Clarification wanted regarding the claim that only positive parallax is possible in the heliocentric model

Dear Simon and others!

In the tychos book it is written:

“In order to SEE any stars, you will have to look out of your righthand window - at all times. Therefore, if you were to measure any stellar parallax (of relatively nearby stars - against more distant ones), only “positive” parallax could possibly be observed - at all times. In other words, the nearby stars will ALWAYS seem to move from left to right (or from east to west) in relation to the more distant background stars. Here’s a conceptual graphic illustrating this indisputable fact:”

This picture is quite understandable, but some nights ago I had a disqussion with a friend (a very convinced heliocentrist), which led me to draw this picture:

So if the premiss is, that you only measure the parallaxes with intervals of a half year (and we only look at the stars located somewhere near the eccliptik plane),then it seems, that it is, at least in theory, possible to see as much negative parallax as positive, since the ”western” stars will show a negative parallax if you start the measurement in ”spring” (seen from the viewpoints B1 and B2, and the ”eastern” will show positive (seen from the viewpoints A1 and A2) .
And if i am allowed to use Simons terminology cited above, it seems to me that, in order to see the eastern stars you must use ”the front window” (Viewpoint A1 in my picture) and thus you can use ”the back window” to see the western stars (Viewpoint B1). Consequently, if you use ”the righthand window (in ”spring”) you can see the southern stars, but you will never be able to see the southern stars at ”fall”, beacause then your vision will be blocked by the sun light and perhaps even the sun itself, (and thus zero parallax should be impossible).

(It aslo follows from my picture that the same stars will show either positive or negative parallax depending on wether you start the measurement in ”spring” or ”fall”.
Another thing that follows from my picture is that it should be impossible to find any zero parallax, since the sun (light) is blocking the ”southern stars” in ”fall” and the ”Northern stars” in ”spring”, which doesnt seem to fit at all with 50% zero parallaxes that is actually observed.)

So since atronomers seem to generally regard negative star parallax as a problem for the heliocentric model, then…well lets say that either I have missed something or there is something missing in the description of the (astronomists jargong?) term ”negative star parallax”.

So please help me out, what is missing here?!

With kind regards, Gunnar!

For me it is much easier just to stick with the direction of the drift,

Whether or not you begin your measurement in spring or fall would not make any difference since we are always moving counter-clockwise around the sun.

When they use the term “negative” they’re saying the star has gone the opposite direction! Unless we’re backing up, that cannot happen.

1 Like

Dear Gunnar,

Yes, you are absolutely right about ONE thing, my friend: it is you who are missing something ! :wink:

I’m sorry but at this point I don’t know how I could further clarify this matter for you - other than reiterating everything that is explained and illustrated in my book and in this forum. And no, your heliocentric drawing does not show that, as you wrote, “it is, at least in theory, possible to see as much negative parallax as positive,”

All I can say is that you evidently need more time to wrap your head around the concept of stellar parallax - but don’t feel bad about it: it took me a couple of years to fully grasp the issue and the astronomy jargon that goes with it… To be sure, one of the few points in which the TYCHOS is in agreement with the heliocentric model (and its proponents) is that negative parallax would be physically impossible under the latter. Your convinced heliocentrist friend should know better, namely that ALL Copernican astronomers - without exception - agree about this pesky issue which have kept tormenting them for centuries and even up to this day. The below extract from a recent ESA report ( the"GAIA DATA RELEASE 2" ) bears testimony to this fact:

Since inverting negative parallaxes leads to physically meaningless negative distances we are tempted to just get rid of these values and form a “clean” sample. This results in a biased sample, however.

Perhaps the most ironic “twist” of the entire history of stellar parallax detection - and as very few will know - is the fact that Bessel (the man credited for making the first "indisputable stellar parallax determination that finally proved Earth’s motion around the Sun "), INITIALLY detected and reported a number of negative star parallaxes - as revealed in a treatise by M.E.W. Williams in 1981 titled “Attempts to measure stellar parallax - from Hooke to Bessel” :

" But Bessel was to be disappointed again: when he had finished the reduction of the position of 61 Cygni relative to the six different stars he was forced to the conclusion that its parallax was negative! The paper in which this result was announced took the form of a report only, with no explanation of why a negative answer might have been obtained. "

But yes, Gunnar, you are correct with regards to stars exhibiting ZERO parallax (which make up almost 50% of all stars listed in the official stellar parallax tables!). These would also be absurd - or at least highly unlikely - under the tenets of the heliocentric model - whereas they would be fully expected under the TYCHOS model.

1 Like

Dear Gunnar, I now see what the confusion is all about…

See, firstly I don’t think astronomers would often choose to measure the parallax of stars which will be located for most of the 6-month period in the daylit portion of the sky. But here’s the thing: even if they did so (say, one observation of a ‘western star’ at B1 and another six months later at B2), they would consider this - under their heliocentric perspective - to be a POSITIVE parallax result, not a negative one ! This because, ‘in their world’, they would fully expect that the Earth would move “from left to right” with respect to a “western star” (as of your above drawing).

Phew - I hope this clarifies the matter! :slight_smile:

In order to further clarify, here’s how the proper meaning and generally-accepted implication of “negative stellar parallax” should be ideally defined - in the (heliocentric) dictionary:

Negative stellar parallax: A given parallax measurement of a star that yields a result which contradicts the expected motion of the Earth around the Sun and our orbital displacement in relation to the measured star vis-à-vis the ‘fixed’ background stars.

1 Like

Dear Simon!
I agree with you that it seems unlikely that astronomers would (ever) choose to measure stars that will be daylit for the most of the half year.
And I also agree about the definition of (the astronomists jargong term) “negative stellar parallax”, (even though I want to make the remark that, with this definition, if we are going to be exact, also zero stellar parallax will be found negative, which is also somewhat confusing, since zero parallax is also impoosible in the heliocentric model.)

No, there is not a problem here with regard to sucject in itself, but there is a retoric problem (that is how we best shall describe the subject).
So your words:

are perfectly true if we add the quiet assumption "As long as we are looking at the “eastern” stars (I mean “eastern” from my drawing).
And, as we both agree upon, problably there have been very few, if not any at all, parallax measurements, looking at the “western” stars. So it would be easy to solve this retoric problem just by adding this information (that “parallax measurements” mean (almost) always looking at the “eastern” stars) , perhaps in a note.
Phew - yes the matter is now clarified!

1 Like