Larsguy47

OHHHH, that's what happens.

THANK YOU!

This is great because at the very least this is some general astronomy that most people haven't thought about. Though we are considering debates over the text applications of the ancient past, it's still a wonderful science in and of itself. It makes a difference if our walk to class is through a beautiful garden or along the beach versus through a garbage dump.


LG47

RED DAVE

From Larsguy47:
(emphasis added)

From Barbarian:
(emphasis added)

There is a severe contradiction here. Lars is talking some kind of a compression in "midsky," which as far as I know does not take place. Barbarian is talking about something that happens "close to the horizon."

We are obviously dealing with two phenomena, one of which, I believe, does not exist.

From Larsguy47:
I think you counted your chickens a bit before they hatched.

RED DAVE

Barbarian

If "midsky" means close to zenith, well that's the place where there is no atmospheric refraction at all. A deviation of 34' is observed not just close to but at the horizon, but it falls sharply as we deviate from a horizontal line of sight, dropping to 5' at 10 grades. This deviation only impacts the altitude, not the direction, so two stars at the same altitude will not show any variation in their relative positions.
I am sure you are not referring to atmospheric refraction here. Atmospheric refraction will raise the apparent positions of bodies with a low altitude, so it will in essence apply a small vertical compression to constellations very close to the horizon. The optical illusion of the Moon appearing to be bigger when closer to the horizon is as of yet unexplained, but cannot be caused by atmospheric refraction because such refraction would - and does - turn the Moon into an ellipse, with short axes being vertical. In fact, the Moon illusion does not impact instruments, only our eyes, so it must be purely psychological.

Barbarian

I did not notice earlier that Larsguy47 talks about stars appearing closer to each other towards the zenith, probably because when I first saw the claim, I immediately thought "atmospheric refraction" and misunderstood the rest. Sorry about that. Larsguy47: there is no way to link atmospheric refraction to your claimed visual effect, in fact, they work in directly opposite directions.

Larsguy47

YES! I see now. The "compression" appears near the horizon and the "expansion" in midsky for the zodiac stars. So indeed, this was mistated by me. I had in mind the opposite. So my correction is that they do "compress" toward the horizon but expand in midsky.

Having corrected that, my point remains that the Babylonians thus decided to set a STANDARD distance between certain major stars that they always used for measurements. That is, for instance, the distance between say beta-Virginis and Sigma-Leonis would always be considered to be divisible by 3 cubits, regardless of how that distance is increased or lessened depending upon the position of the constellation in the sky. Thus it is a "relative set distance" between the various stars. This added consistency of measurements.

Thanks for handholding me though this, RED DAVE...:redface: It's been a while since I became acquainted with this.

At any rate, the stated distance between beta-Virginis and sigma-Leonis in terms of "fingers" for some reason was stated as 30, which averages 10 "fingers" per cubit. But this apparently is not always consistent and may not be a standard asignment for every star distance. I've seen different values for "fingers" noted in some literature.

Thanks Dave!

:wave:

Larsguy47

Exactly! I stand corrected. It's just the opposite. I had in my mind that the size of the zodiac constellations did vary in midsky from when close to the horizon in real life. But for astronomy programs I think it's the opposite which causes the wrong impression. Or maybe I just got it wrong. I think when you try to make something spherical expand flat then it expands at the edges (i.e. like Greenland is this huge island in many maps? when longitude and lattitude are equidistant over the whole map?).

Anyway, I appreciate standing corrected here, thanks to RED DAVE trying to figure out what I was saying while stumbling over myself.

MY MAIN POINT, however, was that was the basis for assigning specific distances between the star positions by the ancient astronomers because that precise distance did vary as the contellation moved acoss the sky during the night. If a standard "relative" distance of measurement was established then the references were consistent throughout. The main interest was in uniformity and not necessarily the actual distance between the stars.

But thank you for explaining the scientific phenomenon.

Plus I guess it's different for the Moon, which appears larger near the horizon, does it not, than in midsky?

Anyway, now that we are all "on the same page" here, I guess RED DAVE is happy, finally.

LG47

Barbarian

Not only the Moon but all celestial objects appear larger when close to the horizon - the Sun visibly so. However, this is a purely psychological effect, objective measurements cannot replicate it. If you hold a properly sized ring at an arm's distance such that the Moon appears to fit well with the ring, you would see that the big Moon near the horizon fits the same ring as the little Moon close to zenith. Nothing happens to the light which would make its source appear bigger near the horizon - only its mental image is constructed that way, and we don't know for sure why does this happen.

Larsguy47

Wow. Very interesting. But obviously since lunar and solar position in relation to the stars, which appear to be closer together at the horizon, compared to the larger sun and moon, there would be some need for standardization since the same observation at midsky would seem to be slightly different. I'm imagining they had some type of a ruler or T-square which they could move back and forth so that the standard distances were maintained between two stars, etc.

LG47

Barbarian

Unfortunately, the atmospheric refraction is not fully predictable near the horizon, so astronomers typically don't even look at objects with low altitudes. When they do, they apply corrections, but IIRC I have read that the first astronomer to do so was Tycho Brahe. For the Babylonians to actually apply corrections, they should have realized that the aberration is an apparent one due to refraction of light instead of being a real change of motion, but it is unlikely that they were able to make that deduction.

Larsguy47

Thanks for the information. But again, I don't think they were concerned about measurements or changes in the measurements, only standardizing the relative distances. This addresses the very fundamental optional illusion of some stars being closer together near the horizon than in midsky, but if you have a standard distance between those stars, then that standard distance would vary and adapt to the subjective optical perception.

QUESTION FOR YOU: Since you are monitoring this, there is an issue involving the VAT4956 that relates to potentially why Sachs/Hunger incorrectly inserted "the moon" in Line 18 where they should have inserted Venus. That's because in older texts the "Rear Foot of the Lion" (GIR ar sa UR-A) was always a reference to the actual foot of Leo, sigma-Leonis. That is the star assignment apparent in the VAT4956. But in later texts from the Seleucid Period, the Rear Foot of the Lion was assigned to beta-Virginis. So in Line 3 of the VAT4956 Sachs/Hunger notes the position of the moon in relation to the RFL as a reference to beta-Virginis. But since Line 18 associates the "Bright Star Behind the Lion's Foot" (MUL KUR sa TIL GIR UR-A) with the star behind the Lion's foot, it follows the old application and thus Sachs/Hunger misrepresent the text. Thus if no one noticed this, the issue of the fact that the latter texts change the name of this star never comes up.

But having noted this to be the case upon correcting the star assignments in this text, since the lunar distance between beta-Virginis and sigma-Leonis is 3 cubits and thus 12 hours, it is suggested that the later Seleucid astronomers purposely changed the lunar times by around 12 hours or so and renaming this star facilitated this change.

MY QUESTION is, however, generic and not related to any "conspiracy" theory regarding this. But, with the renaming of this star, where the moon appears in a position now that it would not oridinarily have reached until 12 hours later, would this be read (if not understood as a fabrication) as the Earth's rotational speed slowing down or speeding up?

I'm thinking if the moon in relation to a given time, say midnight is 12 hours father down range it suggests the moon is moving faster than we thought and thus the Earth's rotational speed must be slower. That is, the Earth is moving so slow that the moon was able to get to a place much 12 hours lunar time beyond what we might calculate for the current speed of the Earth.

OR am I confused here? Does this really mean the Earth's rotational speed has sped up?

In other words, given an ancient astronomical text that notes the position of the moon say 1 cubit in front of the "Rear Foot of the Lion" right at sunset, and the RFL was a reference to sigma-Leonis, but once the RFL is now changed to beta-Virginis, would be presume the Earth's rotation had sped up? Or slowed down?

If what I'm thinking is correct, that the advancement of the moon suggests the retardation of the earth, then the changes made during the Seleucid Period of adding 12 hours to lunar times for whatever reason, actually slowed the earth down compared to it's current speed. That is, the earth was moving SLOWER back then than it is now. That is not consistent with the concept that the Earth was moving faster and is now slowing down. But it is clear that it makes more sense that the Earth might be slowing down gradually (even though it's not right now, the earth's rotational speed doesn't vary within a millisecond) than speeding up gradually. But this can be easily reversed if you either added or subtracted 1 day (I don't know which) to the timeline. That is, if you adjust the lunar position by 12 hours, it will appear 12 hours earlier than normal for one day but 12 hours later for the previous day if a date were added or removed.

At any rate, besides the apparent name change for beta-Virginis in later texts (but not the VAT4956) you have line 8 in the text to deal with. It records, amazingly, the position of the moon at the time of sunset! OOPS! The moon is 4 cubits below beta-Geminorum "while the sun stood there", thus when the moon becomes visible just before sunset. That coordinates for the TEXT the precise coordination between solar time and lunar time and position. Problem is, when you look at sunset from Babylon on this day, the moon is advanced some 10.5 to 12.5 hours as close as I can calculate. It is slightly 1 cubit below beta-Geminorum, meaning 3 cubits' difference, or about 12 hours, close to the same timing between sigma-Leonis and beta-Virginis.

But again, that also suggests the revisions made in later texts, upon which the astronomical programs are based, were though rather opportunistic, still results in the impression that the Earth's rotational speed was slower rather than faster. At least that's what I'm thinking. But I'm thinking I don't understand this fully and it might mean that the revision suggests the Earth's rotational speed actually is faster. GRIN?

If you want to pass on this, that's fine. But it's part of the issue with correction of the references in the VAT4956, because of line 8 and also the renaming of beta-Virginis as the Rear Foot of the Lion, which Sachs/Hunger inapparopriate applied for this particular text, though not for many others. I think they were kind of hard pressed to expose the change and decided it better to distract from the problem by inserting "the moon" in that position rather than Venus. Inserting Venus there would expose the problem, of course, but leaving it blank would be the same as inserting Venus there because everybody noticing the description of a planet on the 15th of the Sivan immediately below the "bright star behind the Lion's Foot" would see that Venus was below beta-Virginis on this date. So leaving it blank would be the same as putting Venus there, since it would invite an empiric fill-in. By putting the "moon" in that blank and not noting "error for the 5th" or something as they did in Line 3, it's less noticeable. If there is no problem noted here, as they had before, you presume all is well. And who would notice this unless they were recharting the entire text or checking behind Sachs/Hunger on this?

Thanks!

LG47