at our own solar system, and then move out to the rest of the universe. We will look at what scientists think they know about space, the technologies scientists use to increase their knowledge, and the current theories used to explain what is out there and how it all started.
Our Solar System
The Sun- Our sun is a star. It is not a large star, nor it is it a small star. It is an average sized star that is about half way through it’s estimated life span of 10 billion years. It formed like any other star, from a nebula of gas (mostly hydrogen) and other heavier chemicals left over from previous star’s supernovas (we will go into this in more depth later). The planets formed from heavier elements and particles that formed a disk around the ball of gas that became our sun.
Mercury- The first planet out from the sun and the smallest.
It has the shortest year, due to it’s close proximity to the sun.
It has very little atmosphere so is subject to extreme temperature variations. The side facing the sun gets extremely hot, while the side away from the sun cools off to a very low temperature.
It’s rocky cratered surface resembles that of our own moon.
Venus- The second planet out and often called Earth’s sister planet. This is because both Earth and Venus are very similar in size and density. This is where the similarities end.
It has the hottest average temperature of any planet in the solar system due to a greenhouse effect created by its thick sulfuric atmosphere
The only planet whose day is longer than it’s year, that means it takes longer to complete one rotation on its axis than it does to orbit the sun
Spins on it’s axis in the opposite direction of all the other planets.
Earth- Our home planet. The only planet known to have life.
Has three main layers- Core, Mantle, Crust (As do Venus and Mars)
The core is theorized to be solid Iron. The Iron atoms are aligned in one direction due to the huge pressure in the center of the Earth. This creates a magnetic field that helps protect the Earth.
The atmosphere is composed of 78% Nitrogen, 21% Oxygen and 1% other gasses.
Mars- Considered to be the most like Earth in terms of its composition and potential for life to have started
Its red color reminded early astronomers of the color of blood, leading them to name it after the Roman god of war
The red color is created by large amounts of Iron Oxide (rust) in the soil
Has polar ice caps composed of frozen Carbon Dioxide
Recent probes to Mars has discovered signs that water once existed on the planet
The Asteroid Belt- This is found between the orbits of Mars and Jupiter. It is an area of small objects ranging from pebbles to the state of Texas in size. They are rocky objects that are believed to be left over from the formation of the solar system. The gravitational effects of Jupiter and Mars help keep the asteroids in their circular orbit. At times asteroids impacting each other can cause one to leave the “belt”. Scientists believe that this is how Mars got its moons (as well as the moons of many other planets). Asteroid strikes have also been blamed for the major extinctions that have occurred on Earth.
Jupiter- The largest planet in the Solar System
It could hold more than a thousand Earths inside of it
Generates twice the amount of heat energy that it receives from the sun
It has the fastest rotation speed of all the planets
Jupiter’s core is theorized to either be rocky, or a liquid. The theory goes back and forth between the two. It is most recently back to the rocky core theory
The Giant Red Spot has been in existence since at least Galileo’s time. It is a giant storm that circles the planet
It has 3 rings
Saturn- The ringed planet. Though it is not the only planet with rings, it is the one best known for that characteristic.
Has the lowest density of any planet (lower than water)
It has three main rings which are contain thousands of smaller ringlets
The rings are composed of ice and dust
It also generates more heat than it receives from the sun
Its high rotational speed, coupled with its low density cause it to bulge at the equator
Uranus- The planet on its side. It is called this because its axis is 90 degrees to its orbit
It has 11 rings
It is bluish in color due to the Methane in its outer atmosphere
Neptune- The smallest of the gas giants
Its atmosphere also contains large amounts of Methane
It has four rings
It also has storms (like Jupiter’s) that often appear
Planet
Day
Year
Mercury
56.65 Earth Days
87.97 Earth Days
Venus
243 Earth Days
224.7 Earth Days
Earth
23.96 Earth Hours
365.26 Earth Days
Mars
24.37 Earth Hours
687 Earth Days
Jupiter
9.8 Earth Hours
11.86 Earth Years
Saturn
10.20 Earth Hours
24.46 Earth Years
Uranus
17.90 Earth Hours
83.75 Earth Years
Neptune
19.10 Earth Hours
163.72 Earth Years
It is interesting to compare the length of each planet’s day and year. It is estimated that when Earth first formed 4.5 Billion years ago its day length was around six hours.
Dwarf Planets
Big changes in 2006
In the summer of 2006 the International Astronomical Union voted on a resolution to change the definition of a planet. It was a tumultuous gathering, with several proposals thrown out and argued over. The first reports were that the Union had decided to base the definition of a planet on two criteria. One was to set a minimum size, based on diameter. The other was the object’s mass being large enough to cause it to form into a sphere. This originally added three new planets, Charon (Pluto’s moon), Ceres ( a large asteroid in the Asteroid belt) and Xena (officially 2003 UB313), a large object found in the Oort cloud).
Suddenly that all changed. The Union voted to adopt a resolution that defined a planet on more than just diameter and its formation into a spherical shape. The new definition required the astronomical body to have enough gravity to “have cleared the neighborhood around its orbit ”.
IAU/Lars Holm Nielsen
This second vote not only took Charon, Ceres and Xena back off the planet list, it also removed Pluto. These objects are now all defined as Dwarf Planets.
Below is an image of the vote taking place on one of the resolutions.
IAU/Lars Holm Nielsen
So the new definition of a planet has several parts:
1) Is in orbit around the sun
2) Has enough mass that its gravity caused it to form as a sphere
3) Has cleared the neighborhood around its orbit
It is number three that has caused Pluto’s planetary status to be changed. So far my research has indicated that since it passes through a portion of the Kuiper Belt, ( a disk of large icy objects beyond Neptune’s orbit) and has not pushed the Kuiper belt objects further out away from the Sun, it is not considered to have cleared the neighborhood around its orbit.
According to the new resolution a Dwarf Planet is a celestial body that
A) is in orbit around the Sun
B) has sufficient mass to form as a sphere
C) has not cleared the neighborhood around its orbit
D) is not a satellite ( a satellite is a body that orbits a planet, whether man made or natural)
This is the definition that Pluto now falls under. Originally (during the conference) it was announced that Charon (Pluto’s largest moon) was going to considered a Dwarf Planet. This changed during the conference because the debate switched to keep it as a satellite of Pluto. The debatable piece of this is whether Pluto and Charon are Binary Dwarf Planets. This is because of Charon’s size and mass when compared to Pluto. Because Charon’s mass is so large Charon does not orbit Pluto. Rather Pluto and Charon orbit a point part way between them. So the IAU needs to decide if this makes them Binary Dwarf Planets or keep Charon as a satellite of Pluto
Pluto- Was the smallest of the original planets (discovered in 1930)
It is composed primarily of rock and frozen water
It is theorized that it did not form when the other planets did, but rather is a Kuiper Belt (a large belt of rocky, icy objects beyond Neptune’s orbit)that was captured by the sun’s gravity
Its orbit is extremely elliptical, causing it to loop within Neptune’s orbital distance, allowing it to be closer the sun than Neptune for fourteen years.
It is orbited by Charon, which is almost as large as Pluto (though two possible moons, known as Nix and Hydra, have recently been discovered).
Charon- Currently considered to be a moon of Pluto
It is half the size of Pluto
Its mass is so great that Charon and Pluto orbit a barycenter ( a location part way between the two objects)
An artist’s representation of Pluto and Charon
Ceres- Recently upgraded to the status of a Dwarf Planet
When it was discovered in 1801 it was originally classified as a planet.
Later it was downgraded to an asteroid.
It is located in the asteroid belt between Mars and Jupiter
Eris- The largest known Dwarf Planet, slightly larger than Pluto
Until September 13 2006 it was known as 2003 UB313- Xena
Is a Kuiper Belt object with a large orbit (three times greater at its farthest distance from the sun than Pluto’s greatest distance from the sun)
For an interesting look at Eris’ unique orbit check out
The Moon
Earth’s Moon- Any object that orbits a planet is a satellite. Therefore all moons are satellites. Since we call our satellite “The Moon”, when other planets were found to have satellites we also called them moons (though modern astronomers generally stick with calling them satellites). When someone refers to ”The Moon” they are referring to our satellite.
It is believed that our moon formed when a large object slammed into the Earth early in it’s formation. The early solar system was full of objects clumping together from the remnants of the cloud of gas and dust that formed the sun. It was a time of lots of collisions between these objects. Scientists believe a very large object struck the Earth causing it to eject a lot of material into space. This material had enough mass to reform into a sphere that became the Moon.
The Earth/ Moon relationship is very interesting compared to the moons of the other planets. Our moon is massive compared to the other moons of the solar system (particularly when you compare it to the size of the planet it orbits).
Only Three of Jupiter’s moons, and Saturn’s moon Titan are larger than our moon.
The moon’s mass creates a gravitational pull on the Earth. This pull causes the earth’s surface to flex. This flexing causes the ocean tides we experience. It is also theorized to have effects on geologic occurrences such as earthquakes and volcanic eruptions.
Another interesting aspect of the Earth / Moon relationship is that the same side of the moon always faces the Earth. It takes the exact same time for the Moon to spin once on its axis as it does for it to complete one full orbit of the Earth. This cycle takes 29.5 days to complete.
Although we call the side of the moon we never see “the dark side” of the moon, it does not actually remain dark. When we experience the moon as a “new moon”, meaning it is dark to our view, the side we can not see is in full sunlight.
As long as I have mentioned the ‘new moon”, let us talk about why we see different phases of the moon. We have all seen and heard of the “full moon”, “quarter moon”, “crescent moon” and “new moon”. Many people don’t know why we see the different phases, or why we can see the moon at different times of the day.
Most people think of the moon as rising when the sun sets , and setting when the sun rises. While this does happen, it only happens one day out of the moon’s 29.5 day cycle. Since the Earth spins on its axis every 24 hours, and the moon takes 29.5 days to orbit the Earth, it appears in the sky at a different time each day. The moon rises when the sun sets during it’s “full moon” phase. The following day it rises approximately 50 minutes later, and is slightly less than full. Each day the time the moon appears in the sky is approximately 50 minutes later than the previous day. The apparent shape of the moon changes each day as well. This is because the moon’s relation to the Sun and Earth changes slightly each day. The slight change of angle the “lighted” side of the moon is viewed from changes its viewed shape.
This illustration helps show the moon in various locations during its orbit around Earth. Since it only reflects light from the sun we can only see the portion of the moon pointed towards the sun. Since our angle of view changes each day, we see the different phases of the moon.
Sun
Northern Lights
The Northern Lights- While we are discussing Earth/ Space relations let us look at the Northern Lights (or Aurora Borealis). This is a phenomena that occurs at the two poles (called the Southern Aurora in the Southern Hemisphere). It all starts when the Sun has an eruption of energy called a solar flare. These solar flares(shown in the images to the left) send out huge amounts of energy into space. This energy contains charged particles that travel to the Earth over the period of a couple of days.
In the picture on the previous page we saw the Earth represented with a magnet in its center. Since the Earth’s core is composed of solid iron, with the atoms oriented to create a magnetic field, this picture is not far from the truth. The lines coming out from the magnet represent the magnetic field generated by the core (all magnets generate this type of field). This magnetic field that surrounds the Earth is called the magnetosphere.
The magnetosphere protects the Earth from much of the harmful energy arriving from the sun. The bands of magnetic energy deflect some of the “solar wind” (what scientists call the flow of energy from the sun). In the case of the Northern Lights some of the charged particles released by the solar flare travel along the magnetosphere and are drawn in at the poles. As the charged particles enter the atmosphere they strike gas molecules. The solar particle’s energy is transferred to the gas molecule and re-released as light energy. Different gases release different wavelengths of light. Oxygen releases red, Nitrogen green.
Photo by Erik Olsen
The farther North or South from the equator you go the more common and spectacular the light show is. We often see dim white bands of the Northern Lights here. Every so often we get a spectacular show (such as in 2003) here in Midcoast Maine.
Meteors
Meteors- Meteors are another phenomena that occur in the Earth’s atmosphere. A meteor is a streak of light that crosses the sky. The light is created when an object enters the Earth’s atmosphere and heats up as it strikes gas molecules in the atmosphere (actually it is compressing and heating the atmospheric gas). There are many objects that can cause this to occur.
There are three basic terms associated with Meteors. Let’s define these three terms.
Meteor- The object that makes the flash of light that streaks across the sky.
Meteorite- The object left over after entering the atmosphere.
Most meteors disintegrate during their passage through the atmosphere. Those that make it, and fall to Earth as meteorites are classed by their chemical make up.
Most meteors have a stony or stony /iron composition. The majority come from the remnants of asteroids. A few have been linked to the Moon or Mars. Scientists believe that past collisions of large asteroids ejected matter from these two planetary objects. These pieces of Mars and the Moon eventually made into the Earth’s atmosphere.
Stony/iron type
Mars or Moon origin type
Meteor showers are periods when up to 100 meteors an hour are visible. They are created by another type of space debris. Meteor showers occur when the Earth passes through the debris left by a comet. Two of the most famous are the Leonid meteor shower, which occurs in November, and the Perseid meteor shower which occurs in August. The debris that creates the meteors in these showers are generally very small, the size of a dust particle.
On the opposite end of the spectrum, large asteroids would also be considered a meteor once they entered our atmosphere. But instead of disintegrating as they move through the atmosphere they could cause major damage and destruction, such as the one theorized to have caused the extinction of the dinosaurs.
This is an image of the Barringer Crater, the result of the impact of a 30-50 meter asteroid. It is 1200 M across and 200 M deep
Asteroids
Asteroids- Asteroids are objects found in our Solar System. They are believed to be objects left over from the disk of matter that formed the planets. The majority are found in a belt located between Jupiter and Mars. They are objects that are a combination of ice and rock. Many of Jupiter’s outer moons, as well as both of Mars’ moons are thought to be captured asteroids.
Comets
Comets- Comets are objects that scientists think come from the Oort cloud. They are composed of mostly ice (in the form of frozen gasses) and dust. They orbit the sun in very large elliptical orbits.
This is an image of the comet Hale-Bopp. It has an orbital period calculated to be 4026 years.
This is an image of the comet Kohoutek. As in the image of Hale-Bopp you can see that the comet appears to be a bright ball with two tails shooting off behind it.
A comet is composed of several parts. The main body of the comet is called the Nucleus.
It is the object that was theoretically bumped into motion and left the Oort cloud. As it approaches the sun in its orbit it begins to become heated by the solar wind. This causes the frozen gasses and dust to heat up and be released from the nucleus. This aura of gas and dust near the nucleus is called the Coma.
As the dust and gas is released the solar wind carries it away from the Head (nucleus and coma combined) of the comet. This creates an interesting optical illusion for humans viewing the comet. We assume that the comet’s tail would be like the flame of a rocket, or exhaust of a plane. That the tail would flow behind the motion of the comet. This is not the case. The tail flows away from the sun, and does not necessarily point the direction the comet is moving.
The tail of the comet reflects the light of the sun. The comet below Ikeya-Seki is not necessarily heading towards the East (the picture was taken at dawn). Rather that is the direction of the sun. �The dust left from the tail remains in space after the comet has moved on. As we learned in the meteor section this dust can cause meteor showers if the earth passes through it on it’s orbit around the sun.
While it looks like a comet is streaking across the sky, it has little apparent motion as you look at it. Rather it appears as a stationary object in the sky, like the stars around and behind it. Over the course of several days it moves across the night sky and disappears.
Balls of gas ice and dust from outside the solar system (Oort cloud). They orbit the sun in large elliptical orbits. Give off a “tail” as they come close to the sun.
Comets
Rocky, icy objects found in a belt between Mars and Jupiter. Believed to be left over from the formation of the solar system
Asteroids
Object that enters earth’s atmosphere, and heats up giving off a flash of light that moves across the sky
Meteor
Galaxies
Galaxies- Galaxies are large clusters of stars. Scientists are still working to figure out how they form. There are several different types, such as Spiral, Irregular, Elliptical and Lenticular. They contain Billions to Trillions of stars. Our star is located in a spiral galaxy called the Milky Way Galaxy. It resembles the Whirlpool Galaxy in the image below.
Galaxies move through space, many (particularly the Spiral Galaxies) also spin as they move. As the galaxy spins the stars in it orbit a center structure. One current theory is that galaxies have large black holes in their center which all the stars in the galaxy orbit. Our galaxy is 100,000 light years in diameter with a mass of approximately one trillion solar masses.
This image shows a cluster of galaxies, some colliding.
The Life of Stars
Stars form from large clouds of gas (primarily Hydrogen). These clouds are called Nebulas. All atoms have mass, although slight. At some point atoms in the cloud begin to clump together. As the atoms come together their mass begins to create a gravitational force. This gravitational force draws more atoms into enlarging ball of gas, further increasing its mass and gravitational effect. This continues until the ball of gas has drawn all the available gas, or some other process interrupts that addition of Hydrogen atoms to the growing Protostar .
The Horse-head Nebula
These swirling balls of gas are immense. Remember that our star the sun (a small to medium sized star) contains 99.8% of all the mass of our solar system. The gravity created by these protostars force the gas molecules toward the center or core. As the gas molecules are compressed they are forced to collide with each other. The friction of these collisions created heat energy. When the temperature of the core reaches 15 million degrees Kelvin, Nuclear Fusion begins. The incredible pressure and temperature in the core forces the Hydrogen atoms to combine to form a new larger atom of Helium.
It is the process of nuclear fusion (stars are not burning balls of gas) that releases the energy produced by stars. Stars release huge amounts of energy. It is the battle of energy leaving the core and the pressure of gravity pushing in that delineates the final diameter of the star.
A star’s mass and rate of fusion is determined by the amount of gas that is drawn to the forming protostar. This mass and rate of fusion creates stars of different sizes and colors. Scientists categorize stars by these sizes and colors.
The larger the star the faster the rate of fusion occurring in the core. The faster the rate of fusion the more energy released and the hotter the surface of the star. The faster the rate of fusion the shorter the life of the star. This is true even when the star is 20 times as large. The smaller star will have a longer life.
Color Class solar masses solar diameters Temperature
bluest O 20 - 100 12 - 25 40,000
bluish B 4 - 20 4 - 12 18,000
blue-white A 2 - 4 1.5 - 4 10,000
white F 1.05 - 2 1.1 - 1.5 7,000
yellow-white G 0.8 - 1.05 0.85 - 1.1 5,500
orange K 0.5 - 0.8 0.6 - 0.85 4,000
red M .08 - 0.5 0.1 - 0.6 3,000
In the previous chart the size of the star is listed as its solar mass. Since stars are massive scientists use solar mass so they do not have to use the calculated mass in Kilograms or tons. Since we knew the most about our star when scientists started this practice, they used the mass of our star as the base of the system. All stars were then compared to our star, which was given a solar mass of 1. The actual mass of our star is 1.989 x 1030 Kg..
So in the chart on the previous page the yellow- white star with the solar mass of 0.8 - 1.5 solar masses is the category our star falls into. The blue-white star category would contain stars that are 2 to 4 times as massive as our star.
Depending on the amount of fuel (Hydrogen) in the core eventually the star begins to die. As fusion slow downs the star begins to shrink. This is because gravity pushes in on the gas as the outward pressure created by the fusion decreases. As the pressure increases the Helium in the core begins to fuse. This new wave of fusion causes the star to expand. The fusion of Helium releases more energy than that of Hydrogen. This causes the star to swell again, surpassing its original size. As the stars swell the surface area of the star increases. This distributes the energy over a larger area. So even though the star is releasing more energy its surface temperature decreases, making it red.
This is Mira, a Red Giant Star.
Depending on the original size of the star these giant red stars are called a “Red Giant” or a “Super Red Giant”. Of course the Super Red Giant is much larger than a Red Giant. The next stages of the “death process” depend on the size of the stars.
In the case of a Red Giant as the secondary fusion uses up it’s fuel the star shrinks again. This time a large cloud of gas and other stellar remnants floats away in a cloud called a Planetary Nebula (inappropriately named as it has nothing to do with planets or their formation). This is an image of the Cat’s Eye Nebula (a planetary nebula)
After the release of the planetary nebula a Red Giant shrinks again starting to fuse the Carbon in the core (the result of the fusion of Helium). There is less energy being released at this point and the star stays small giving off energy. At this phase it is called a White Dwarf. When the Carbon fusion slows it becomes a Brown Dwarf and then a Black Dwarf.
This is an image of a planetary nebula surrounding a white dwarf.
In the case of larger stars, they expand to even greater size. In this expanded state they are called Super Red Giants. A Super Red Giant does not produce a planetary nebula, rather it shrinks, restarts fusion, re-expands several times. Because it has so much more fuel its fusion rate is fairly high. It repeats this process until it starts to fuse Iron. The process of fusing Iron requires so much energy that it causes the star to collapse and react in the form of a giant explosion called a Super Nova.
Before and after image of a super nova in a nearby galaxy
This Super Nova releases huge amounts of energy and matter. The remaining star matter collapses on itself. This collapsed object has a huge mass, much more than the mass of our star. These objects shrink to an extremely small size (often smaller than our planet). Remember that the original star was much more massive than our star.
One of the objects created in this process is a Neutron Star. It is an object that spins rapidly releasing energy. They were first discovered by picking up surges of energy in pulses, like a light from a lighthouse. For this reason they were originally called Pulsars. Above is an image of a Neutron star amidst the remnants of the supernova.
The other remnant of a Super Nova is a black hole. A black hole is not a “hole”, rather it is a tiny object with the mass of 10 of our suns. It creates such a huge gravitational force that even light cannot escape.
Scientists find the locations of black holes by looking for objects such as stars orbiting what appears to be empty space. They can also find them through large releases of x-rays from an empty area of space. If a black hole is drawing energy from a near by star, the stolen energy heats up as it spirals into the black hole. As it heats it releases x-rays with enough energy to escape.
X- rays
As has been stated already the size of a star determines the rate of fusion that occurs in its core. The faster the rate of fusion, the shorter the life of the star. The size of the star also determines how it “dies”.
Planetary Nebula
Small Stars Red Giant White Dwarf Brown Dwarf�(1 to 3 solar masses)
Large Stars Super Red Giant Super Nova Neutron Star�(4 + solar masses)
Black Hole
The Big Bang
The way it all began?
The Big Bang Theory is the most accepted scientific explanation about the start and formation of the Universe. It is an extremely complex theory that has a lot of portions that are still very theoretical.
The basic premise of the theory is that an infinitely small, dense object called a singularity held all the mass of the universe in an object as small or smaller than an atom. This object expanded rapidly (this is the bang). When it expanded it released all the energy contained in it. This energy changed to matter in the form of Hydrogen. Hydrogen is composed of one piece of positive energy orbited by one piece of negative energy.
Proton- positive
Electron- negative
Hydrogen Atom
This new matter spread away from the location of the singularity. As it moved away the clouds (nebulas) of hydrogen started to form massive stars. These stars created new elements through their fusion and supernovas. These early stars are theorized to have been much larger than any stars currently found in the Universe.
The nebulas began to spread away. More and more stars formed. These stars formed galaxies. This continued to evolve over billions of years until we have our modern universe.
Scientists have searched for evidence of the big bang for many years. Some of the main pieces of evidence are the measurable expansion of the Universe. Using spectroscopes, and the doppler effect, Edwin Hubble was able to show that galaxies are spreading away from each other at a constant rate.
This is a diagram illustrating the doppler effect. This is when electromagnetic energy is compressed as it approaches, or stretched as it moves away. In visible light this causes the spectrum to shift to the blue end of the spectrum as it compresses. It shifts to the red end of the spectrum as it stretches.
The next piece of evidence was when Penzias and Wilson discovered a constant wavelength of background radiation. They were able to show that this radiation was constant and seemed to be evenly distributed. This was a major break through for astronomers seeking to validate the big bang theory. It provided evidence of the “bang”. Here is an image of the microwave telescope they used.
Scientists have recently used more sophisticated microwave telescopes, and high speed computers to generate a map of the background microwave radiation. They are analyzing it for variations in the original spreading of matter.
There is an alternate scientific theory to the start of the universe called the Quasi Steady State Universe. In this theory the universe expands, re -contracts, and re-expands. Almost a series of mini bangs.
Graphic by Moonrunner Design
Big Bang universe
Quasi Steady State universe
Light Year
A light year is the distance light travels in a year. Remember this is a measurement of distance, not time. It is used because distances in space are so great. Light travels at a constant speed of 186,291 miles/second (299,792 Km/second ). This means that light travels 5,878,625,373,184 miles (9,460,730,472,581 Km) in one year. Light energy travels faster than anything else that we know of in the Universe.
The interesting thing about this is that everything we see has traveled to us at the speed of light. That is because for us to see any object, it has to have produced the light we see (stars), or had light bounce off of it (objects). This also means we see objects as they were when the light came from them. This is not very dramatic here on Earth, but has big implications when talking about objects in space.
What this means in terms of astronomy, is the farther we look across the universe, the farther we look back in time. In the diagram on a previous page the star is 4.2 light years away from us. That means we are seeing light that left the star 4.2 years ago. This also means we are seeing the star where it was, and what it looked like 4.2 years ago. When we increase our distances to billions of light years, we are looking at stars or galaxies as they were billions of years ago. As we improve the abilities of our telescopes, we will also improve our ability to look at the formation of the early universe.
�Early galaxies , image taken by the Hubble telescope
On the previous page is an illustration depicting how the Hubble Telescope is able to look back into the history of the Universe. Further improvements in our telescope technology will allow scientists to look even further back into the history of the Universe.
Electromagnetic Radiation
The light we have been talking about, visible light, is one form of energy that is released when atoms are created or destroyed through nuclear fusion, or fission.
Nuclear fusion is when two smaller atoms combine to form a larger atom; such as Hydrogen fusing to Helium in a star’s core.
Nuclear fission is when a large atom breaks apart to form two or more smaller atoms.
Visible light is only one of many forms of energy produced by these types of nuclear reactions. The entire range of energy produced is known as the Electromagnetic Spectrum.
The electromagnetic spectrum contains several forms of energy. Electromagnetic energy has the unique property of moving as both a wave, and a particle. The energy is carried by the particle (called a photon), however the energy moves as a wave. The shorter the wave the more energy the particle carries.
Electromagnetic energy is measured several ways. The measurement we are going to focus on here is wavelength. The distance between two wave crests is considered to be the wavelength. The longer the wavelength, the less energy carried by the photon. The shorter the wavelength the more energy carried by the photon.
Wavelength
The wavelengths in the electromagnetic spectrum are measured in meters. They range from over 100 km (50 miles) to smaller than an atom.
As you can see, only a small portion of the electromagnetic spectrum is perceived by us without special tools. The photons from the visible light portion of the spectrum cause nerves in the back of our eyes to react. These nerves send messages to our brain, and allowing us to see. Each color represents (or is created) by a different wavelength of energy.
Historically we have used visible light to explore space. Galileo used simple visible light telescopes to look into space and observe the planets and stars. A lot of information can be obtained from visible light beyond just the color and shape of an object in space. When we break visible light into a spectrum (separating the wavelengths by bending light) we see the “rainbow” of colors. When we look at light we can often detect portions of the spectrum missing. This is because different chemicals absorb different wavelengths of energy. This gives us information about what the light has passed through on its way to the spectroscope.
Atoms can also produce light if they are excited by energy (as we saw with the Northern Lights). When this type of light is produced it only releases certain wavelengths of energy, not a complete spectrum. This type of spectrum is called and emission spectrum.
Scientists use absorption spectrums to analyze all sorts of things in space. They can look at what chemicals might make up the atmosphere of a planet, or what nebulas are composed of. As light passes through the gas some wavelengths are absorbed. By comparing this to other absorption spectrums they can hypothesize what gas makes up the nebula or planet’s atmosphere.
They can also determine what chemicals are contained in protostars. As the atoms heat up in a protostar, they will give off energy. When scientists analyze that energy they can compare the emission spectrum to known emission spectrums. This allows them to determine what gasses make up the protostar.
A UV-Vis Matrix spectrometer
Scientists use tools called spectroscopes (spectrometers if you don’t look directly through them) to break up the spectrum and analyze the wavelengths of energy. The spectroscopes use prisms (or similar objects) to break up the spectrum and analyze the wavelengths. As we can see from the image on the previous page most of these tools are no longer devices scientists look through. Rather telescopes push light (or digital data) through the spectrometer, which then translates the light information into a spectrum.
Here the spectrum of three different stars are compared.
As we have seen the Electromagnetic Spectrum is made up of many wavelengths and types of energy. Spectrometers can be used to analyze all the different wavelengths of energy. Although we can not see them, those energies are moving through space, and telescopes can magnify them just like they do visible light. Scientists use spectrometers to break up those wavelengths into their spectrums. They then use computer programs to represent them in colors of the visible spectrum. An example would be the map of the microwave radiation spread across the universe that scientists are using to explain the big bang theory. Scientists used a spectrometer to look for certain wavelengths of microwaves, and then translated them to colors to represent concentrations of those waves.
Exploring Space
We have been exploring space since before Galileo. We first used our eyes and mathematics to explore the properties and laws governing the universe. As we developed new technologies we increased our ability to explore the universe. Telescopes were the first invention that extended our view into space. Early telescopes used lenses to increase the amount of light entering the eye. These lenses also adjusted how far our eyes could focus, increasing the distance we could see. This increased the apparent distance we could see.
Telescopes advanced to using mirrors to reflect even more light to the lenses. The more light that reached the astronomers eyes, the brighter and clearer objects were. This also allowed astronomers to focus the lenses further across the universe. We continue to develop larger and larger mirrors. Some are made of multiple pieces that are individually adjusted by computers to give a clear reflection. The largest will be the new Large Binocular Telescope which will use two mirrors that are used to gather light in combination.
One problem is that as light enters our atmosphere is distorted by molecules and temperature variations in the atmosphere. Scientists have tried to overcome this by building most telescopes on high mountains to get above the thickest part of the atmosphere.
Another solution is putting telescopes above the atmosphere. This was done with the Hubble Space Telescope. It orbits the Earth, beyond our atmosphere. This allows it to obtain very clear images with a relatively small mirror. The whole satellite is about the size of a school bus.
We have also expanded our exploration of space by sending probes out to visit distant planets and objects. These probes have greatly increased our knowledge of the planets that share our solar system.
The Voyager spacecraft were two identical probes launched in 1977 that explored all the outer planets, allowing scientists to discover many new things about the planets and their moons. This link gives a good explanation of the mission:�http://voyager.jpl.nasa.gov/window/voyager_ad.htm
Other probes have been used to gather images or samples of other objects in our solar system. Some have been used to map the surface of other planets such as Venus and Mars. Probes have placed robots on Mars. Another probe has collected samples of the solar wind. And recently a probe was landed on a comet to collect samples and return to Earth.
The space probe Hayabusa
Remember that the study of astronomy is very dynamic. New ideas and theories are constantly emerging as more sophisticated data is analyzed. As our technologies improve so will the quality and quantity of information we collect. This will lead to more changes in how we view our universe and the space around us.