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 Post subject: Astronomy - Give us your trivia
Unread postPosted: Fri Jan 23, 2009 12:44 pm 
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So the intention of this thread is for everyone to share some tidbits of trivia about astronomy. Anything that you know which you think the others may find interesting. Also, ask your questions here, chances are there might be someone who knows.

I'll start with some info of my favourite star, Betelgeuse or Alpha Orionis, the left shoulder of Orion. I've heard various pronunciations of the name Betelgeuse but the most common one, and certainly my favourite, is "beetlejuice".
Image

The reasons I like this star so much is because:

1. It is a fairly bright star. In fact, it is the 9th brightest star in the sky. This is partly because it is reasonably close by (something between 400 and 600 light years) and partly because it is a particularly luminous star.

2. It is a monstrously big star. In fact, we don't know of many other stars that are bigger. It is estimated that it has a diameter 1000 times that of the sun which means that, if it was at the center of our solar system, it would have engulfed Mercury, Venus, Earth and Mars with its surface extending to somewhere between the orbits of Mars and Jupiter. This is on BIG puppy!

3. It is a relatively cold star (in stellar terms of course) and estimated to have only about 20 times the mass of the sun, despite having such an enormous diameter.

This is where things become particularly interesting because, Betelgeuse is nearing the end of its lifetime. In fact, it may have died already but it will take us somewhere between 400 and 600 years to find out about it.

Seeing as Betelgeuse is a red supergiant (relatively cold, very big but not overly heavy) it satisfies just about all the criteria to meet its final fate in a spectacular supernova of note. Its mass of 20 solar masses puts it comfortably over the Chandrasekhar limit which means that it will die in a supernova but not far enough to likely end in a black hole.

When Betelgeuse explodes, it will most likely be significantly brighter than the full moon, making it the brightest object by far in the skies (apart from the sun of course).

Also, the rotational axis of Betelgeuse does not point towards earth so, after the supernova, if it ends up as a neutron star, we will not be bombarded with gamma rays (which could make life on earth rather nasty).

So it seems the makings are there for a truly spectacular stellar event and here's holding thumbs that it happens in my lifetime.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Fri Jan 23, 2009 5:45 pm 
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Thanx, Deefstes!
That is very interesting, more please? :pray:

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Jan 28, 2009 9:42 am 
deefstes wrote:
OK, anybody else? Spill it. We're all ears.


Eish, Deefstes…There is really not much I can contribute to this topic :redface: …..My knowledge about stars only goes as far as that I know they are holes in Heaven’s floor. :lol:
I will however be an avid reader of this topic….especially with such interesting info shared 8)


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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Jan 28, 2009 1:48 pm 
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Aag okay then. Let's see, anyone keen for some introductory astrophysics? Let's have a look at star classification.

With all the gazillions of stars out there it helps to have some sort of a classification system, I suppose this is true for just about any other subject. We have a binomial nomenclature system for living organisms which forms part of a larger taxonomic ranking system. So to better make sense of all the different types of stars there is also a classification system for stars. Here's the rub.

All stars can be sorted according to two attributes:
1. Spectral Type - This is basically the colour of the star and it is a direct function of the temperature of the star.
2. Luminosity - This is basically how bright the star is and is mostly a function of the star's size. Take note that this is not how bright the star appears as seen from earth but rather its absolute brightness.

Unfortunately neither of these two attributes are particularly easy to measure as they are both affected by distance and particularly the latter. The colour of a star is affected by distance because all objects in space are moving away from a certain point (the point where the Big Bang is assumed to have taken place) and very distant objects are moving faster than objects closer by. This means that distant objects' colour is affected by "red shift" more so than objects closer by. I could write up a little something about red shift in another post if anyone is interested. The brightness of a star is affected by distance for obvious reasons.

In order to classify a star it is necessary to know the distance to the star. There are various ways to determine the distance to stars and this is also something that might make for an interesting post if anyone is interested.

Now you may have guessed that hotter stars are also brighter stars while cooler stars are dimmer. This is true for the most part but it is not always the case and there are actually a large number of exceptions. If you where to plot all stars on a graph of which the horizontal axis gives their temperature or colour while the vertical axis represents the luminosity, you get what is called the Hertzsprung–Russell diagram (or HR Diagram for short). Here is a HR Diagram plotted for some 23,000 stars, grabbed from Wikipedia.
Image

Each one of those specks represent a different star and you can clearly see that the vast majority of stars falls in the band called the "main sequence". The HR Diagram holds lots and lots and lots of information and I won't be able to explain all of it here (mostly because I don't understand all of it anyway).

Another very interesting topic is the development and aging of stars. I won't be able to go into that in too much detail either but what I can say at this point is that stars typically begin their life at the bottom right of the main sequence and move towards the upper left as they age. At some stage in the star's life, depending on it's size and composition, it may branch off from the main sequence to become a giant or supergiant. Alternatively, if it does not have enough fuel to burn it can shed its outer layers as a planetary nebula, become a white dwarf and slowly fizzle out, sliding along the white dwarf curve from top left to bottom right (this is in all likelihood how the sun will meet its final demise).

It means the HR Diagram can be used to make predictions as to the future of a star, the age of the star, the relationship to other stars (it becomes an interesting exercise to plot the HR Diagram for all the stars in a specific open cluster galaxy for instance - but that's yet another story).

Just to put our sun in perspective, it can be noted that it falls pretty close to the center of the diagram. It sits on the main sequence at a luminosity of 1 and a colour index of 0.66 (temperature of 5780 Kelvin). This means our sun is a pretty ordinary star. It is still fairly young, has a pretty average temperature and pretty average size.

Betelgeuse on the other hand sits on the very top right of this diagram. It's pretty cold, very big, very old and about to go whallop.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Jan 28, 2009 5:19 pm 
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Hi deefstes, thanks for this great thread. :thumbs_up:

The facts surrounding the HR Diagram are fascinating.

My knowledge regarding Astrophysics is next to nothing but I will sure follow your posts and perhaps get a lot wiser!! :D

So by the way, are you the same deefstes as the deefstes on the SB forums?


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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Tue Feb 03, 2009 4:48 pm 
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deefstes,

Quote:
This means that distant objects' colour is affected by "red shift" more so than objects closer by. I could write up a little something about red shift in another post if anyone is interested.


Quote:
There are various ways to determine the distance to stars and this is also something that might make for an interesting post if anyone is interested.


:naughty: For such an obviously clever, intelligent guy, you say such stupid things!! :big_eyes:

Of course we want to know my magtag, that's why we are here in the first place. So just stop the laziness and type away. :twisted: :twisted:

Thanks for the info so far, it is really interesting.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Feb 04, 2009 10:32 am 
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My word, I've almost forgotten about this thread. But to be honest, I was actually hoping that more people would share some trivia. C'mon guys and gals, I'm sure you've got something to gooi in.

TheunsH wrote:
So by the way, are you the same deefstes as the deefstes on the SB forums?

Yup, you got me :D My cover is blown 8)

OK, so let's look into Redshift a bit. It's a very well known and commonly referenced principle in astrophysics but perhaps not something that the everyday casual skygazer knows.

So, have you ever heard of the Doppler Effect? If so, you understand Redshift already. If not, you certainly have heard the Doppler Effect even if you haven't heard of it.

The Doppler Effect describes the perceived change in pitch (frequency) of a sound when the observer and the source are moving relative to each other. More precisely, when the observer and source are moving towards each other the perceived frequency of the sound is higher while, conversely, when the observer and source are moving away from each other the perceived frequency is lower.

This can be very clearly observed when a police car sounding its siren passes you. As the car approaches you can hear a certain frequency of the siren which then rapidly drops to a lower frequency once the car passes you. The explanation for this is as follows.

Sound waves move at a fixed speed through any given medium (air in the above example). This means that any sound wave emanating from the police siren will move towards you at a fixed speed (more or less 340 meters per second). The frequency of the sound is determined by the wavelength (physical distance between peaks -or throughs- of the waveform). If the sound source is moving towards you, the waveform gets "compressed" so to speak. In other words, while one peak in the waveforem is travelling towards you, the sound source is also moving towards you so that, when the next peak emanates and starts travelling towards you, it is closer to the previous peak than it would have been had the sound source been motionless. This has the effect that the sound wave has a shorter wavelength, resulting in a higher frequency.

Similarly, if the sound source is moving away from you, the waveform is "stretched out" so to speak resulting in a longer wavelenght and lower frequency.

This image illustrates the principle. The sound source is moving from the bottom of the image to the top. Sound waves would have emanated in concentric rings from a motionless source but because this one is moving the waves are compressed towards the top of the image and stretched at the bottom of the image. An observed standing at the top of the image would hear a higher pitched sound that an observer standing at the bottom of the image.
Image

This principle applies exactly to the propagation of light as well. In the sound spectrum long wavelengths equate to low frequencies while short wavelengths equate to high frequencies. In the light spectrum long wavelengths (low frequencies) equate to red colours (outside edge of the rainbow) while short wavelengths (high frequencies) equate to blue colours (inside edge of the rainbow). Because light travels so much faster than sound (almost a million times as fast) the effect is not as readily observed as with say a police siren. Had police cars been moving almost a million times as fast as they do, their colours would have been affected (and no robber would ever have gotten away :D )

In the vast expanses of space things actually do move at those types of speeds and by this very principle their perceived colours are indeed affected. According to the theory of the Big Bang, objects in space are rapidly moving away from a specific point in space, resulting in their perceived colours to be redder than they really are. Conversely, when an objects are moving towards us at such speeds (and thank goodness there are rather few of those) their colours are shifted towards the blue end of the spectrum (blueshift).

An important thing to note is that, to the naked eye, stars appear white. Some stars do seem to have a bit of redder tinge but by and large we can't really tell the colour of a star with the naked eye. The thing is, all stars have varying levels of just about every colour, combined which gives the impression of white (remember, if you mix all colours you get white). But if you were to break down the full spectrum seen of a star into its various colour components, you'd see that some colours are represented more so than others. Here is a spectral breakdown of a type K4III star for instance with the spectral breakdown of pure white light for comparison. You will see that some colours are more prominent than others in the star's spectrum.
Image

When a star like this gets redshifted, the entire spectrum gets shifted towards the red side of the spectrum, meaning that all the bands appear on different wavelengths than they really are.

And that's Redshift. The spectral breakdown of a star tells us a lot about its composition as certain elements that they star may contain will absorb or emit certain wavelengths of light. It is therefor crucial to know by how much the spectrum is redshifted (or blueshifted for that matter) to really know what elements are present, which in turn can tell us about the age, history or relationship to other stars of that particular star.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Feb 04, 2009 11:34 am 
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Hi deefstes and thanks for the interesting facts about Redshift! :thumbs_up:

Herewith my 2 cents contribution to this fascinating thread:

I've saw an article on the net about a star called Eta Carinae. Apparently it has the size about 800 times that of our Sun. Eta Carinae's mass is about 100 times that of our Sun but the most interesting factor is that Eta Carinae is about 4,000,000 times brighter than our Sun!!

Another interesting star is called VY Canis Majoris, it's about 5000 light-years from Earth, up to 2100 times the size of our Sun and about 500,000 times brighter than our Sun.
If our Sun was replaced with VY Canis Majoris, its surface would extend to the orbit of Saturn and light would take more than 8 hours to travel around the star's circumference.


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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Feb 04, 2009 12:40 pm 
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Cool bananas! I didn't know of VY Canis Majoris but just read a little on Wikipedia according to which it is "possibly the largest known star". That is pretty awesome! Imagine a star that fills our solar system to a greater extent than the orbit of Saturn! This is one seriously big puppy.

I've heard of Eta Carinae before. We spent one entire class on it in Astronomy 101 at varsity. There is some uncertainty as it is difficult to accurately measure the luminosities of these extremely bright stars but there is a strong case to be made for Eta Carinae being the most luminous known star as well as the most massive (heaviest).

Eta Carinae is the object of many astronomical studies as it is such a peculiar star. It has a variable brightness and have over the years been observed to range from a star barely visible to the naked eye to the second brightest star in the skies, outshone only by Sirius. It is currently at one of the dim stages of its cycle.

While variable stars are nothing strange to science (there are various different types of stars of which the brightness vary over time) the mechanics of Eta Carinae's variability is poorly understood.

In 1843 the star underwent a spectacular brightening, leading astronomers to think that it exploded in a supernova only to discover that the star was still present after the explosion died out. The fact that the star could survive such a tremendous explosion is an indication of just how immensely big it is. During the explosion it cast off large amounts of mass which is visible today (if you have a VERY good telescope) as an emission nebula. Here's a picture of the star (bright spot in the middle) and the emission nebula produced by the Hubble Space Telescope.
Image

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Fri Feb 13, 2009 3:33 pm 
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OK, here's one that many of you probably already know.

The closest star to us (other than the sun) is actually not one star but two stars revolving around each other. The star is visible to the naked eye as a single star and known as Alpha Centauri. The name Alpha Centauri tells us that it is the brightest star (alpha) in the constellation Centaurus.

Stars revolving around each other like this is known as binary stars or binary star systems. But it gets a little bit more interesting still. Other that these two stars, by the way they are known as Alpha Centauri A and Alpha Centauri B, there is actually a third and much smaller one which may or may not form part of the system.

This third star is known as Proxima Centauri. It is much smaller, much cooler and much fainter than the other two and it is much further from the other two as well. Whether or not this star is gravitationally bound to the other two is unknown but it is known that it is gravitationally affected by the other two. So it is possible that Proxima Centauri orbits Alpha Centauri A&B like a planet orbits the sun or it is possible that Proxima Centauri is slingshotting around Alpha Centauri A&B like a single-apparition comet with a hyperbolic or parabolic trajectory.

The former is more likely but it has yet to be proved. Either way, Proxima Centauri is currently (and will be for thousands of years) closer to us than Alpha Centauri A&B so technically speaking, Proxima Centauri is the closest star to us other than the sun.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Wed Feb 25, 2009 12:36 pm 
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bert wrote:
Cool thread :thumbs_up:
Strange
I am totaly spell bound by the night skies and find it to difficult to learn
about stars etc.
Will follow this thread closely
Might pick up some usefull info for my own education :D


I agree 100% bert... :D

Now just when I read it again and again and again to even try and understand a little bit, the thread has stopped...No more news :(
:shock:

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Thu Mar 26, 2009 8:11 am 
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Deefstes: Thanx for the info on Eta Carinae.
It was actually one of the objects I tried to photograph on the very second night I did AstroPhotography. Now I know a little more about the origin of my picture :dance:
Now I don't have Hubble, but with an Equatorial Mount + 5D Mk II + 300mm f/2.8L Lens, you could get this image...
Image
Image was taken at Satara camping grounds.


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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Mon Mar 30, 2009 10:00 am 
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Eish, that is jaw-dropping NightOwl. Well done! :clap: :clap: :clap:

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Sat Apr 11, 2009 10:20 am 
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The Cosmos:

Cosmology is the study of the overall structure of the universe.
And just what is the Universe?
Quite simply, it is everything that exists.
However, we cannot observe everything in the Universe from earth as some things are dark such as brown dwarf stars, planets, and dark matter and we just cannot see them, additionally there are parts of the universe whose light has not yet reached us in this part of the Universe.
The observable universe is the universe that reveals itself through electromagnetic radiation that can be detected on Earth.
Because the radiation travels at a finite speed we actually look back in time when we look into the cosmos.

Astronomers observe some rather interesting and perplexing structure in the Current Universe.
That structure can tell us much about the History of the Universe.
It can also tell us what we can expect for the Future of the Universe...

A computer simulation depicting a large chunk of our universe
Image is the work of G. L. Bryan, M. L. Norman, UIUC, NCSA, GC3 and sourced from the The Window of the Universe.

When Astronomers probe the deepest regions of space they are actually looking back in time, this is simply because of the finite speed of light.
Light moves at the speed of 300,000,000 meters/second (186,000 Miles/second).
At short distances, like from satellites in orbit of Earth, the light travel time is only a fraction of a second. However, the Sun is so distant from Earth (150,000,000 Kilometers) that its light takes 8 minutes to reach us.
So when you look at the sun in the sky (never look at it directly, you'll go blind) you see it as it was 8 minutes ago.
As distances get larger so does the time frame "look-back time", our closest stellar neighbor, Alpha Centauri (also known as Rigil Kentaurus), is so far away that its light travels for 4.3 years before reaching us.
When we look at the closest spiral galaxy to our own Milky Way, the Andromeda galaxy, we see it as it was 2 million years ago (when Homo Sapiens first began walking the Earth).
Image
Picture of the position of Alpha Centauri and sourced from wikipedia

The theory that best explains the currently observed state of the universe is the Big Bang theory.
This theory states that in the beginning, the universe was all in one place.
All of its matter and energy were squished into an infinitely small point, a singularity.
The laws of physics at that instant are not understood at all.
But something caused the universe to explode, and thus began the expansion that we witness today.
The early universe was small, so everything happened very quickly compared to the timescales on which events happen for the present universe.
At the start, the universe was very small, dense, and very hot.
This stage was called the primordial fireball. For the first second, only elementary particles, such as protons, neutrons and electrons, could exist.
But the universe quickly cooled and expanded.
For about the next 500,000 years electromagnetic radiation was the most important thing in the universe and hence this time was known as the radiation era.
Once the universe had cooled to the point where the simplest atoms (hydrogen) could form, radiation no longer dominated and matter took over, begining the matter era.
The cosmic microwave background radiation was produced at this time, as light that had been trapped by free electrons escaped when the electrons combined with protons to form hydrogen.

So how old is the universe?
In principle, that's an easy question to answer.
With the rate at which the universe is expanding, called the Hubble constant, astronomers can determine how long ago the universe was at size zero - the age of the universe. In practice, it is not so easy.
Despite its name, the Hubble constant is not constant in time.
It changes as gravity takes hold of the universe and slows the expansion.
How much it changes depends on the density of the universe.
To determine this density, astronomers need to measure the distances to very distant galaxies, which is a very difficult task.
Although there is much debate over the current age of the universe among astrophysicists, they do agree that it is somewhere between 10 and 20 billion years old, which is still a pretty good estimate in astronomical terms.

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 Post subject: Re: Astronomy - Give us your trivia
Unread postPosted: Sun Apr 12, 2009 7:43 pm 
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Hi
It's been great reading your posts on things astronomical.
I'm impressed by the photo of E Carina taken in the Satara Campsite.
Only now as the winter approaches is the sky clear enough for star watching.
I was given the thrill of seeing the rings of Saturn through a telescope as well as four of the moons of Jupiter late last year at a gathering of stargazers in the Lowveld Botanical Gardens.

This composite image was assembled from 24 individual exposures taken with the NASA Hubble Space Telescopes Wide Field and Planetary Camera 2 in October 1999, January 2000, and December 2000.
It is one of the largest images taken by Hubble and is the highest resolution image ever made of the entire Crab Nebula.


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