Does precession impact meteor shower timing and radiant points?

[gdaniels99]

Does precession impact the date of meteor shower peak activity? Does precession impact the radiant point of a meteor shower?

For instance, the Perseid meteor show peaks each year around August 13 and appears to radiate from a point near the Perseus constellation.

Was this the same in 3100 BC? Or, due to precession, did it peak at a later/earlier time of year and did it appear to radiate from a different point in the sky? If so, when did it peak in 3100 BC and where did it radiate from?

[Hornblower]

Does precession impact the date of meteor shower peak activity? Does precession impact the radiant point of a meteor shower?

For instance, the Perseid meteor show peaks each year around August 13 and appears to radiate from a point near the Perseus constellation.

Was this the same in 3100 BC? Or, due to precession, did it peak at a later/earlier time of year and did it appear to radiate from a different point in the sky? If so, when did it peak in 3100 BC and where did it radiate from?

The radiant's position relative to the background stars would be virtually unchanged, because the parent comet's orbit would not change much. The apparent positions of the stars and the radiant would be shifted in unison by the precession, and the shower would have peaked early in June in the year 3100 BC, provided we back-extrapolate the Gregorian calender to that date.

[gdaniels99]

What's the formula for calculating the date change? Is it one day lost for every 71 years thus going backwards 5000 years you would lose about 70 days? If so, would this mean that 5,000 years ago the Draconids peaked around August 11-12?

[Centaur]

Does precession impact the date of meteor shower peak activity? Does precession impact the radiant point of a meteor shower?

For instance, the Perseid meteor show peaks each year around August 13 and appears to radiate from a point near the Perseus constellation.

Was this the same in 3100 BC? Or, due to precession, did it peak at a later/earlier time of year and did it appear to radiate from a different point in the sky? If so, when did it peak in 3100 BC and where did it radiate from?

Welcome to the discussion group, gdaniels99.

Hornblower is essentially correct. The timing predictions for annual meteor shower peaks generally should be separated by mean sidereal years of 365.256363 dynamical days composed of 86,400 ephemeris (atomic) seconds each. For all dates prior to the shift to the Gregorian calendar in 1582, it is the astronomical and historical custom to utilize the Julian calendar with years averaging 365.25 days. That of course wreaks havoc with the correlations between seasons and months when going well back into BC dates.

It should be noted that the orbital characteristics of meteoroids can alter over time, which could affect timing estimates for dates well in the past. I do not take that latter consideration into account for the relatively short time frame of the meteor shower predictions posted on my website: www.curtrenz.com/astronomical

Without allowing for orbital shifts, I estimate that a peak of the Perseids would have occurred on -3099 JUN 27 at 05 hr UT in the Julian calendar, if that shower actually existed back then. The astronomical year -3099 is the same as the historical year 3100 BC, due to historians not employing a year 0 (zero). Also, our Roman system of months was not used prior to the first millenium BC. Finally, keep in mind that reports of Perseid observations have only been made during the AD era.

[Hornblower]

What's the formula for calculating the date change? Is it one day lost for every 71 years thus going backwards 5000 years you would lose about 70 days? If so, would this mean that 5,000 years ago the Draconids peaked around August 11-12?

I used the equation x/365 = 5110/25800, where x is the number of days by which the date changed, in this case about 72 days. It is only a rough estimate because I ignored the Earth's orbital eccentricity. The shift should be about the same for any shower.

[plphy]

Here's a discussion of the history of Perseid observations, including their shift in the calendar (but basically everything calendar-related has already been said in the thread):

Beech, M.
The Makings of Meteor Astronomy: Part XIV
WGN, Journal of the International Meteor Organization, p. 157-160.
http://articles.adsabs.harvard.edu/f...IMO...25..157B

Bye,
Thomas

[gdaniels99]

I have a follow-up question to this old thread. Here goes:

A Native American site in Georgia called Ocmulgee Mounds has a structure called the Earth Lodge whose door aligns with the rising sun on two days, Feb 22 and Oct. 22. October 22 currently coincides with the peak of the Orionid meteor shower so I'm curious if that's the reason for the solar alignment on this day. Three questions:

1. Would the door of the earth lodge align with the sunrise on October 22 around the year 1000 AD or would precession impact the date of alignment. (based on previous answers I'm guessing the alignment would still happen on Oct. 22. a thousand years ago, correct?)
2. Would the peak of the Orionids still happen around Oct. 22 back then? (Based on previous answers I calculate it would peak 14 days earlier on Oct. 8, correct?)
3. If that's the case then the Taurids, which currently peak on Nov. 5th, would have peaked 14 days earlier on Oct. 22, correct? Thus the alignment of the Ocmulgee Earth Lodge in 1000 AD would have coincided with the peak of the Taurids?

Are my calculations correct or have I messed up somewhere?

Also, what constellation would the sun have risen in on Oct. 22, 1000 AD?

[a1call]

If the door aligns to the sunrise currently on October 22nd, then it would have aligned to it about the same number of days after equinoxes, 1000 years ago. However the actual date might be a day or so off the 22nd. Gregorian calendar is a calculation based calendar that is very accurate but not perfectly accurate. The biggest problem with its use is that it is based on international dateline which is constant while longitude where equinoxes happen at midnight rotate about quarter of a circle (about 5 3/4 hours) each year.
This has caused the spring equinox to fall on march 20th in the western hemisphere, where it used to be 21st, a mere 30 years ago.

Precession would not be a factor here because it is based against background stars and not the sun.

[Hornblower]

I have a follow-up question to this old thread. Here goes:

A Native American site in Georgia called Ocmulgee Mounds has a structure called the Earth Lodge whose door aligns with the rising sun on two days, Feb 22 and Oct. 22. October 22 currently coincides with the peak of the Orionid meteor shower so I'm curious if that's the reason for the solar alignment on this day. Three questions:

1. Would the door of the earth lodge align with the sunrise on October 22 around the year 1000 AD or would precession impact the date of alignment. (based on previous answers I'm guessing the alignment would still happen on Oct. 22. a thousand years ago, correct?)
2. Would the peak of the Orionids still happen around Oct. 22 back then? (Based on previous answers I calculate it would peak 14 days earlier on Oct. 8, correct?)
3. If that's the case then the Taurids, which currently peak on Nov. 5th, would have peaked 14 days earlier on Oct. 22, correct? Thus the alignment of the Ocmulgee Earth Lodge in 1000 AD would have coincided with the peak of the Taurids?

Are my calculations correct or have I messed up somewhere?

Your calculations look good, provided we extend the Gregorian calendar back to 1,000 years ago. As has been pointed out by others, the calendar date for having the Sun at a particular ecliptic longitude stays about the same, within a day or so, because the Gregorian calendar is adjusted to match the tropical year fairly closely. Since the meteor shower radiant stays aligned with the stars, precession does indeed affect the date of the peak.

At those dates the sun is about halfway in latitude between the equator and the Tropic of Capricorn. I don't know whether or not that figured in the choice of when to align the doors.

Also, what constellation would the sun have risen in on Oct. 22, 1000 AD?

Libra

[Hornblower]

I have a follow-up question to this old thread. Here goes:

A Native American site in Georgia called Ocmulgee Mounds has a structure called the Earth Lodge whose door aligns with the rising sun on two days, Feb 22 and Oct. 22. October 22 currently coincides with the peak of the Orionid meteor shower so I'm curious if that's the reason for the solar alignment on this day. Three questions:

1. Would the door of the earth lodge align with the sunrise on October 22 around the year 1000 AD or would precession impact the date of alignment. (based on previous answers I'm guessing the alignment would still happen on Oct. 22. a thousand years ago, correct?)
2. Would the peak of the Orionids still happen around Oct. 22 back then? (Based on previous answers I calculate it would peak 14 days earlier on Oct. 8, correct?)
3. If that's the case then the Taurids, which currently peak on Nov. 5th, would have peaked 14 days earlier on Oct. 22, correct? Thus the alignment of the Ocmulgee Earth Lodge in 1000 AD would have coincided with the peak of the Taurids?

Are my calculations correct or have I messed up somewhere?

Your calculations look good, provided you are extending the Gregorian calendar back a thousand years. As has been pointed out by others, the calendar date for having the Sun at a particular ecliptic longitude stays about the same, within a day or so, because the Gregorian calendar is adjusted to match the tropical year fairly closely. Since the meteor shower radiant stays aligned with the stars, precession does indeed affect the date of the peak.

At those dates the sun is about halfway in latitude between the equator and the Tropic of Capricorn. I don't know whether or not that figured in the choice of when to align the doors.

Also, what constellation would the sun have risen in on Oct. 22, 1000 AD?

Libra

[gdaniels99]

then it would have aligned to it about the same number of days after equinoxes,

Could you say this in a different way. I'm not sure I understand what you mean. thanks.

[gdaniels99]

At those dates the sun is about halfway in latitude between the equator and the Tropic of Capricorn.

Does the sun being halfway in latitude between the equator and Tropic of Capricorn have any special astronomical significance or cultural significance in any cultures around the world (that you know of?) If so, why?

[a1call]

Could you say this in a different way. I'm not sure I understand what you mean. thanks.

The sun (due to earth's rotation around the sun) returns to the same relative position approximately every 365 d 5 h 49 m 30s.

This period is not divisible by a whole day. So the sun will rise marginally off the same direction at any given location in one year. This being marginal, let it be ignored for the current discussion.

So the sun will rise from the same direction at any given local every year on the same day of the year.
The best way to determine the same day of the year, is the number of the days this day occurs after the day in which say Spring equinox is observed.

An alternate way of determining the same day of the year is to look it up on the Gregorian calendar.
The latter way of determination of the same day of the year could be off at some locals by one day.
The main reason for this is that the calculations for the Gregorian calendar are based per locale and if applied globally
Without altering the dateline to the longitude where It is midnight at start of the year will result in one day of error (difference in date of the same day of the year determination from the former method, which is the number of days counted since the equinox.

[gdaniels99]

Perfect. Got it. Thanks.

[gdaniels99]

New question: I just read that Pawnee earth lodges were also utilized as observatories and the smoke hole in the center of the roof was constructed to view certain parts of the heavens - such as the Pleiades.

How could I determine if the Pleiades would be visible any time of the year through the Ocmulgee earth lodge smoke hole? Here's a google map of the Ocmulgee Earth Lodge: http://goo.gl/maps/9PIu The smoke hole no longer exists but it would have been in the exact center of the circular structure. You can see the entrance on the east side of the structure where the sidewalk appears to enter the structure.

I'm using Stellarium and have set the location to Macon, GA and noticed on Oct 22, 1019 AD that the Pleiades are very high in the sky a little after midnight thus I'm pretty sure someone standing in the Earth Lodge looking up would definitely be able to see them...I just want to see if there's a more precise way to determine this.

[a1call]

I couldn't get the coordinates for the location. If you have them then you could put them in a software and input a date and time to see if the above-head constellations match. There are probably much better softwares online but I only know of an iPhone app called "Star Walk" which I think can do this.
Expert members might know of more appropriate tools.

[Hornblower]

If the door aligns to the sunrise currently on October 22nd, then it would have aligned to it about the same number of days after equinoxes, 1000 years ago. However the actual date might be a day or so off the 22nd. Gregorian calendar is a calculation based calendar that is very accurate but not perfectly accurate. The biggest problem with its use is that it is based on international dateline which is constant while longitude where equinoxes happen at midnight rotate about quarter of a circle (about 5 3/4 hours) each year.
This has caused the spring equinox to fall on march 20th in the western hemisphere, where it used to be 21st, a mere 30 years ago.

Precession would not be a factor here because it is based against background stars and not the sun.

The sun (due to earth's rotation around the sun) returns to the same relative position approximately every 365 d 5 h 49 m 30s.

This period is not divisible by a whole day. So the sun will rise marginally off the same direction at any given location in one year. This being marginal, let it be ignored for the current discussion.

So the sun will rise from the same direction at any given local every year on the same day of the year.
The best way to determine the same day of the year, is the number of the days this day occurs after the day in which say Spring equinox is observed.

An alternate way of determining the same day of the year is to look it up on the Gregorian calendar.
The latter way of determination of the same day of the year could be off at some locals by one day.
The main reason for this is that the calculations for the Gregorian calendar are based per locale and if applied globally
Without altering the dateline to the longitude where It is midnight at start of the year will result in one day of error (difference in date of the same day of the year determination from the former method, which is the number of days counted since the equinox.

You appear to have some inaccurate information about the dates and times of the equinox, and in any case I am unable to understand your line of thought.

The dates of the Gregorian calendar were set by Pope Gregory’s astronomers and took effect in February of 1582. The next spring equinox occurred at approximately 2:50 AM March 21 local time in Rome, according to my best estimate by extrapolating back from recent published times. That was midway between leap years, so the long term average time of the equinox was restored to March 21, as the Pope wished. Of course it fluctuates over the short term and it fell in the afternoon of March 20 in 1584, the first leap year after the decree.

The March equinox this year was at 5:14 AM on March 20, Universal Time (UT), which would be the local standard time in London. That made it the evening of March 19 from the central USA west to the International Date Line. Since this is a leap year that is about the earliest the equinox time comes in the 4-year cycle. The time in a leap year comes about 18 hours earlier over the course of a century, so it is clear that the date in UT for leap years has been March 20 for the past century. That 18hr/century shift is what makes the Gregorian correction of omitting three leap years every four centuries necessary.

[a1call]

You appear to have some inaccurate information about the dates and times of the equinox, and in any case I am unable to understand your line of thought.

The dates of the Gregorian calendar were set by Pope Gregory’s astronomers and took effect in February of 1582. The next spring equinox occurred at approximately 2:50 AM March 21 local time in Rome, according to my best estimate by extrapolating back from recent published times. That was midway between leap years, so the long term average time of the equinox was restored to March 21, as the Pope wished. Of course it fluctuates over the short term and it fell in the afternoon of March 20 in 1584, the first leap year after the decree.

The March equinox this year was at 5:14 AM on March 20, Universal Time (UT), which would be the local standard time in London. That made it the evening of March 19 from the central USA west to the International Date Line. Since this is a leap year that is about the earliest the equinox time comes in the 4-year cycle. The time in a leap year comes about 18 hours earlier over the course of a century, so it is clear that the date in UT for leap years has been March 20 for the past century. That 18hr/century shift is what makes the Gregorian correction of omitting three leap years every four centuries necessary.

I will reply here:

http://cosmoquest.org/forum/showthre...orian-Calendar

[gdaniels99]

Here's the results of all my questions in this forum. It's entitled "Archaeoastronomy of the Ocmulgee Earth Lodge." It appears that this structure was aligned with the peak of the Taurid meteor shower 1000 years ago. It just so happens that astronomers have found that this time period was the most active periods of the Taurid shower of the past 2000 years. It also appears there was an impact event around 1014 AD...and this structure was burned around 1015 AD. Seems to match up with the Aztec "myth" that their Fourth Sun ended in 1011 AD due to a flood and the sky falling. A tsunami was, in fact, recorded in the Atlantic in 1014 AD and it appears it was impact related since the Greenland Ice Core shows an ammonium spike. Any feedback will be much appreciated. Here's my research:

http://lostworlds.org/archaeoastronomy-ocmulgee-earth-lodge/