PDA

View Full Version : Are rapid changes in earth's orbital period possible?

Ara Pacis
2006-Jun-22, 05:33 AM
I ran across this page (http://www.direct.ca/trinity/360vs365.html) while looking up something about calenders and thought I would see what you guys thought. (I'm not promoting the idea he describes.)

The page calculates that if the earth orbited the sun fast enough that there were 360 24hr days in a year that the moon would also rotate faster so that a month would be 30 days making everything fit into 12 even months. He then claims that this was the type of reckoning used in the Bible and other ancient calender systems and uses that as evidence that the earth really had a 360 day year.

The difference in speed between 365.2422 days per year and 360 days per year is equal to 20.9688 minutes per day. This is not a difference in our 24-hour time period but it would take the earth 20.9688 minutes less time per day to travel that same distance in the orbit around the sun.

365.2422 days -20.9688 minutes per day = 360 days

If you had a year = 360 days per year and slowed the orbit of the earth around the sun by 0.433792 km/s (The difference between 30.22379 km/s and 29.79 km/s), you would end up with a year that takes 365.2422 days. This slower speed would cause 5.2422 days extra per year to make one complete revolution around the sun

There is no time dilation or anything extraordinary here. We have only slowed the speed of the earth down. We have not changed spin of the earth in a 24-hour period and we have not changed the speed of the moon around the earth.

However, if the earth had a year of 360 days per year (= earth's orbital speed of 30.22379 km/s) the moon would now automatically have a 30 day lunar month without changing the speed of the orbit of the moon!

So why did early civilizations around the world use calendars with months of 30 days and years of 360 days? These calendars seemed to function well until sometime in the 8th century BC when suddenly it became necessary to change them. Most civilizations around the world began to modify their calendars to allow for 5 extra days for the year and 6 fewer days for a lunar year. A lunar year is 12 full months; a modern lunar year is 354 days (12 months x 29.5 days).

Now, I'm not interested in the religious aspect of this. However I was wondering if (1) his calculations would be correct assuming that the earth and moon had a faster orbit, and (2) what possible non-supernatural mechanism could conceivably cause a rapid shift (astronomically speaking) in orbital velocity/period consistent with this guys theory?

Squashed
2006-Jun-22, 12:33 PM
...(2) what possible non-supernatural mechanism could conceivably cause a rapid shift (astronomically speaking) in orbital velocity/period consistent with this guys theory?

There were several very large Earth impacts with meteors and if one was a direct hit in the tangential vector of the Earth's orbit then that would slow down the Earth's orbital speed and cause the Earth to "fall" in its orbit.

If we know the mass and orbital velocity of the Earth and we know the velocity difference required: 0.433792 km/s; then we should be able to calculate the momentum of the impact-object required to result in what we are looking for.

Since momentum is mass times velocity we can either have a very large slow object or a small very fast object or somewhere in between.

Tog
2006-Jun-22, 12:47 PM
My layman's understand of this says, nope. It's wrong. The speed of the Moon's orbit is independant of the Earth's. It's based on distance from one body to the other. For the Earth to orbit in a 360 day year it would have to move closer to the Sun. That wouldn't have any effect on the distance the moon orbits.

See below for corrections, maybe above givine my typing speed.

Eta C
2006-Jun-22, 01:09 PM
Tog is right here. The Earth would have to be in a smaller orbit for its orbital period to be 360 days vice 365. Something that would change that would have been catastrophic (of course, that's probably what the advocate believes as he's using it to justify Biblical ideas.)

There is another, equally unlikely, way to get a 360 day year. If the Earth's rotation took 24.35 hours instead of 24 you'd have only 360 days in the same 8766-hour year. That's not the one proposed by the link from the OP, however, so it's not entirely relevant.

antoniseb
2006-Jun-22, 01:15 PM
The Earth rotational and revolutionary periods are fairly well known, and the causes of change reasonably understood. It is doubtful that there was a significant amount of change in the last 6000 years, but what change there was has been that the Earth's rotation has been slowing down, so previously there were more days in the year. Six thousand years ago the day was 0.1 seconds shorter, so the year seemed to be 30 to 40 seconds longer. So 365.2422 was 365.2426 back then.

korjik
2006-Jun-22, 06:39 PM
If you assume that the calendar was set when we could get an observational accuraccy of 1.5%, then the year is 360 days long. The month was probably set at the same time to be 30 days because it was 1/2 of 60, the favored base for the people who set the calendar and clock for all people since then. I think this is much more likely than the earth changing orbit.

But to answer the topic, I think it would take 2 impacts to change the period of the earth and still leave the orbit circular. An interesting exercise would be to find the orbital period for a circular orbit at perihelion distance (that is the closest to sun, right? I usually get them backwards :) ).

Ara Pacis
2006-Jun-22, 07:41 PM
If the orbit was truly circular then there wouldn't be a perihelion, right?

What I found interesting about that guy's site was that the numbers appeared to calculate correctly. I don't think that it is necessarily true, but it makes you wonder if some ancient astronomer might have done those calculations to explain why the real year varied from a perfect year. Would such an astronomer have been capable of discerning that data and making those calculations?

Forgive me for sounding woo-woo for a moment, but could a tidal effect from a passing mass cause the changed described in the article? I'm not suggesting that Planet X/Nibiru is true, but I wonder if there really was such a myth that inspired someone to make the calculations to describe the fictional event. Maybe it was deemed apocryphal for this reason, by Bad Astronomy type debunkers.

phunk
2006-Jun-22, 08:43 PM
The year hasn't changed, at least not during human history. If it had, how are so many ancient monuments, like stonehenge, aligned to the rising and setting of the sun during the solstice?

korjik
2006-Jun-23, 05:01 PM
My point is that if you had a circular orbit at the current perihelion, and it was a 360 day orbit might be able to figure the kick needed to get a slightly elliptical 365 day orbit.

Of course, then you run into phunk's problem :)

Gillianren
2006-Jun-23, 06:08 PM
As a side note--since I'm no good at the science, here--very few ancient civilizations did have twelve 30-day months, and if they did, they invariably had a few days each year of "filler days," which were not considered part of any month. Assuming, of course, that their calendars were solar, which is of course not universally true. This was not something they all "just developed" at the same time--as I recall, the original Roman calendar had it from the outset, but then Senators and such started adding days to the calendar to celebrate things, and it got a little out of hand, the last year of the old calendar having over 400 days. (That was also, as I recall, a sort of "reset.")

korjik
2006-Jun-23, 07:05 PM
As a side note--since I'm no good at the science, here--very few ancient civilizations did have twelve 30-day months, and if they did, they invariably had a few days each year of "filler days," which were not considered part of any month. Assuming, of course, that their calendars were solar, which is of course not universally true. This was not something they all "just developed" at the same time--as I recall, the original Roman calendar had it from the outset, but then Senators and such started adding days to the calendar to celebrate things, and it got a little out of hand, the last year of the old calendar having over 400 days. (That was also, as I recall, a sort of "reset.")

Yeah. There is a reason it was called the Julian calendar

antoniseb
2006-Jun-23, 07:25 PM
My point is that if you had a circular orbit at the current perihelion, and it was a 360 day orbit might be able to figure the kick needed to get a slightly elliptical 365 day orbit.

Of course, then you run into phunk's problem :)
There would also be a problem with the moon. If something massive enough to alter the Earth's orbit by 1.5% came that close to us, it would mot likely have ejected the moon from its orbit, and at the very last put it into a very elliptical orbit. As it is, we have records going back to about 600 BC that show that the length of the year and length of the month, and schedule of eclipses are all what we'd have expected back then based on no major perturbation.

Gsquare
2006-Jun-26, 04:06 AM
My layman's understand of this says, nope. It's wrong. The speed of the Moon's orbit is independant of the Earth's. It's based on distance from one body to the other. For the Earth to orbit in a 360 day year it would have to move closer to the Sun. That wouldn't have any effect on the distance the moon orbits.

.

Tog; if you think about it you will realize you are mistaken; a change in the lunar distance is not necessary; the author is correct in his calculation.

If you had read the entire article you will see he clearly states that the moon's orbital speed does NOT need to change, only earth's orbital period, and he explains why.

A change in earth's orbital period IS all that is necessary for a change in lunar period. This is because we are dealing with a lunar period (called the synodic period) which goes from one 'new moon' to another and which depends upon the relative position of the sun (WRT the moon) each month.
In a 360 day earth year, since the earth's position WRT the sun is accelerated forward more in its orbit each month, then the synodic lunar month is increased(it takes the moon another 1/2 day to 'catch up to the sun's new position) and it turns out to be an amount which makes it's period exactly 30 days.

You are probably thinking in terms of a lunar period that is calulated WRT the stars, the siderial period. However, that is not the basis of the calandar 'month', certainly not originally, especially in Old Testament.

Read the rest of the article and it will become clear.

I found it very interesting and accurate, especially since I have also done calculations in this regard (many) years ago. I found that it is not even necessay to think in terms of 'changing' the earth's orbital speed artificially; simply 'moving' the sun itself back ten degrees (as recorded in Hezakiah's miracle) in space (while earth continues to orbit) will allow earth (formerly in circular orbit) to acquire an elliptical path, increasing its orbital period by those several days.

G^2

Ara Pacis
2006-Jun-26, 07:10 AM
So, what could cause a change in the sun such as is described by the author? Would it need to be a change in the sun's position or a shift in solar mass within the sphere of the sun? What could cause something of this magnitude?

hhEb09'1
2006-Jun-26, 09:51 AM
I found it very interesting and accurate, especially since I have also done calculations in this regard (many) years ago. I object to his use of 365.2422 days as the time it takes the earth to make one complete circle around the sun. It's actually (http://www.bautforum.com/showthread.php?p=54884#post54884
) 365.2563604 days. :)

Tog
2006-Jun-26, 09:51 AM
Tog; if you think about it you will realize you are mistaken; a change in the lunar distance is not necessary; the author is correct in his calculation.

If you had read the entire article you will see he clearly states that the moon's orbital speed does NOT need to change, only earth's orbital period, and he explains why.

Okay, I see where I goofed. I was looking at it from a sidereal perspective. Keeping the velocity of the orbit fixed and accelerating the Earth I understand that the lunar month would be longer.

I do disagree with "he clearly states" though. Mixing Bible verses in with the math does nothing to clarify the point. At least not to me. Do the math first, then go into how the math supports the statements. Or, make all the statements first, then use the math to explain them.

He also says
By adjusting the speed of the earth around the sun to give us a year of 360 days we automatically end up with a month that equals 30 days (29.96785 days). It just so happens that all ancient calendars had 12 - 30 day months, which equaled 360 days. These ancient calendars also had 1 solar year = 360 days!
Yet the Hebrew Calendar (http://en.wikipedia.org/wiki/Hebrew_calendar#Names_and_lengths_of_the_months)is different, having 12 or 13 months of 29 or 30 days each.
The Chinese Calendar (http://en.wikipedia.org/wiki/Chinese_calendar#Early_history) used a 365.25 day year in 484 BC and uses 12 or 13 months per year.
The Egyptian Calendar did use a 12 month 30 day system, but added 5 days to the end of the year to make it come out closer. This was in 2400 BC.
The Hindu Calendar goes back at least to at least 1400 BC and doesn't eem to be even close to a 12 month system.

So, while I was wrong about the way I thought about it, I still find it very hard to believe that there was a time in history when the Year was exactly 360 days long.

As for the Suin 'moving' 10 degrees, and reshaping the Earth's orbit... Any chance of a place that explains the math on that one?

Gsquare
2006-Jun-26, 02:07 PM
Okay, I see where I goofed. I was looking at it from a sidereal perspective. Keeping the velocity of the orbit fixed and accelerating the Earth I understand that the lunar month would be longer.

I do disagree with "he clearly states" though. Mixing Bible verses in with the math does nothing to clarify the point. At least not to me. Do the math first, then go into how the math supports the statements. Or, make all the statements first, then use the math to explain them.

Hello, Tog;
What he 'clearly stated' was the math in a simplistic sort of way; namely, that the 360-day orbital period results in a 30 day lunar period WITHOUT having to change the moon's orbital velocity.

What he is attempting to find out is: Can the Hezakiah Biblical event where the sun is supernaturally moved back ten degrees account for the apparent change in length of the lunar month and year. (Since the Hebrew year before that time was 360 days).

The Egyptian Calendar did use a 12 month 30 day system, but added 5 days to the end of the year to make it come out closer. This was in 2400 BC.
The Hindu Calendar goes back at least to at least 1400 BC and doesn't eem to be even close to a 12 month system.

So, ...... I still find it very hard to believe that there was a time in history when the Year was exactly 360 days long.

Well, that is a good point; the fact that we don't seem to have a very accurate or consistent historical record complicates things when going back so far.
By the way, the original Hebrew calandar was always 30 day months (and 360 day years). As your link mentioned they did not adopt the Babylonian calandar (using 29/30 days alternately) until 586 BC, well AFTER Hezikiah's miracle which occured in the 8th century BC.

As for the Sun 'moving' 10 degrees, and reshaping the Earth's orbit... Any chance of a place that explains the math on that one?

I had the details way back; locating them now?well, er... if I could ever just get to the attic and clean out all the ....
If you wanted to start on the math you could first find the actual (approximate) distance the sun would have to have been moved to account for the 10 degree change:

1. Use Kepler's 3rd law to get the 'previous' earth orbital radius using a 360 day earth orbital period (assume an original circular orbit); (don't forget to convert to seconds);

2. Then using that radius multiply by the sine 10* to get the distance moved, (assuming it took place at 12 noon, and the sun was moved parallel to the earth's motion but in the exact opposite direction). A little trig never hurt anyone... ;)
It makes a nice project.
In effect the earth continues at the same orbital speed initially but now 'over-shoots' the circular orbit. It starts to slow down due to the extra distance from the sun and returns in an elliptical path.

G^2

Gsquare
2006-Jun-26, 04:46 PM
I object to his use of 365.2422 days as the time it takes the earth to make one complete circle around the sun. It's actually (http://www.bautforum.com/showthread.php?p=54884#post54884
) 365.2563604 days. :)

Hi, hhEb.

You seem to be doing something similar to what Tog did.

The figure you want to use is sidereal time (wrt fixed stars);
The year used for calandars is a tropical year which is 20 minutes less.
Kilopi made that distinction very clear in the 1st post in the link you cited. :)
In any case i think the difference is small enough not to quibble about.

G^2

Gillianren
2006-Jun-26, 06:20 PM
What he is attempting to find out is: Can the Hezakiah Biblical event where the sun is supernaturally moved back ten degrees account for the apparent change in length of the lunar month and year. (Since the Hebrew year before that time was 360 days).

A) Before I'd accept a conclusion based on this, I'd like evidence, including evidence that they didn't realize that their calendar was off.

B) If they took a Babylonian calendar that was already in use, wouldn't that be evidence that their calendar was off and that the year then was (at least approximately) the same length it is now?

C) No, it couldn't. It could, however, be allegorical.

hhEb09'1
2006-Jul-02, 04:07 AM
Read the rest of the article and it will become clear.

I found it very interesting and accurate, especially since I have also done calculations in this regard (many) years ago. I found that it is not even necessay to think in terms of 'changing' the earth's orbital speed artificially; simply 'moving' the sun itself back ten degrees (as recorded in Hezakiah's miracle) in space (while earth continues to orbit) will allow earth (formerly in circular orbit) to acquire an elliptical path, increasing its orbital period by those several days.

What I found interesting about that guy's site was that the numbers appeared to calculate correctly. I don't think that it is necessarily true, but it makes you wonder if some ancient astronomer might have done those calculations to explain why the real year varied from a perfect year. Would such an astronomer have been capable of discerning that data and making those calculations?

Forgive me for sounding woo-woo for a moment, but could a tidal effect from a passing mass cause the changed described in the article? I'd be interested in your opinion now, after the recalculations below.

Hi, hhEb.

You seem to be doing something similar to what Tog did.

The figure you want to use is sidereal time (wrt fixed stars);
The year used for calandars is a tropical year which is 20 minutes less.
Kilopi made that distinction very clear in the 1st post in the link you cited. :)
In any case i think the difference is small enough not to quibble about.Actually, Guy Cramer makes some horrible errors. Quibblers, like me, find them. :)

He merely takes the tropical year (365.2422) (and you're right, he should be using the sidereal year like I said) and subtracts 360 to get the extra 5.2422 days, which he then divides by 12 and adds that (0.43685) to the synodic month (29.531) to get 29.96785. In other words, he figures that the earth is going faster so the moon will take that much more time to "catch up" (not his words exactly, but that is the gist. The figures are his. He ignores the fraction of a month above 12.)

That's nonsense of course. The sidereal month (http://en.wikipedia.org/wiki/Month#Sidereal_month) is 27.321661, and the sidereal year (http://www.bautforum.com/showthread.php?p=54884#post54884) is 365.2563604. (I'm not disagreeing with his values, just using more accurate ones.) That means the number of lunar periods in a year is 13.36874652, about 365/27. There are one-less-than-that synodic periods in a year (because we lose one due to the revolution around the sun), so divide the length of the year by that, and the synodic period equals 29.53058823--in agreement more or less with the figure 29.531 that Guy used.

If we keep the same lunar sidereal period (as Guy says he would do), and perform the same operations as we did above, we find that the synodic period of the moon orbitting an earth with a 360 day year is only 29.56548956. That's almost ten hours shorter than the figure that Guy came up with. That may not seem like very much, but it is less than an hour longer than the current synodic month! It's no longer very close to the thirty days that Guy seems to feel is so important.