1) the negative paraxes...

...from the topic ''Letter to a friend ''
... the negative parallaxes are a big mistery , as i told many times
... almost nobody want to speak about it , and almost all don't know its existence
... Eistein and de Sitter could not imagine a similar thing
... not only , untill the years 2000 nobody had suspected that existence
... so difficult to understand ! but exactly the half of not near bodies ( stars , galaxies , quasars..) have a negative parallaxes .. and you must make alone all the mental paths around its .. no books , no profs ,no magicians ...: i can only say my opinions ..and discuss with you that opinions , trying togheter a reasonable street where nobody walked .. ( i think that the negative parallaxes ' solution can influence directly the dark matter and the age of universe )
.. main asks and next program : 1) what is a parallax and a negative parallax? 2) how a negative parallax can enter in our science?

wrote:
..from the topic ''Letter to a friend ''
.. the negative parallaxes are a big mistery , as i told many times
.. almost nobody want to speak about it , and almost all don't know
its existence

Assuming you are talking about entries in a parallax catalogue or list, any
astronomer should know why there are negative parallaxes in the list.

.. Eistein and de Sitter could not imagine a similar thing
.. not only , untill the years 2000 nobody had suspected that
existence

Definitely an incorrect statement. Negative parallaxes have been known
about for more than a century.

.. so difficult to understand ! but exactly the half of not near
bodies ( stars , galaxies , quasars..) have a negative parallaxes ..

Your suspicion is correct. If you have a list of parallaxes of very distant
objects, so that their parallaxes are on average much smaller than your
limit of detection, then the errors of parallax are distributed normally,
with a bell-shaped curve plotting the likely distribution of values around a
mean of nearly zero. Hence we expect there to be approximately half of
those published parallaxes with values less than zero and half with values
more.

and you must make alone all the mental paths around its .. no books ,
no profs ,no magicians ...: i can only say my opinions ..and discuss
with you that opinions , trying togheter a reasonable street where
nobody walked .. ( i think that the negative parallaxes ' solution
can influence directly the dark matter and the age of universe )

This sounds a bit mystical. All that is happening is that very distant
objects have parallaxes so small that they cannot be determined with
accuracy, so half are going to be negative and half positive.

.. main asks and next program : 1) what is a parallax and a negative
parallax? 2) how a negative parallax can enter in our science?

If we rejected any measured result with a negative parallax, then we would
decide that the average of the positive values was real, hence we would
deduce that these very distant objects were actually a lot closer than they
really were. This would be a very bad mistake.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

Dne 11/12/2016 v 17:57 Mike Dworetsky napsal(a):


Your suspicion is correct. If you have a list of parallaxes of very
distant objects, so that their parallaxes are on average much smaller
than your limit of detection, then the errors of parallax are
distributed normally, with a bell-shaped curve plotting the likely
distribution of values around a mean of nearly zero. Hence we expect
there to be approximately half of those published parallaxes with values
less than zero and half with values more.

The question remains,
why the data with parallax value within the measurement error
is not replaced by an appropriate note,
instead of publication of noise.

--
Poutnik ( The Pilgrim, Der Wanderer )

A wise man guards words he says,
as they say about him more,
than he says about the subject.

Poutnik wrote:
Dne 11/12/2016 v 17:57 Mike Dworetsky napsal(a):


Your suspicion is correct. If you have a list of parallaxes of very
distant objects, so that their parallaxes are on average much smaller
than your limit of detection, then the errors of parallax are
distributed normally, with a bell-shaped curve plotting the likely
distribution of values around a mean of nearly zero. Hence we expect
there to be approximately half of those published parallaxes with
values less than zero and half with values more.

The question remains,
why the data with parallax value within the measurement error
is not replaced by an appropriate note,
instead of publication of noise.

For exactly the reason I stated in the part of my reply that you snipped:
Negative values are unphysical, but form the part of the statistical
distribution of values that happen to lie below zero when the mean is close
to zero.

Imagine that someone plotted a graph of, say, a spectrum (with low S/N), and
wherever the plotted flux was below zero, they simply truncated it. Would
you be happy with that? I wouldn't.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

Dne 11/12/2016 v 22:50 Mike Dworetsky napsal(a):
Poutnik wrote:

The question remains,
why the data with parallax value within the measurement error
is not replaced by an appropriate note,
instead of publication of noise.

For exactly the reason I stated in the part of my reply that you
snipped: Negative values are unphysical, but form the part of the
statistical distribution of values that happen to lie below zero when
the mean is close to zero.

Positive and negative noise values are equally unphysical.

Imagine that someone plotted a graph of, say, a spectrum (with low S/N),
and wherever the plotted flux was below zero, they simply truncated it.
Would you be happy with that? I wouldn't.

IMHO He should truncated all measurements
with zero belonging to CI of the measurement (mean) value,
as with statistically insignificant difference to zero.

--
Poutnik ( The Pilgrim, Der Wanderer )

A wise man guards words he says,
as they say about him more,
than he says about the subject.

On 12/12/2016 06:42, Poutnik wrote:
Dne 11/12/2016 v 22:50 Mike Dworetsky napsal(a):
Poutnik wrote:

The question remains,
why the data with parallax value within the measurement error
is not replaced by an appropriate note,
instead of publication of noise.

For exactly the reason I stated in the part of my reply that you
snipped: Negative values are unphysical, but form the part of the
statistical distribution of values that happen to lie below zero when
the mean is close to zero.

Positive and negative noise values are equally unphysical.

But you only know for certain that the negative values are unphysical
the positive ones could be real to within some measurement error. Later
more refined experiments may be able to narrow down the error bars.

BTW The speed of light in vacuum with error bars displayed makes
salutary reading for anyone over confident in good experimental method.
Essentially one famous experimenter applied a partial vacuum correction
in the wrong direction for a new method and everyone copied him until an
even more exquisitely sensitive technique gave a different answer. So
for a couple of decades the speed of light was very precisely wrong due
to unrecognised systematic errors. The graph was in an introductory
relativity book but I forget which one - anyone recognise it from this?

Imagine that someone plotted a graph of, say, a spectrum (with low S/N),
and wherever the plotted flux was below zero, they simply truncated it.
Would you be happy with that? I wouldn't.

IMHO He should truncated all measurements
with zero belonging to CI of the measurement (mean) value,
as with statistically insignificant difference to zero.

No. Provided that it is stated somewhere what the limits of detection
for the method actually is then the value determined even if it is
negative is more useful to later researchers than a "below LOD" flag.

--
Regards,
Martin Brown