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deefstes,





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

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.

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

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.


Yup, you got me My cover is blown

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.


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 )

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.


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.

Hi deefstes and thanks for the interesting facts about Redshift!

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.

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.

I could read this thread all day, thanks deefstes......Where did the interest in Astronomy start?!

Deefstes?

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.

Cool thread
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

Deeftes!
Thank you for speaking a language even I can understand. You have an audience, don't stop now?

I agree 100% bert...

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

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
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 was taken at Satara camping grounds.

Eish, that is jaw-dropping NightOwl. Well done!

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).

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.

Hi
It's been gtreat 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.
One of my favourite pictures is of the Crab Nebula:

This composite image was assembled from 24 individual exposures taken with the NASA Hubble Space TelescopeÕs 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.

GrahamiNelspruit

First of all, welcome to the Forums. Hope you'll still have lots of enjoyment here.

That is an awesome photo! Surely the best I've yet seen of the Crab! Thanks for posting.