1) the negative paraxes...

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

Dne 13/12/2016 v 09:44 Martin Brown napsal(a):
On 12/12/2016 06:42, Poutnik wrote:


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.

Later experiment can. But I speak in context of this one.
These small values are not statistically justified,
as there is high probability it is just a noice.



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.

One thing is raw data, other thing is published processed data.
The limits should be available to a team of original data.

Such a limit can be estimated from the fluctuation around zero,
for stars where expected value is low enough.

--
Poutnik ( The Pilgrim, Der Wanderer )

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

Il giorno mercoledì 14 dicembre 2016 08:44:15 UTC+1, Poutnik ha scritto:
Dne 13/12/2016 v 09:44 Martin Brown napsal(a):
On 12/12/2016 06:42, Poutnik wrote:


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.

Later experiment can. But I speak in context of this one.
These small values are not statistically justified,
as there is high probability it is just a noice.



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.

wrote:
Il giorno mercoledì 14 dicembre 2016 08:44:15 UTC+1, Poutnik ha
scritto:
Dne 13/12/2016 v 09:44 Martin Brown napsal(a):
On 12/12/2016 06:42, Poutnik wrote:


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.

Later experiment can. But I speak in context of this one.
These small values are not statistically justified,
as there is high probability it is just a noice.



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.

One thing is raw data, other thing is published processed data.
The limits should be available to a team of original data.

Such a limit can be estimated from the fluctuation around zero,
for stars where expected value is low enough.

--
Poutnik ( The Pilgrim, Der Wanderer )

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

..thanks for contributions to Poutnik , to Mike , to Procarytic ..and
..
.. the old negative parallaxes could keep the errors ..but , i think
, if you repeated its , you could get a very different value nearer
to the rigth-one ...
.. the new parallaxes (HTS) have four significant numbers and if you
repeat , you get the same value ( so the man ,who wrote its , let me
to understand.. ) ( the measures of Bjmag , for galaxies , have the
same five significant numbers also if repeated during years ...) ...
the 'dramaticity' is that : the negative ones are truly negative
because there are intermediate bodies ... (so that man told) ..
.. in 'google astro' you can read the topic 'Link between dark
matter.. ' ...somebody proposes that the dark matter are powders ,
stones , little asteroides.. :so, for having the mass of dark matter
,probabely the sky should be not trasparent and unable to deviate
gravitationally - or rephrationally, then we see that - the ligth for
giving the negative parallaxes ...i suppose the black dwarfes and an
universe ' age many times longer than supposed , so trasparent and
able to deviate the light ...

I don't think any of this is close to reality. Parallax is a geometric
effect due to the earth's orbital motion around the Sun. It would not have
anything to do with refraction or gravitational lensing. If you are
thinking of some sort of photometric estimation of stellar distance, this is
called "photometric parallax" but it has nothing to do with geometry.

.. untill 200-300 y.l. , the white dwrfes are visible almost without
having neg parallaxes ... after it begins the problem.. and the warm
stars ( O,B,A) are deviating the ligth easierly , nearerly ... and
the warm galaxies are desparing easierly , for the same sigth' angle

I'm not sure I understand what you are saying but early type stars have
small parallaxes because they are a long way from us. These are so small
that many measures are effectively zero so individual measures would be half
positive and half negative.

...
.. cutting some steps : in a time almost infinite , the light could
condense like matter in the outern fields and the black dwarfes could
be the fuel and engine of the galaxy..

This does not sound like any physics or astrophysics I know about.
Hand-waving is not the same as carefully reasoned analysis.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)