Distances
http://thunderbolts.info/forum/phpBB3/viewtopic.php?f=3&t=14857
I think most are agreed big bank and red shift are lies, so where does that leave us with distances? When we look at a star with a telescope we can measure very accurately the angle that star subtends, so we can say ,for example if this star is 10 solar radii it must be 200LYrs away ...but we don't know its size, it could be 100 SR then it would be 2kLYrs away , or 1SR and 20 LYrs away. For stars in our galaxy we can measure their movement relative to one another and this will give a picture of the galaxy and where each star is positioned , but there is no measure of distances, no scale.
When looking at other galaxies , again , we can measure the angle they subtend, but is this a small one and 1GLyrs away or a big one ,10 or even 100GLyrs away? How can we know?In order to know the radius of a distant star you would need to know its distance or make an assumption of what kind of star it is first, otherwise one just has an angle and a triangle of unknown dimensions.
The question regarding distances is generally interesting, and it has been discussed here before. See this thread from 2009:
Thunderbolts Forum: "Star distances (triangulation method etc.)"
I did a rough calculation a while back that made me question how we can see stars in the sky with the naked eye when given their supposed stellar distances. The nearest star, Proxima Centaury, is 4,2 LY away. Translating its radius to a white pixel on an average monitor of HD resolution, it would be like viewing that monitor (with its white pixel on a black backgrund) over 600 meters away... Would you be able to spot it? Sure, there are stars of larger magnitude and illuminocity, but they are also much farther away. An interesting thought.Siggy, you used a monitor pixel as a relative scale, but what about intensity? Would you be able to see an electric arc at that distance?
True, the intensity (and received photons per sec by the observer) is the debatable factor. Still, it's a one pixel sized discharge. Perhaps one will get a continous photon feed from the source, and perhaps it will cause a glow within the nearby medium, making it appear larger (but that also alters the factors from which it was calculated from).
Siggy_G wrote:... made me question how we can see stars in the sky with the naked eye when given their supposed stellar distances....
Very nice question ....a search turned up ...."Under today's light polluted skies the most distant star that can be seen with the unaided eye, is the star Deneb, located around 1550 light years away from Earth. However, different estimates from this distance can range between 1400- 3000 light years" Notice how even this 'official' estimate is very uncertain.... lets say 2KLYrs..... 2000 x9.5 x 10*15 = 1.9 x 10*19 meters
surface area of a shell at this radius = 4 Phi R2 = 4.5 x 10 *39 square meters .
area of pupil of eye, one square centimeter = 10*-4 sqm
So the star is emitting 4.5 x 10*43 times more light than the eye intercepts . How many photons need to enter the eye to register the star? who knows ,probably hundreds , but at least one every tenth of a second for a constant image,at 10hz the eye would see a flicker , which it doesn't(lets ignore the twinkling caused by dust in atmosphere) so at the very minimum the star is emitting 4.5 x 10*44 photons , more likely 4.5 x 10 *46 photons , and that's just visible light.
There's a big proviso that the light leaves the star uniformly in all directions, I don't think that's too unreasonable an assumption , if this star was sending out a beam we would expect it to come and go over the hundreds of years of observation, as the star wobbles around, but we don't see this.
So if this star puts out 10*45 photons of visible light how much total power output is this in all forms? and is that possible?.... if it isn't the official distance must be wrong.Metryq wrote:.... I would assume that measuring the angular size of a star becomes useless long before parallax measurement of distance (using Earth's orbit as the baseline)...That is, for any star close enough to measure its angular size, I would guess that we are also able to cross check with a parallax measurement.
Yes you're right , I'd forgotten about parallax, had to search it to remind myself that it's a good technique ........"Under today's light polluted skies the most distant star that can be seen with the unaided eye, is the star Deneb, located around 1550 light years away from Earth.
Deneb is often said to be the farthest star visible to the naked eye, but that is not technically true. Deneb is the farthest of the bright stars, it is a 1st magnitude star and one of the brightest in the summer sky. The naked eye, with ideal seeing conditions, can see stars to about the 6th magnitude. There are probably many stars visible to the naked eye (under good seeing conditions) that are much farther than Deneb.
How far away is the farthest star?The Garnet Star (μ Cephei) discovered by Herschel has a magnitude of +4 and is estimated to be between 4000-9000 light years away. Or even further still is the star V762 Cas in the constellation of Cassiopeia which has a magnitude of 5.8 and is thought to be 16 000 light years away. However, both of these stars are incredibly difficult to see even under perfect conditions.
Although the quote gives the impression that these stars are difficult objects to see with the naked eye, that is not the case if you have good eyesight and are in a dark sky location. Fourth magnitude is pretty easy for the naked eye from a dark sky observing location.
However, these distance estimates must all be taken with a grain of salt and large margins of error.So the European spaceprobes used for measuring distances in the Milky Way using parallax is called Gaia, here is the wikipedia link: http://en.wikipedia.org/wiki/Gaia_(spacecraft)
This thread is very interesting. I was wondering about this the other day, if photons are quantum particles, there must be a certain distance at which they become increasingly sparse. I never thought of it in intergalactic scales, and infinitely small angles etc... Ten photons per second reaching the eye, can we even technically see that without special equipment?Cosmological distances are very complicated, and are based on what is know as the 'cosmological distance ladder'.
Starting at the beginning we have radar measurements of the solar system to give us a value (or values) of the Earth-Sun distance.
With this distance, we can use it to find the trigonometric parallax. Spacecraft such as Hipparcos were instrumental in giving us a good parallax measurement (and also velocity) for individual stars. Gaia will blow everything out of the water once the data is released.
The next step is using clusters, where we can use 'statistical parallax' (Hipparcos was instrumental in refining the models and making this reasonably accurate) to find the average parallax (and therefore distance) to a cluster. Another is using 'Main Sequence Fitting' where the clusters are fitted to the HR diagram with information on their magnitudes and composition. This is really bad as far as errors are concerned, and when we convert to distances, we get large errors.
After this it gets complicated and things branching out to the Cepheid and RRLyrae variables (lots of problems using these 'standard candles'), Novae, Supernovae and so on until we get to the redshift.
I hope you can see the image below (sorry about the quality...
http://prntscr.com/2qb0lz
http://i.imgur.com/0rmLvAK.pngby Nick » Fri Feb 14, 2014 9:44 am
Hi everybody,
I am not an astronomer, but it looks to me like parallax is the only possible method.
Also I have a question about distances:
The distance to Aldebaran, measured using parallax method is 65ly.
The velocity of Aldebaran, according to red shift measurements is 54 km/s.
The Hubble constant is 20 km/s/Mly.
The distance to Aldebaran is therefore 54/20 = 2.7 Millions ly.
Any ideas? Maybe my numbers are wrong?
Please help.Nick, It has real movement relative to us. It's far too close to have any noticable velocity due to expansion and were also told that for some magical reason space doesn't expand inside galaxies.
the so-called "Hubble Constant" (very badly named as it implies Hubble said this) is approximately 500 km/s/Mpc or about 160 km/sec per million-light-years. Not 20. (source = https://www.cfa.harvard.edu/~dfabricant/huchra/hubble/ ) It's irrelevant anyway as the Universe is not expanding - it's another myth of modern cosmological dogma.
neilwilkes, Hubble's original value was wrong. There were flaws in his original work, such as misidentifying stars as variables, not accounting for extinction which wasn't well understood at the time. His original value was flawed it was corrected. Today the accepted value is about 70 km/s/Mpc.
