Star Distance

[AntiThought]

I have been thinking about this problem for quite some time maybe someone else here can help me out.

 

 

Astronomers say that we can know how far a star is from us but I do not understand how. Every measurement has to be taken either by something going to said object (human, tape measure, laser, sonar, etc....) and either returning to relay the distance learned or sending data back remotely..... OR...... by calculating an objects distance to your position based on its distance from 2 objects of known distance and the known distance of you to the other 2 known objects. So how do we know how far a star is? Even if we had a super powerful laser that had the capability of reaching a star and bouncing back to earth there are many things that prevent this from happening in a meaningful way.

 

Such as this, even though a laser moves at the speed of light, to find a star's distance at approx. 300 Lightyears away we would have to not only aim the laser 300 years ahead of its current location on the same trajectory (or 600 years ahead of where we see it in the sky) but we would also have to fire that laser from a point 600 years ahead on Earth's trajectory (allowing for time to travel to and from the star) in order that it even strikes the earth when it bounces back. Even then the numbers will be incorrect as the distance would have vastly increased during the 300 year return trip.

 

So then how can we measure our distance from stars 3,000 lightyears away if it would take even a laser traveling at the speed of light 600 years to estimate a measurement the distance between us and a star merely 300 light years away?

[G!NG3R420]

Also take into account that the "stars" we see could have and most likely are non existant, but is what we actually see is the the returning light of that set star. A star in the sky thats super bright has the ability of being non existant for tens or thousands of years. Adding that factor into the equation, by the time the laser we shoot at that star reaches the vacinity of the origin of what we were normally aiming at, we in turn are shooting at nothing and measuring the distance of nothing in its self, yet we can still see our target.

 

Is it possible that the laser refracts off of the light of the star that is gone and by the time the original laser gets back we know exactly how far that set star was, givin that two objects can only meet half way until they are returning to the original destination where it was emitted from. Half way there, half way back, add both those numbers and that is the givin distance of set target?

[AntiThought]

You have the idea Ginger think about SuperNovas according to Astronomers the star we see exploding actually exploded in some cases 3 million years ago. As for as light bouncing off of light- if it happened (while theoretically possible) would have the effect of dispersing the laser due to millions of photons from both light sources striking at many different angles scattering the light of the laser. What makes a laser so special that we can measure with it is its ability to stay coherent (all photons heading in the same direction) and thus overpower the non-coherent light sources (Sunlight, Moonlight, lightbulbs, etc....). If the laser were to lose its coherency, although some of the light would make it back to the intended point, at distances over a lightyear (in the case of the example tens of lightyears) it would be so dispersed that it would be near impossible if not impossible to detect among the background/environmental photons. Someone correct me if I am wrong.

[PHANTASM]

The traditional method for calculating distances in deep space is to use the redshift of the light. Stars get redder as they get farther away. However, recent discoveries have shown that it is not always accurate (to say the least). So we really don't have a good way of measuring star distances at the moment. Don't tell anyone.

 

I am somewhat of a UFOlogist/amateur astronomer lol.

 

This is from my blog:

 

 

The article below discusses Stephan's Quintet (pictured above), a galactic car accident where several galaxies have slammed into each other. The black holes in their centers destabilized and swallowed millions of solar systems. Many of them were probably inhabited by intelligent life. This is one of the most violent events ever discovered in the universe. This happened billions of years ago, billions of light years away. Or so we have been told.

 

This discovery has a curious side-story: one of the colliding galaxies is calculated to be eight times closer to earth than the others. This is based on its redshift, or how light wavelengths get redder with distance. The galaxy in question is more blue than the others when certain elements are measured that are used to determine its distance. These element spectroscopic lines have been used for almost a century by astronomers to determine the distance of deep space objects. But here we have an object colliding with another object that should be billions of light years apart.

 

This discovery throws much of our knowledge of deep space mapping into doubt. Clearly, our way of determining distance is unreliable. No one will publish this research in a professional journal due to the upheaval this has caused in modern astronomy. Instead they have attacked the author, as usual, but no one can come up with a better explanation. It is quite possible that the "red shift" method of measuring intergalactic distances has exceptions that render it useless in certain situations or with certain types of objects.

 

Very serious stuff.

 

http://cosmiclog.msn...13/1995171.aspx

[+Zippo+]

Me I personally do not know, but I would like too find out. Science is best guess basicly lol.

 

As others have said in this thread, that some stars we see are more then likely gone but the light refracted off them is still reaching us..

 

Just like our sun takes years and years for the light from its core too penetrate the outter parts of the star then begin traveling out into space.

 

 

E: PHANTASM that was very interesting. I seen that picture before or something similar, some were. Just cannot recall were. Think it was on the History channel and something about galaxies

[PHANTASM]

I can explain it better.

 

Light behaves like sound waves.

 

If you've ever had a car drive past you with a loud radio you've noticed the sound changes as it passes you. This is the Doppler Effect. The sound waves get shorter because they are moving towards you and longer as they move away.

 

Light behaves the same way in deep space. Einstein's Theory of Relativity explains that space itself is expanding, so all objects are becoming further apart. When objects are light-years apart the expansion of the universe can actually reach incredible speeds, even the speed of light, at which the objects become invisible to us. This provides a natural limit to how far out in space our telescopes can see.

 

As deep space objects move, the light wavelengths get longer, just like sound waves from a car driving away from you. Light gets redder as the wavelength gets longer.

 

So the light from a known element, say hydrogen, will shift from its normal wavelength to a longer wavelength the further away it is from us. This is how the redshift works. Astronomers use the redshift of light emitted from various elements in a star to measure how much the wavelength has been lengthened, and from that they can calculate how far away it is in light years.

 

Neat huh?

 

The problem is that in objects like Stephen's Quintet the velocity is being disrupted by the presence of other galaxies they are colliding with. So the speed has been changed, and the redshift method gives a false answer. This is a huge controversy right now in astronomy. It's like trying to measure the distance to a car using its Doppler effect of its car stereo - while the car is in a head-on collision.

 

Which means any distant object having its momentum accelerated or decellerated by another deep space object (a binary star, for example) cannot be accurately measured by the redshift method.

[TheDuck]

Wow Phantasm that was really interesting. I had no idea...I thought red shift was a definate fact. I didn't know there would be variables that could eschew the results. Is the galactic neihborhood distances accurate since the distances aren't 'as' far?

[AntiThought]

Thank you for the wonderful intel Phantasm. So glad you found this thred as I expected something was amiss with the calculations. One thing bothers me with redshift though. It seems that to calculate redshift you would have to know the intensity of the various parts of the light spectrum at the source to be able to compare the difference here on earth. Is that true? Not to mention the stars we are trying to calculate distance for that are on the other side of "Dark Matter Clouds" I imagine dark matter really must mess up the redshift's reliability. Any knowledge of these things Phantasm?

 

 

BTW Phantasm we should talk sometime UFOs are an interest of mine as well. Think I am going to go check out your blog.

[G!NG3R420]

Wow Phantasm that was really interesting. I had no idea...I thought red shift was a definate fact. I didn't know there would be variables that could eschew the results.

 

Science is about exploring all the variables. With such a wide mass of un-explorable area, of course space and what is held in captivity there will create many unknowns that we as a human find interesting and have the urge to have an answer for. Many great scientists and astronomers work hard each day creating theories. It is our best answer for not knowing, but based on familiararities and similar occurances we can then in turn find a common ground to explain what has no definate answer. Hence forth the "big bang" and why some beleive of other planets out in existance that hold life similar to our own. Finding solar systems with similarities of ours offers the thought.

 

@Phantasm-I had no clue you were so knowledgable in this aspect. The way you explain the occurances makes it easier to understand what the more intelligent have written. I've heard of the red shift, yet I never really could wrap my head around the studies. Thanks for the intell

[KevinBacon]

This topic screams of Michio Kaku.....

[CaldasGSM]

1st. as said star distance cant be measured by sending something to the star an back.. so we have to measure things by using something that already made the travel.. its light..

 

2nd. redshift a form of Doppler effect, is used to measure the relative speed of 2 objects and with it we can tell if a star is moving away or to us.. but it will be hard to tell the distance.. even if the speed is taken into account in the equation.. is not all of the equation

 

3rd. a method to find the distance of a 2 second point is to have a 3rd point and measure the difference in the angle that those 2 point make.. this is called Triangulation

is a very simple and antique method, but that is still the basis for many modern calculations..

 

4th. If you are thinking how we can get a second point.. just remember that we (on earth) are constantly moving in space

[PHANTASM]

Science is about exploring all the variables. With such a wide mass of un-explorable area, of course space and what is held in captivity there will create many unknowns that we as a human find interesting and have the urge to have an answer for. Many great scientists and astronomers work hard each day creating theories. It is our best answer for not knowing, but based on familiararities and similar occurances we can then in turn find a common ground to explain what has no definate answer. Hence forth the "big bang" and why some beleive of other planets out in existance that hold life similar to our own. Finding solar systems with similarities of ours offers the thought.

 

@Phantasm-I had no clue you were so knowledgable in this aspect. The way you explain the occurances makes it easier to understand what the more intelligent have written. I've heard of the red shift, yet I never really could wrap my head around the studies. Thanks for the intell

 

Thanks.

 

Yeah the redshift is a great tool in general, astronomers have relied on it for almost a century, and without it we would not be aware of other galaxies. Before the redshift, astronomers thought distant galaxies were just one star because they appeared as single points of light. When they realized just how far away they were, they realized they were looking at millions of stars (a galaxy) not just one star in our own galaxy.

 

The redshift measurements have probably always been off by a few percent, and no one cared because the distances were so big. It didn't matter if something was 300 million light years away, or 294 million light years away (a 2% error). There was no reason to suspect anything was wrong. Besides what would you compare it to?

 

Stephen's Quintet showed that the redshift data can be off by a factor of 800%. One of the galaxies in collision measures at 1/8th the distance of the others - it should be nowhere near the collision, but it is. So it is a big issue. The problem is that we have no way to test the redshift itself, because all the measurements were made using the same technique. It's like finding out your calculator is making a rounding error halfway through a math exam.

 

It's possible that the black holes at the center of galaxies can disrupt the redshift by drawing in light. Their gravity can exert a pull that shifts the wavelengths of light used to measure the distance. If so, this is a big problem, because most galaxies have a black hole or two in their center, and also most black holes are invisible to us. So they could be affecting objects that we are not expecting to be influenced by them.

 

I have a lot of this stuff in my blog. I'm also a BIG Mars buff, I am currently examining the latest Mars map (http://jmars.mars.asu.edu/maps/?layer=thm_dayir_100m_v11) for new anomalies.

[MadHatter]

Red shift is definate fact. There is no disputing it's effects. However, as they say, it is not the most reliable method for measuring the distance of a galaxy.

 

You can measure a galaxy's distance away using Hubbles law: v = H*d (V= velocity, H= Hubble's constant and d=distance). Ie You can work out distance as it is proportional by Hubble's constant to a galaxies velocity away from us. You work out the velocity away using the Doppler shift as described above. The wavelength of the radiation emitted, say, from a Hydrogen atom comes in definate quanta. Thus by comparing the new wavelength to the old through this equation:

 

((W-Wo)/Wo)*C = V

 

(W = new wavelength, Wo = wavelength when not moving as measured on earth, C = speed of light, V = velocity). I would type lamda but I don't have that key on my keyboard .

 

 

 

Thus you have the velocity away from us. Note, that Hubble's constant is still disputed today and not truly known. Also, if the galaxy is accelerating or decelerating (possibly due to a collision or so forth) then yes it becomes less accurate.

 

For Cepheid Variable Stars (stars that pulse light), using the stars apparent luminosity, and its absolute luminity, and comparing the two, you can work out the distance away. You do this as from the Period of the pulse, you can work out Absolute Luminosity (M). Apparent Luminosity (m) is simply relative birghtness how it appears and then using d = 10^((5 - M + m)/5) you have the distance in parsecs. This process was discovered by Henrietta Levitt.

 

Also, not that once you have worked out Hubble's constant in the first method by measuring the gradient when plotting Distance versus Velocity, using H = 1/T (T = Age of Universe) you can work out the age of the Universe.

 

Hope this helps. Also, <3 Physics.

 

Source = a course at Cambridge University.

[Connection]

redshift isn't used to measure the distance a star is from us.

 

remember Hubble? showed that the further away from us a star is, the more it's apparent redshift?

well, you would expect that before he could show that, he'd have to have a list of how far away the stars were, wouldn't he...

 

for the most part, astronomers used 'triangulation' -- well a better term is parallax -- to measure the distance to stars. this only works to about 400 light years out though, because of the width of the earth's orbit. parallax measurements basically work like this: you measure the exact location of a star in the sky at some point during the year. 6 months later you measure it again. you assume that the 'background' stars motion is very small compared to the apparent motion of the star you were locating, and do some geometry calculations to get the approximate distance to the star.

 

think of it like this: hold your thumb in front of you with your arm stretched all the way out. close one eye and move your thumb so it covers something far away down the hallway or out the window. now keep your thumb steady and close the other eye ( don't forget to open the other eye! ). your thumb is now some apparent distance from the object it was covering. you know how long your arm is, you know how far apart your eyes are, you can measure how far your thumb appeared to move.. the rest is geometry. draw a picture; it'll make sense.

 

 

but parallax doesn't work very well when stuff is REALLY far away - because you're looking for VERY small apparent changes, even with the diameter of the earth's orbit to work with, space numbers get very big very quickly.

 

when parallax fails, there are a few other tricks. for one thing a star's color spectrum is a good indicator of it's absolute magnitude ( i.e. brightness, but astronomers reserver brightness to describe something slightly different ). . color spectrum is an indicator of exactly what a star is made of ( everything burns a different color ), and we've figured out roughly what a star's life cycle is, which involves burning through different color phases.. so if we know what color a star is, we can tell about how old it is, or at least where it is in it's life cycle. from using parallax and comparing the color of stars with a roughly know distance, a relationship was discovered between absolute magnitude ( how bright a star looks from a given, set distance ) and color spectrum. i.e. stars have a pretty much standard magnitude for any given point in their life cycle. ( look up the "hertzprung-russel diagram" ).

 

long story short, you can see what color a star is. stars with a given color are roughly a given magnitude. now, a 60w light bulb looks so bright when you are next to it, and less bright when you are across the room.. the drop in brightness can be calculated if you make some assumptions about how much 'fog' or dust etc is in between you and the light bulb - or star. so knowing what color a star is, you *know* how bright it would be if you were in the room with it. knowing how bright it seems to be and comparing this with how bright it should bee, you can figure out approximately how far away it is.

 

yeah, there is alot of approximately and guessing involved - no astronomer says such and such is exactly however far - but the distance involved is so big that it's OK to be off a few million miles. 100 zillion 6 million is not much different than 100 zillion 24 million if you get my drift.

 

another trick is to use a 'standard candle' -- there is a type of star called a cephid variable that gives off pulses of light at a regular rate. they're like lighthouses, rotating and shining a beacon at you every time they face you. well the faster they spin, the faster the pulsing.. neat thing is ( thanks, God ) that their luminosity -- absolute magnitude & radiation you can't see; magnitude is only visible light -- can be very precisely calculated if you know how fast they pulsate.

 

basically, if you find a cephid variable in a certain galaxy, you can watch how fast it pulsates and figure out it's absolute magnitude - from it's apparent magnitude you can then figure out about how far away it is. this gives you a rough estimate for the distance to all the stars in that galaxy!

 

there's a type of supernova that's also a 'standard candle' because it's peak luminosity is a known amount.. but you have to be lucky enough to catch one going off to use it to measure anything.

 

there are some other more complicated ways of guessing at it.. if you don't know physics it's probably just going to make your brain hurt even more to read my crappy explanations so i'll stop there. that's the major 3 ways of finding it.

 

thing to keep in mind is that there's alot of estimating and assuming involved, but the distances are so great that the estimates are generally pretty good - nothing too accurate though. the further out, the worse the guess are.. as i said earlier it's only the local 3-400 light years that are really good estimates of distance, because parallax is probably the best bet as there are few assumptions.

 

redshift is NOT a way to determine distance. it's a way to determine speed toward/away from you, but that is a calculation full of assumptions as well. it's only used to estimate the distance of VERY distant galaxies, so far away that we can't use cephid variables or spectral analysis.. you have to assume that hubble's relationship holds for all spacetime at a constant rate, and that the amount of interstellar dust is constant over space and time - both probably bad assumptions - and then you calculate how far away you think it is based on how fast it appears to be moving, using hubble's law.

 

personally i see alot of problems with hubble's law in general.. so working it in reverse to find distance is not a great idea i think. then again, the error involved is still much smaller than the distance involved, so for very distant galaxies it's a good tool. OK i take back what i said about it not ever being used for distance measurements.. i haven't ever done a calculation, but i bet if you try to measure the distance to jupiter, or to alpha centauri using redshift you'd get a poor answer..

 

good question -- ain't it amazing how much you can figure out about something just by looking at it?

[Connection]

@ phantasm -- OOPS i didn't read all the thread before i posted..

 

%800 off LMAO i was not aware of that result. but i have always been skeptical about hubble's law and redshift in general -- i am not at all surprised. as you said, gravitational effects on light cause redshift. interstellar dust causes redshift. for all we know, photons degrade over periods of millions of years, causing redshift. when you think about 70% or more of the matter/energy density of the universe possibly being unknown, you start to wonder just what else might be out there interfering with light and also causing redshift. not surprised at all...

 

thanks for the info!