Distance Calculations

[Aardwolf]

Of course, the fact that they threw out all the negative and zero parallax measurement data I'm sure is irrelevant. The data that supported what they expected to find is the important stuff anyway...

my highlights.

You all, make these blanket statements. Here is some big picture perspective;

Some 20,000 distances were determined to better than 10%, and 50,000 to better than 20%.

Hipparcos Catalogue:
Number of entries 118,218

http://en.wikipedia.org/wiki/Hipparcos

So what portion of this is discarded valuable data? If its in the remaining 48000, it won't discourage me much.

Surely a true scientist would investigate why some of his data is unexpectedly null or negative. If there is some phenomena causing some data to be null or negative then surely there is potential for that phenomena to affect the positive parallax measurements as well.

But of course when you spend a billion dollars you dont really want data that disproves your measurment theory.

[fosborn_]

Of course, the fact that they threw out all the negative and zero parallax measurement data I'm sure is irrelevant. The data that supported what they expected to find is the important stuff anyway...

my highlights.

You all, make these blanket statements. Here is some big picture perspective;

Some 20,000 distances were determined to better than 10%, and 50,000 to better than 20%.

Hipparcos Catalogue:
Number of entries 118,218

http://en.wikipedia.org/wiki/Hipparcos

So what portion of this is discarded valuable data? If its in the remaining 48000, it won't discourage me much.

Surely a true scientist would investigate why some of his data is unexpectedly null or negative. If there is some phenomena causing some data to be null or negative then surely there is potential for that phenomena to affect the positive parallax measurements as well.

But of course when you spend a billion dollars you dont really want data that disproves your measurment theory.

So how much is bogus and how much is good? Your short answer is you don't have clue?

[Aardwolf]

Of course, the fact that they threw out all the negative and zero parallax measurement data I'm sure is irrelevant. The data that supported what they expected to find is the important stuff anyway...

my highlights.

You all, make these blanket statements. Here is some big picture perspective;

Some 20,000 distances were determined to better than 10%, and 50,000 to better than 20%.

Hipparcos Catalogue:
Number of entries 118,218

http://en.wikipedia.org/wiki/Hipparcos

So what portion of this is discarded valuable data? If its in the remaining 48000, it won't discourage me much.

Surely a true scientist would investigate why some of his data is unexpectedly null or negative. If there is some phenomena causing some data to be null or negative then surely there is potential for that phenomena to affect the positive parallax measurements as well.

But of course when you spend a billion dollars you dont really want data that disproves your measurment theory.

So how much is bogus and how much is good? Your short answer is you don't have clue?

Still irrelevant. If they dont know the cause of the problem they have no way of knowing if it effects 1% or 100% of the "good" data. Laughing at the results won't help either (although I'm sure they have a few giggles at the expense of tax-payers).

[fosborn_]

Your proving nothing. Can you produce any information to back up what your saying?

[Aardwolf]

Your proving nothing. Can you produce any information to back up what your saying?

Why? Is there something wrong with your search engine? Why not have some educational fun and research it yourself.

[fosborn_]

Your proving nothing. Can you produce any information to back up what your saying?

Why? Is there something wrong with your search engine? Why not have some educational fun and research it yourself.

"The onus is on you"

Not on PC on blackberry. Hard to search with my thumbs.

[Aardwolf]

Your proving nothing. Can you produce any information to back up what your saying?

Why? Is there something wrong with your search engine? Why not have some educational fun and research it yourself.

"The onus is on you"

Not on PC on blackberry. Hard to search with my thumbs.

No rush. Research later.

[nick c]

With regard to negative parallax, it is my understanding that given the assumptions of the measuring method there are situations where one should expect a negative result. That is to say, the method requires that some stars will turn up with a negative parallax. If a star is so far away that its' true parallax is less than the margin of error, then measurements made 6 months apart may yield a negative, ie the star's apparent movement is the opposite of the expected direction. Negative parallax does not - in itself - indicate a flaw in the method, but is the result of the lack of precision with respect to that particular star.

[Aardwolf]

With regard to negative parallax, it is my understanding that given the assumptions of the measuring method there are situations where one should expect a negative result. That is to say, the method requires that some stars will turn up with a negative parallax. If a star is so far away that its' true parallax is less than the margin of error, then measurements made 6 months apart may yield a negative, ie the star's apparent movement is the opposite of the expected direction. Negative parallax does not - in itself - indicate a flaw in the method, but is the result of the lack of precision with respect to that particular star.

Some of the negative parallaxes are way in excess of the error margins. Some very small negative values may be acceptable but it makes absolutely no sense to have large negative parallax measurements. Nothing can explain these results except an error in the theory. A large negative parallax means the star moved in the wrong direction compared to background. Either there is something wrong with the theory or the background used to determine the parallax for these stars is actually the foreground.

[Aardwolf]

For example, objects 3253-693-1, 2853-306-1 & 4828-1651-1 have parallaxes of -799.8, -904.4 & -919.1 respectively, which means if they actually moved in the correct direction compared to their backgrounds, would all be closer than Alpha Centauri at 742.1

[nick c]

A negative parallax that is beyond the margin of error could possibly be explained simply as a mistake in the measurement. This could be verified by remeasuring. Again out of the many thousands of measurements made, some anomalies must be expected. This in itself is no reason to discard the method.
Well then, if the negative parallax is determined to be real and far greater than could be attributed to margin of error, what could be the cause?
One possibility that comes to mind is large proper motion of the star. This would indicate that the object is nearby and the proper motion is offsetting or canceling out the parallax. Nearby stars can exhibit large proper motions compared to their measured parallax.
For instance, Barnard's Star has a proper motion of more than 10 arc seconds per year! parallax of even the closest stars is measured in thousandths of a second of arc. So it is not inconceivable that in some cases a nearby star could be cancelling out the parallax with proper motion.
It seems to me that the method (trigonometric parallax) is sound if not perfect, and it gives reasonably accurate measurement of stellar distances (in our galactic neighborhood) with the margin of error increasing with distance.

[Aardwolf]

A negative parallax that is beyond the margin of error could possibly be explained simply as a mistake in the measurement. This could be verified by remeasuring. Again out of the many thousands of measurements made, some anomalies must be expected. This in itself is no reason to discard the method.
Well then, if the negative parallax is determined to be real and far greater than could be attributed to margin of error, what could be the cause?
One possibility that comes to mind is large proper motion of the star. This would indicate that the object is nearby and the proper motion is offsetting or canceling out the parallax. Nearby stars can exhibit large proper motions compared to their measured parallax.
For instance, Barnard's Star has a proper motion of more than 10 arc seconds per year! parallax of even the closest stars is measured in thousandths of a second of arc. So it is not inconceivable that in some cases a nearby star could be cancelling out the parallax with proper motion.
It seems to me that the method (trigonometric parallax) is sound if not perfect, and it gives reasonably accurate measurement of stellar distances (in our galactic neighborhood) with the margin of error increasing with distance.

Errors in measument and motion is taken into consideration. These are genuine negative parallax measurements and there more than just a few anomalies. They are counted in the thousands.

If these can't be expliained (which they haven't) it brings in to question the whole theory. How can you trust any of the positive readings if you dont know what's causing the negative ones. There are thousands of stars that have no distance measurement so they are ignored. It's not a case of the further away, the less certainty. If something has a parallax of 200 milliarcseconds it should be relatively nearby. It can't be distant because it would be moving too fast. The problem is when it's negative and moving in the wrong direction. If, as you suggest, that these anomalies are caused by their proper motion, then how do you determine that all the positive parallax stars are not subject to exactly the same motion problem. It brings in to question every single measurement if the motion determination is suspect.

Science has decided that becasue they are positive we trust them but all the negative ones we can ignore because they dont fit. That's not science.

[Aardwolf]

Consider that object 4828-1651-1 has a negative parallax of nearly 1 arcsecond. If they can't determine the proper motion of this star from a negative parallax of 1 arcsecond then they have a serious problem.

[fosborn_]

For example, objects 3253-693-1, 2853-306-1 & 4828-1651-1 have parallaxes of -799.8, -904.4 & -919.1 respectively, which means if they actually moved in the correct direction compared to their backgrounds, would all be closer than Alpha Centauri at 742.1

I queried SIMBAD and got zero results on finding these objects.
And sense this is a science thread not NIMI, its good form to post your sources.

[Aardwolf]

For example, objects 3253-693-1, 2853-306-1 & 4828-1651-1 have parallaxes of -799.8, -904.4 & -919.1 respectively, which means if they actually moved in the correct direction compared to their backgrounds, would all be closer than Alpha Centauri at 742.1

I queried SIMBAD and got zero results on finding these objects.
And sense this is a science thread not NIMI, its good form to post your sources.

You need to try harder. They're easy to find. Have fun.