| Practical Astronomy |
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Are you a bit of a chemistry and maths numpty like me? This page explains a number of astronomy terms and translates them into terms and visualisations that the layman (numpty) can understand and apply. Most of us don't need to know the mathematics and chemistry behind the cosmos, but it sure helps to understand the mechanics of it all!
I very much hope it helps those who may be entering into the exciting field of astronomy, to give you a knowledge base that is interesting, informative and help you in your journey of becoming waaaaaay smarter than me!
* I must give credit to some of my very educated friends on the Ice In Space Forum, for helping me understand the maths, that I might be able to explain the mechanics.
In the articles I will cover:
Understanding distances - The Astronomical unit. (AU)
Had trouble in the past, visualising just how FAR things are away? Well here's the first step. The astronomical unit (AU). One AU is the distance between the Sun and the Earth, nearly one hundred and fifty million kilometers! Using kilometers as a ruler for these distances can become a little boggling. I mean, who really knows what a million kilometers is? Most continents on Earth are only a few thousand kilometers across!
So, here we have the AU. This is a much easier ruler for measuring distances in our own solar system instead of kilometers. Click on the thumb below for a scale picture to help put this in perspective for you.
Here are some interesting distances in our solar system, using AU as the ruler. (The ± symbol is a plus or minus factor as the orbits of the planets are not circlular, but eliptical.)
Once we are out of the solar system, we start to use light-years (LY) to measure the distances between stars.
Understanding distances - The light-year (LY)
When we start to measure the distances between stars, they become so huge, the AU becomes too small to be useful. Kind of like using your plastic school ruler to measure the distance from one side of Australia to the other.
So we use a bigger ruler. The light-year. Light travels very fast, especially in the vacuum of space. It travels at approximately three hundred thousand kilometers per SECOND! So in a year, it travels nearly ten trillion kilometers!
So, if you are heading home from planet X and engage your warp-drive engine for one more second than you are supposed to, you are going to overshoot Earth by 300,000 kilometers. Hope you have a spare jerry-can....
Radio waves also travel at the speed of light, so here's a comparison. Voyager 1 space probe has been travelling out of the solar system since 1977 (33 years now) at a speed of 17 kilometers per second. That's 61,200 kilometers per hour! As of 25 May 2010, it is 113.573 AU from the Sun. When we send a radio transmission today, it will take 15.63 hours to get there, and 15.63 hours to get back at the speed of light.
Our nearest star (besides the Sun), on the other hand, is 4.2 light years away. That's 270,000 times further away than our Sun is. If someone was standing on this star (Proxima Centauri) and you flashed your torch at it, the person would not see your light for 4.2 years. Similarly, it you were to send a radio signal to them, they would not get it until then and you would have to wait 8.4 years to hear a reply!
 Understanding distances - The Parsec
A parsec is a measurement that is equivalent to 3.26 LY, or a distance of just over 31 trillion kilometers. Earth would have to make one hundred and three thousand trips around to the Sun to cover the distance of a single parsec.
A parsec is calculated using the parallax of 1 arc second. The name has been shortened to parsec. Don't panic, this is relatively simple to explain. To understand this you need to know what the terms arc second and parallax mean.
Arc Second - A circle bisected evenly by 180 lines forms 360 equal sections. Most people are familiar with 360 degrees on a compass, for example. each increment is one degree of arc. (Think of chopping a small section out of a hula-hoop. That is an arc. All 360 arcs added together complete the circle. Each degree of arc is divided into 60 equal sections or arc minutes. Each arc minute is then divided into 60 more sections representing arc seconds. So now you know an arc second is an angular measurement of 1/60th of an arc minute, or 1/3600 of a single degree of arc. There will be a test at the end of the semester...
Kidding...
Parallax - is simply how a fixed object appears to move due to a change in the observer's position. To illustrate this, put your finger out in front of you at arms distance. Note whatever is in the background. Close one eye, then switch eyes. Notice how your finger appears to move from left to right against the background? Imagine your finger is a star, your eyes are the earth in different positions either side of the bridge of your nose (the Sun). The background, is the rest of the visible stars in the universe. Scientists use the same method to measure the distance to stars.
 A star is photographed against background stars from a spot on Earth. Six months later when the Earth is on the other side of the Sun, a second photograph is taken from the same spot. By measuring the distance the object seems to have moved against the background, the arc seconds of parallax can be used to calculate the distance using simple trigonometry. If a star moves 1 parallax arc second, the distance to that star is 1 parsec.
I tried this in my own yard at home. First, I placed out a tape measure, five metres long, at an unknown and unmeasured distance (pretended uncrossable void of space) from my observatory. Then using a stick and a protractor at each end, pointed the stick at the "Star". In this case, the post of the doorway on my observatory. I then took the angle measurements.
 My tape-measure represents the distance from one side of the "Sun" to the other totaling 5 metres (side C), and two angles (a&b). In this case, angle a=71 degrees and angle b=64 degrees. All three angles in any given triangle add up to 180 degrees, so it's easy to work out the angle at the "star" (red X), which must therefore be angle c=45 degrees. Using a trigonometry equation, I can now work out the distances to the "star" (sides A and B) from each side of the "Sun".
Turns out, depending on which side of the Sun we are on, we are between, B = 6.68 and C = 6.35 metres away from the "star" at the red X.
 As you can see by the additional white lines to the green X, this applies in three dimensions. It doesn't have to be on one plane, but can be up, down or anywhere in between.
The problem with using a parsec, is that after a certain distance, (about 400 light years), the angles become too small to accurately define.
Understanding the birth of a star (Typical)
Imagine the most massive cloud of gas and dust floating in a void. All of space contains these particles from very sparse, to very dense regions throughout the universe, particularly within the tight spiral arms of a galaxy. What is not commonly known is that this material exists throughout the unimaginable voids between galaxies!
These elements range from the most common light and basic elements like hydrogen, to the heavier and more exotic elements. They are cast off by stars and other processes much like fumes, smoke and soot billow and spread from a factory chimney.
It is understood that ALL objects, regardless of size/mass, have some level of gravity. Although gravity is one of the weakest forces in the universe, with time is also one of the most influential. Two objects of mass, given enough time, will pull on each other and get closer, unless there is a stronger force to counter it. The denser an object becomes, the more gravitaional force it exerts, attracting other objects nearby to add to it's mass.
Here's a good picture: Temptation(gravity) is weak at a distance, like ice-cream in the freezer. With enough time thinking about it, that ice-cream draws closer and ends up in a bowl in front of you. Unless willpower (the opposing force) is stronger, temptation pulls that ice-cream in, adding to your mass. If you keep it up, you may find yourself attracting more ice-cream......
Within a galaxy the spinning motion combined with tidal gravitational forces, cause these pockets of gas form thick, dense clouds. Other forces can influence how these clouds start to coalesce and become even more dense. In the death of a nearby star, for example, the explosion would cause powerful shockwaves to push these gasses around and compact them into waves, knots and bok globules. You can see some of these bok globules in my photograph of the Eagle Nebula below.
 When one of these globules get dense enough, it starts to heat up. Have you ever used a bicycle pump on a tyre or a football and felt the end of the pump heat up as you compress the air inside? Have you ever seen a shooting star - a meteorite heating up and glowing brightly as it slams into or skips off the atmosphere, compressing a white-hot pocket of air in front of it?
The same principle applies here, except that the MASSIVE amounts of this material compress so much, that the hydrogen atoms inside start to fuse together into a heavier element. This process of FUSION, gives off incredible amounts of energy in the form of heat and light, causing the star to burst into life in a violent release of energy. A star is born. This explosion in turn also creates shock waves, adding to the cycle of other stars beginnings.
Now, without getting too complicated, a star can do different things and take different amounts of time, depending on many factors like the quantity and type of elements present, especially it's mass. In the diagram below you can see examples of the many types and sizes, lifetimes and temperatures.
For our star the Sun, it has reached an equilibrium of stability where it will convert (not burn) hydrogen at a steady rate for quite some time. It is know as a main-sequence star, as it is in the main sequence of it's life, converting hydrogen into helium. The gravity of it's own weight/mass is trying to pull in on itself, while the energy of it's conversion is causing pressure to push it out. At a certain distance from the centre of gravity, both forces reach equilibrium and it stabilises at a certain size/diameter.
As a star gives off energy in the form of solar winds, it blows away all the other elements around it. For the planets that form around it in this mess, this means the solid material like our Earth is made of, is less affected and can stay close, while the lighter materials like left-over hydrogen, are pushed away to form the large gas giants like Jupiter and Saturn.
You can really see this star-wind in action when stars in larger and thicker clouds (called nebulae) hollow out a pocket for themselves like in my photograph below of M78 nebula in the Orion constellation. This is a star-forming region, or a stellar "nursery".
 There are many more examples of these in the Nebulae section of my image gallery. Understanding the death of a star - Supernova
A supernova is a stellar explosion that is so bright that it can briefly outshine it's entire parent galaxy. It can then take weeks or months to fade out. The blast can radiate as much energy as our Sun is expected to emit over its entire life-span. The explosion ejects away all of the star's material in every direction at speeds of up to thirty thousand kilometers per second, or roughly 10% of the speed of light. The shock waves push out an expanding shell of gas and dust called a supernova remnant. One of the famous ones is the crab nebula, which corresponds to a supernova observed by Chinese and Arab astronomers in 1054AD
 The wonderful thing about supernovae, is that they scatter the cosmos around them with heavier elements, the building blocks of solid matter that make the chair you are sitting on and the screen in front of you. Even better still, these mega-powerful shockwaves can push gas and dust around to form more thick clouds, bok globules and consequently, make new stars.
Supernovae can be caused by either turning off or suddenly turning on the fusion process. Either way, it becomes very unstable, like me with too much drink or too little food. Not good for Mr. Star or Mr. Barry.....
So far our observations average one supernova every 50 years in galaxies similar to ours.
Sometimes, when the core of an old and massive star runs out of fuel, it can violently collapse into a neutron star or black hole. More on those down the page...
Understanding the death of a star - Neutron Star
As the core of a massive star gone supernova compresses it collapses into a neutron star. They are composed almost entirely of neutrons, and it is understood that they can't collapse any further because no two neutrons can occupy the same place and state at the same time.
A typical neutron star is roughly between 1.35 to 2.1 times the weight of our Sun and about 24 kilometers across. It is so dense that one teaspoon of its material would be about 900 times heavier than the Great Pyramid of Giza. It is so heavy, its surface gravity is over 1011 times stronger than Earths. To make something this heavy, you could try to squash the entire human population (about 6 billion people) on Earth down to the size of a sugar cube. Messy.....
If you were to fall off your front porch on a neutron star, the gravity is so strong you would hit the ground in one microsecond at around 2000 kilometers per second, or 7.2 million kilometers per hour.. Forget about a shovel or a mop and bucket. All of the different atoms that make you you, would be smashed into identical matter and added to the rest of the star.
To throw a stone into orbit on Earth, you need to throw it up eleven kilometers per second and maintain it. If you tried this on a neutron star, you would have to throw it at 100,000 kilometers per second, or about a third of the speed of light. I hope you have a good arm...
Since the core shrunk in size quickly during the explosion of the original spinning star, it spins extremely fast, then gradually slows down. Ever seen an ice-skater do that spin with their arms and one leg extended? They spin slowly but when they bring their arms and leg in closer to their body, they pick up speed. You can try this on a good rotating stool at home. Get someone to give you a spin while your arms and legs are out, then pull them in and feel the mind-numbing and blistering rush! Go on..you know you want to. Some Neutron stars rotate between once every 1.4 milliseconds to once every 30 seconds.
Currently there are about 2000 known neutron stars in the Milky Way and the Magellanic Clouds (our two orbiting and companion irregular dwarf galaxies). Most of them appear to be spinning and giving off powerful electromagnetic pulses (Pulsars).
Understanding star death - Pulsars As I explained before, many neutron stars spin rapidly. When they do they are called Pulsars. Like our own planet and many others, the axis we rotate on is not neccessarily the same axis our magnetic poles are on. Earth's magnetic pole is off the rotational pole and moves further away each year by about 40 kilometers. Some stars and planets have magnetic poles that are WAY off the rotational axis. The electromagnetic fields send out natural radio signal like beams shooting out of it's axis. As the neutron star spins, those beams can "flash" us, like light from a lighthouse as it rotates. We hear this with our radio recievers like a rapid pulse, hence Pulsar.
Below is a couple of images of the well known Vela pulsar and a sound file of what it sounds like.
Sound of Vela Pulsar
The pulse slows down over time and to date, the slowest observed pulsar has a period of 8 seconds. The gold picture maps on the Pioneer spacecraft as well as on the Voyager probe golden record show the position of the Sun relative to 14 pulsars, which are identified by the unique timing of their electromagnetic pulses. This way our position both in space and time can be calculated by evil aliens. Hello bodysnatching aliens, we are weird looking soft tissued dudes..come and invade, here's my address....we should have given them a wifi to Facebook, they'll run for parsecs...
Black holes First of all, try not to think of a black hole as an opening, like a hole in a piece of paper. Have you ever seen a whirlpool in water? Look at the water around the whirlpool. The water far away is flat and unmoving, yet as it gets closer it starts to swirl around, getting faster and faster. As it gets even closer, the flat surface starts to bend until it eventually gets so steep, it falls over the edge and in it goes. Now try to imagine this happening in every direction simultaneously. Up, down, sideways and every other way, but always pulling into a single spot. This is the essence of a black hole, simply put. Sometimes a star with perhaps over 20 solar masses (twenty times the weight of our Sun) will collapse as it runs out of energy to sustain the pressure that keeps it stable. This could be because it has run out of fuel. It could also happen because somehow it received more matter which does not contribute to its energy production. In either case the energy output is now weaker than gravity's pull so it begins to collapse under its own weight. After various explosions, tantrums and mass ejections of their outer layers, many of these collapsed stars can form different types of compact star, like neutron stars, pulsars etc, depending on the mass of what’s left at the core. So if it is reasonably small, it can’t squash itself any further. E.g. A neutron star. If this dense core is over – let’s say – three to four solar masses, then not even the densest forms of neutrons can stop the crush from continuing. So far, we know of nothing powerful enough to stop the collapse at this point and gravity wins. Gravity goes mad and the core collapses to become a black hole. It crushes several solar masses onto a point so small, it is less than microscopic. IT HAS NO SIZE, BUT INFINITE DENSITY! This is called a singularity. A singularity is so powerful nothing can escape that gets too close. Even light, travelling at 300,000 kilometers per second, cannot come back out once it has gone past the point of no-return, called the event horizon. This is why it is called a black hole, because it cannot be seen directly by conventional means. Black holes do, however, give themselves away by what they do to things around them. Some can be close enough to a companion star, that they start to strip material away from their neighbour. Some of them are close to molecular gasses and other material. As this material is pulled over the event horizon, it gets super accelerated and super heated, giving off all kinds of heat, light, x-ray, gamma ray and other energy signatures. The gravity is so strong it can even distort space-time around it. You might have heard the term, “Time is relative”. From an outside observers point of view, time slows down more and more the closer you get to it, but if you were there, time would feel normal. Looking back out into the distance, everything further away would appear to be speeding! The very fabric of space-time gets stretched and bent. Below is a representation of space-time and distant light being distorted as a black hole cruises by. No matter which direction you view it from, you would see it doing the same thing to everything around it. (The image in the background is a galaxy of billions of stars, seen from the side.)
Numerous black holes have been identified, some locked in stable orbits just as stars are. Others are zooming between the stars like, “rogues”, having been flung out by some cosmic event. One should not think of them as frightening and all-consuming monsters, like the old movies of the 80’s. A black hole has no more “pull” on its surroundings than a star of the same mass. If you fly too close or too slow to a star you will become trapped by its gravity, pulled in and then added to its mass. Same goes for a black hole. In fact, black holes may play an important role in keeping galaxies together, stopping them from flinging off their stars like swinging a bucket of water around your head then letting go. It is thought that super-massive black holes exist at the center of all galaxies, providing the “anchor” that binds them together. After watching the motion of nearby stars for sixteen years, in 2008 astronomers found pretty good evidence that a supermassive black hole of more than four million solar masses is located near the center of our own Milky Way galaxy.
Coming up next -
Apologetics: It is my personal and firm belief that as we use science, hard data and observation to unlock these mechanisms of creation, we are investigating how the eternal and almighty God set-up these interactive and dependent processes and mechanisms to be able to run themselves as He designed them to. While we argue among ourselves about the origins and time frames, none of us yet know the whole story, but that should not stop us from searching and working together.
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