Physics Discussion Thread

[SSSalvi]

A lively and interesting discussion.

Does it mean we have to take three different g values ?

g1 (midnight) = g + gs - a small correction due to change in distance from Sun due to Earth's radius
g2 (Morn/Even) = g
g3 ( Midday ) = g - gs + a small correction due to change in distance from Sun due to Earth's radius

[negi]

^ Well yes , I think without using pen and paper one can make a guess that during the morning or evening time the force vector due to pull exerted by the Sun will be perpendicular to the force vector acting on the object due to gravitational pull of the earth . The net resultant will be more than the extreme cases at noon or midnight.

[Amber G.]

A lively and interesting discussion.

Does it mean we have to take three different g values ?

g1 (midnight) = g + gs - a small correction due to change in distance from Sun due to Earth's radius
g2 (Morn/Even) = g
g3 ( Midday ) = g - gs + a small correction due to change in distance from Sun due to Earth's radius

Thanks for comments, but as I said before, I have seen many giving the similar treatment and apparently making the same error (or missing a critical component) shown implicitly in the above quoted post. (No disrespect to the author of the post)

Again: a hint: BOTH at midnight and midday effect due to sun makes a correction which decreases the value of g (IOW s g1 is almost equal to g3 and both are less than g2)

(Another big hint: This is a very well known physics problem, often asked, analyzed in many books, and needs only elementary physics)

I will wait for a while and let someone else put the explanation here. (Check out any physics text book )

(BTW: as said before, the best intuitive answer to the question (why g1 is less than g2) being given I have seen was from Richard Feynman giving the thought behind the mathematics).. (That was my first (or very early) chance to hear Feynman in person answering student's questions and realized how he can make things simple )

[Amber G.]

Comment about Venus Transit - (Check out any reputable source for more details)

In past this was a very important event because it enabled people to calculate the distance between Sun and Earth to a high precision..(which is needed to make all astronomical calculations, even to more precisely calculate the correction to "g" in problem given above ). This is why astronomers made such a big deal about it.

Now since we can bounce radars on sun, we can calculate the value much more accurately and do not have to wait for a Venus transit.

[Amber G.]

....
g1 (midnight) = g + gs - a small correction due to change in distance from Sun due to Earth's radius
<snip>

Another maha hint/comment one can calculate gs here.. (once one knows the mass of sun = about 300000* earth_mass .., radius of earth, and distance of the sun) try to calculate it ..to see if this value is consistent with what I gave before..)

[SSSalvi]

^^^
I think it was decided earlier that we will not consider the Centrifugal force due to Earth's orbit around Sun.
One possibility is the bending of solar gravitational field around earth can cause the effect of solar magnetic g reduction in magnetic shadow area.
Just a andhere me teer.

[Amber G.]

For Venus Transit - May be of interest..

To get the timings use: the following link ... (Just type in your location - may not be needed if you are on mobile device etc)

http://transitofvenus.nl/wp/where-when/ ... sit-times/

App for your iPhone:http://itunes.apple.com/app/venustransi ... 94620?mt=8
Android:
https://play.google.com/store/apps/deta ... Yi50b3YiXQ


general information http://www.transitofvenus.org/

[vijayk]

http://futureinnovation.larc.nasa.gov/v ... afari.html

In the list, first video discusses clean energy... The author basically describes cold fusion but never uses the word. But NASA is researching it ...



They refer to an article about Widom-Larson theory.

http://www.i-sis.org.uk/Widom-Larsen.php

[Amber G.]

New Take on Impacts of Low Dose Radiation

[kasthuri]

Not sure if this has been posted earlier (if so please ignore...)

The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data

Checkpoints throughout the cell cycle allow for DNA repair or apoptosis and decrease the likelihood of aberrations and genomic instability in a dose-dependent manner (27,28).

Elimination of damaged cells by death or proliferation arrest.—Elimination of cells with altered DNA, a crucial defense mechanism (38–42), may occur by apoptosis shortly after irradiation with doses ranging from a few to about 200 mSv. However, this mechanism of death is less important in most cell types at high doses when the number of cell deaths may cause tissue dysfunction.

At less than a few millisieverts, DNA repair is not activated, and mitotic cell death occurs on resumption of proliferation (1,41). For doses higher than 5 mSv, DNA repair is observed—for example, after computed tomographic (CT) scanning (doses of 10–20 mGy) (42).

Senescence is an alternative pathway for eliminating genetically defective cells without sacrifice of functional advantages before cell death (43–45).

[kasthuri]

Also, relevant to the discussion would be the following review article,

CHECKING THE FOUNDATION: RECENT RADIOBIOLOGY AND THE LINEAR NO-THRESHOLD THEORY

Take a careful look at the 'Gene Expression' section and 'Apoptosis' section.

In the case of DNA damage that is difficult to repair, apoptosis may be the primary cellular response, with the
choice being dictated by excessive amounts of singlestranded DNA generated by repeated unsuccessful attempts at DSB repair (Bree et al. 2004).

There are several defense mechanisms apart from the DNA repair. At least in GBM's (glioblastomas) if the ATM pathway is not activated, apoptosis would help in resisting cancer. In light of this, it is not surprising that low dose need not be damaging.

[SriKumar]

....
g1 (midnight) = g + gs - a small correction due to change in distance from Sun due to Earth's radius
<snip>

a hint: BOTH at midnight and midday effect due to sun makes a correction which decreases the value of g (IOW s g1 is almost equal to g3 and both are less than g2)

Alright....I'll give this a shot. I am not sure what common experiment is being referred to in previous posts, but in any case ...ek try maarke dekhte hain. Just to see, I calculated the force exerted between sun & earth (3.52e22 N) and earth & moon(1.98e20 N) using GMm/R^2 [mass of sun, moon and earth = 1.99e30;7.35e22 and 5.97e24 kgs]. The force by Sun is higher by factor of 100 (atleast they are in a similar range). So, I am going to assume that solar effect on earth might be similar to lunar effect on earth. I know for our problem, for simplicity, we assume just sun and earth (no moon).

I am going to suggest that the earth deforms under the influence of solar gravity, just like it does under lunar gravity- which causes tides. If this is correct, there might be an explanation. The earth deforms under the action of moon to yield high tides in a full-moon position at both ends of the earth- the moon side and the opposite. I believe this is due to the earth deforming like an ellipsoid due to lunar gravity. Same thing would therefore occur between sun and earth. The earth would elongate- so two ends would protrude, one on the sun side (noon) and other on the opposite side (midnight). Ends that protrude are farther away from center of mass of earth, and objects at these ends would be lighter- inversely proportional to square of distance. The other two sides of the ellipsoid would squeeze closer to center of earth and objects there would be heavier?

If this line of thought makes sense, let me know and I can take it further. If it does not, I'll sit back and wait for the solution.

[Bade]

I think AmberG wants all of you to use the concept of center-of-mass of Earth-Sun system to calculate the 'g' felt by an object on the earth's surface at different times of the day. The problem can be simplified to a 3 point mass system and consider the effect on the 3rd due to the combination of the first two. That is why he said it can be found in introductory physics books.

[Amber G.]

Sri Kumarji - I will comment on your post with respect to the original problem in next post.. but first, you brought something more interesting ..

This quote brought to my attention a different, but very well known problem which when asked, in my experience, less than 1 in 100 answer correctly.. (Many have trouble accepting/imagining the answer even when explained.)

Given (BTW which is a correct result)

Just to see, I calculated the force exerted between sun & earth (3.52e22 N) and earth & moon(1.98e20 N) using GMm/R^2 [mass of sun, moon and earth = 1.99e30;7.35e22 and 5.97e24 kgs]. The force by Sun is higher by factor of 100 (atleast they are in a similar range)

What is the orbit of moon, as seen from Sun?
(Okay , this is a little different than above, for this we have to calculate the factor between (moon & sun) and (moon & earth)... and earth is much heavier than moon)

We do know, moon goes around earth (27.3 days)
Also Earth goes around Sun (1 year)

A. Does it go in loops? eg:


B. Or does it go like a wave ..


C. Or something else?

If you have not heard the problem before, try to reason it out before looking it up.

[Amber G.]

Kasturi - Thanks for those articles .. you may enjoy popular piece written by a Caltech PhD.. about LNT
Victims Of Irrational Fear, Not Radiation

... Eating a scoop of ice cream is fine, eating a gallon at one time is bad. Jumping off a chair is no big deal; jumping off a cliff is really stupid. The numbers matter. It’s the dose that makes the poison. There is a threshold to everything.

The radiation in those potato chips isn’t going to kill me. Likewise, no one is going to die from Fukushima radiation. Cancer rates are not going to increase in Japan. The disaster wasn’t hidden like the Soviets did, so that people unknowingly ate iodine-131 for two months before it decayed away to nothing. No one threw workers into the fire like lemmings because they didn’t know what to do.

Where do I get off downplaying the effects of the Fukushima disaster? I’ve been studying the environmental effects of radioactive contamination for three decades, working at America’s national labs and nuclear waste repositories. My enduring frustration: the extreme supposition that all radiation is deadly and that there is no dose below which harmful effects will not occur.

This idea, known as the Linear No-Threshold Dose hypothesis (LNT), was adopted in 1959 as the global regulating philosophy and remains entrenched against all scientific evidence. It is an ethical nightmare. And it will destroy Japan’s economy....

Also

Seriously? LNT is not established science, it’s established policy. Ideology and policy are not science. I love Google and Wikipedia, but they don’t take the place of actual research. You need to go back and read the primary documents, review the actual data, read Hermann Mueller’s letters from 1946 and why he chose to ignore certain studies, understand the math of risk analysis, understand the Cold War environment under which LNT was adopted. The job of science is to understand. The job of ideology is to coerce. The people of Japan are not being hysterical, they’re being afraid because we told them to be. Without caring about the consequences. We know better, but sound bites don’t capture the subtleties of this problem.

From:by the same author

[negi]

Srikumar sir neat observation, I never thought on those lines but the question is how much of that elongation (change in Earth's radius) is caused due to Sun's gravitational field vs the centrifugal force due to Earth's rotation ?

[ramana]

S^3, The transit of Venus is the basis of the Mayan Calender. A few years ago was in Cancun and visited the big pyramid, Chichen Itza. Its a huge solar clock with a serpent (ku Kul Kaan) motif on the steps. So at winter and summer solistice the sunlight falls on the serpent motif lighting it up gradually and it appears alive!!!

In the nearby structures they found records of the transit of Venus kept in Mayan script kept for over thousands of years.

[kasthuri]

Kasturi - Thanks for those articles .. you may enjoy popular piece written by a Caltech PhD.. about LNT

Thanks...one thing is for sure: if things were as linear as it was proposed, biology would have been long conquered by math. Linearity is a wishful thinking in biological systems. Linear systems are the easiest systems in the grand scheme of things...may be that's why it is easy to propose it I guess!!:-)

[Amber G.]

S^3, The transit of Venus is the basis of the Mayan Calender. A few years ago was in Cancun and visited the big pyramid, Chichen Itza. Its a huge solar clock with a serpent (ku Kul Kaan) motif on the steps. So at winter and summer solistice the sunlight falls on the serpent motif lighting it up gradually and it appears alive!!!

In the nearby structures they found records of the transit of Venus kept in Mayan script kept for over thousands of years.

Ramanaji - From my impression, though Maryan knew Venus' orbit and time periods quite well (so did Indians, (and Chinese Greeks, Egyptians, Babylonians for that matter ..) I don't think anything was *based* on transit.

Yes, they embodied Venus in the form of the god Kukulkán and in the Dresden Codex, the Maya charted Venus' full cycle, and they had very precise knowledge of its course .. BUT there is no mention of the any Venus transit in Dresden Codex (for example see here) (IOW since they knew the path they can calculate when transit will happen but there was no special significance like Kepler and others gave)

I believe it is just a coincidence that the end of the Mayan Calendar in the year 2012 (Transits of Venus occurs this year)

If you can give a link where one can get more information about the records of the transit of Venus kept in Mayan script ( kept for over thousands of years )...I will be appreciate it. . TIA.

[negi]

^ Gurudev it would be nice if you could post the answer to the weight of the object under influence of Earth and Sun's gravity, that if everyone else has posted their solutions.

[SriKumar]

Sri Kumarji - Given (BTW which is a correct result)

Just to see, I calculated the force exerted between sun & earth (3.52e22 N) and earth & moon(1.98e20 N) using GMm/R^2 [mass of sun, moon and earth = 1.99e30;7.35e22 and 5.97e24 kgs]. The force by Sun is higher by factor of 100 (atleast they are in a similar range)

What is the orbit of moon, as seen from Sun?
(Okay , this is a little different than above, for this we have to calculate the factor between (moon & sun) and (moon & earth)... and earth is much heavier than moon)

We do know, moon goes around earth (27.3 days)
Also Earth goes around Sun (1 year)

A. Does it go in loops? eg:


B. Or does it go like a wave ..


C. Or something else?

If you have not heard the problem before, try to reason it out before looking it up.

No need for the ji, sirjee. I have not heard of this problem before and I'll give it a shot. When I saw the pictures above, from engg. drawing, I knew it is a class for plots called cycloids. So I googled for images of cycloids. Since you had provided the images, I took the license to google for the Images only....nothing else...no earth-sun-moon business. This was a bit more involved than I first realized, but I am not sure I have the right answer.

Here are some calcs anyway. THe center of rotation of the earth-moon system (in proportion to their masses) comes to around 4682 km from center of earth. This is slightly less than radius of earth (6400 km). This is the center of rotation of the earth-moon system. This center should orbit 'cleanly' around the sun i.e. no 'wobble'. Total orbital distance for moon to revolve around earth = 2*pi()*Distance_earth_moon= 3.84e8*2*pi=2.41e9 m. During this timeperiod (27 days), the center of mass translates in a circular orbit around the sun. Length of this distance traversed = 27/365 * circumference of earth-sun orbit. Circumference of earth's solar orbit = 2*pi*distance_earth_Sun = 2*pi*1.50e11= 9.42e11 m. Therefore, distance traversed in 27 days is 27/365*9.42e11 = 6.97e10 m. Comparing 6.97e10 with 2.41e9 m, we see that the circumferential distance of revolution of moon is much less than the distance traversed by their center of mass around sun in 27 days.

In cycloid plots, (cycloids run on flat surfaces whereas orbits are circular- but we can still use cycloids for our discussion), if the center of rotation traverses a distance that is exactly the perimeter of the circle (see picture below), we have a cycloidic path traced by a point on the perimeter. In our case however, the distance that the earth-moon system traverses around SUN is about 29 times more (69/2.41) than the length of the lunar orbit around EARTH. This is not a cycloid then.

http://www.daviddarling.info/images/cycloid.gif
Moon's orbit, as seen from an outside reference point, will be more like the path in the second picture where the particle who's path is traced, sits inside the disc- a curtate cycloid. For sure, the path will not have loops (as in option your 'A'). Either the cycloid will be stretched out 29 times, or, more likely, it will be a curtate cycloid- albeit on a curved surface. This is my best-effort guess. (If I had more time, I would have tried the forces route, force -> velocity -> derive the eqn of motion, but it is a weekday and...).

[negi]

^ Sounds right to me too

In cycloid plots, (cycloids run on flat surfaces whereas orbits are circular- but we can still use cycloids for our discussion

Isn't this very similar to what was known as an epicycloid i.e. path traced by a point on the circumference of a circle that rolls on the periphery of another circle on the outside ?

I think as you have deduced 'A' can be safely ruled out.

[Amber G.]

Moon's orbit, as seen from an outside reference point, will be more like the path in the second picture where the particle who's path is traced, sits inside the disc- a curtate cycloid. For sure, the path will not have loops (as in option your 'A'). Either the cycloid will be stretched out 29 times, or, more likely, it will be a curtate cycloid- albeit on a curved surface. This is my best-effort guess. (If I had more time, I would have tried the forces route, force -> velocity -> derive the eqn of motion, but it is a weekday and...).

Almost but not quite ... It is neither A or B (as most will guess). The orbit is *always* convex. That is, there is no "wave" (or curvature never changes the sign - unlik Cycloid which is not always convex..some parts curve in - some out) Some people have trouble believing that...

It is more a like 12-gon with rounded corners.. more details can be found out .. say in this top google query (when searched for moon orbit around sun..)... or any such source.
http://www.math.nus.edu.sg/aslaksen/tea ... onvex.html
Or lookup Wiki http://en.wikipedia.org/wiki/Orbit_of_the_Moon.. last para - Path of Earth and Moon around Sun

[Amber G.]

Negi - Wrt to the other problem - As I said... It is not "my solution" ..

Almost EVERY introductory physics text book which deal with gravity will have the solution..
I was curious so just check Newton's Principia, and this case was notable enough that Newton showed this with calculation..
The "experiment" I talked about, everyone knows it, it was even mentioned in one of SriKumar's post..

****
If any one still wants to work it out without looking it up.. first answer this question:

Why a gagan-naut (or an astronaut in US) is "weighless" in a space-station?
(Does one simply use GmM/r^2 to calculate his/her weight) ?

Rest is trivial..

[Amber G.]

^^^ Explicitly -
The earth is at "free fall" in its orbit around sun, so what one looks at effect on weight due to this, one should consider NOT gmM/r^2 but the difference between it's vale at the center of the earth and surface.

For mathematical treatment,. see for example
http://en.wikipedia.org/wiki/Tidal_forc ... _treatment

And yes, Sun also causes tide(s)..the effect is about half of moon or about .5*10^(-7) g ..

[vina]

So at winter and summer solistice the sunlight falls on the serpent motif lighting it up gradually and it appears alive!!!.

But the solstices themselves change due to the precession of the earth! In fact, that is the source of the difference between the Julian and Gregorian calendar and the Papal Decree by Pope Gregory that shortened (dont remember the date), by 2 weeks . In fact Orthodox folks celebrate all their festivals two weeks later per the "old" calender.

In fact, the Hindu calender too coincides with the Julian calender and the "Uttarayan" and "Dakshinayan" is fixed to the sideral year per the "old" calendar and is hence invariant and gives the "Ayanamsa" which accounts for the difference with the tropical calendar! After some 20 odd thousand years,the tropical year and the seasons and solstices and equinoxes will coincide with the "Sidearal" calendar, but until then, the two are out of whack.

Unless the Mayan civilizations is quite recent (around 500/600 years old), which I doubt, I don't think that a figurine that lights up on the solstices when that were made will light up similarly today!

[Amber G.]

So at winter and summer solistice the sunlight falls on the serpent motif lighting it up gradually and it appears alive!!!.

But the solstices themselves change due to the precession of the earth! In fact, that is the source of the difference between the Julian and Gregorian calendar and the Papal Decree by Pope Gregory that shortened (dont remember the date), by 2 weeks . In fact Orthodox folks celebrate all their festivals two weeks later per the "old" calender.

In fact, the Hindu calender too coincides with the Julian calender and the "Uttarayan" and "Dakshinayan" is fixed to the sideral year per the "old" calendar and is hence invariant and gives the "Ayanamsa" which accounts for the difference with the tropical calendar! After some 20 odd thousand years,the tropical year and the seasons and solstices and equinoxes will coincide with the "Sidearal" calendar, but until then, the two are out of whack.

Unless the Mayan civilizations is quite recent (around 500/600 years old), which I doubt, I don't think that a figurine that lights up on the solstices when that were made will light up similarly today!

Vinaji - You may not be accurate here..precession of the equinoxes (BTW this has been known to a fairly precise value by Indian - and other - astronomers for thousands of years) has not much to do with where "figurine lights up" at solstices.

Yes, precession changes the location of the vernal equinox relative to the fixed stars but it does not change, say longitude and latitude of a place and the tilt of the earth - relative to sun - etc... (Well, not in a significant way, anyway)

(There are some minor variation, eg nutation (where tilt of earth's axis changes a little over in appox 19 year cycle (18.6 years more precise value - Remember periods of Rahu and Ketu -- ) and changes in physical location of the poles (which varies a few meters over a year - or some times by a minor amount after a big earth-quake).. etc...

Length of a tropical year, tilt of earth's axis etc have virtually remained the same for thousands of years. Nutation is of the order of a few tens of seconds of arc..(wasn't discovered till telescopes were discovered).. much smaller than, say, the apparent diameter of the Sun as seen from earth.

Hope this is helpful.

[vina]

Yes, precession changes the location of the vernal equinox relative to the fixed stars but it does not change, say longitude and latitude of a place and the tilt of the earth - relative to sun - etc... (Well, not in a significant way, anyway)

Well, the precssion period is of the order of 26,000 years. In 2000 odd years, we have gone just 2 weeks out of whack, so there is still quite a way to go when it gets REALLY out of whack by say a couple of months when it will be very noticeable. After all Shankaranti and Pre Christian Winter Solstice / Christmas day.. ( Christians just appropriated pre existing festival and said Jesus was born on that day and conveniently again reborn on Easter / Vernal Equinox another pre christian festival appropriated) is now just 2 weeks apart in the Tropical Calendar and Sideral calendar.

All I am saying is that the Mayan figures will light up on the Tropical Solstice as always (which is currently last week Dec whatever) , but not on the Jan 14 per the invariant sideral calendar (that we use and orthodox folks use as well) that the Mayans would have calculated per their observation of solstice (if they were a 2000 year old civilization). In other words, this "lighting up on the Solstice" works, only because Pope Gregory lopped off 2 weeks out of August and brought the tropical calendar back in sync with the seasons . So because of that, when Ramana goes there on the tropical solstice, he can see the serpents light up on that day. But if Pope Gregory hadn't , and Ramana showed up there on what is today Jan 14th per the old calender, it wouldn't in the same way.

Anyways, there is a good wiki entry on Axial Precession of Earth and a write up of it's effects, including that of the solstices.

[Amber G.]

Yes, precession changes the location of the vernal equinox relative to the fixed stars but it does not change, say longitude and latitude of a place and the tilt of the earth - relative to sun - etc... (Well, not in a significant way, anyway)

Well, the precssion period is of the order of 26,000 years. In 2000 odd years, we have gone just 2 weeks out of whack, so there is still quite a way to go when it gets REALLY out of whack by say a couple of months when it will be very noticeable. After all Shankaranti and Pre Christian Winter Solstice / Christmas day.. ( Christians just appropriated pre existing festival and said Jesus was born on that day and conveniently again reborn on Easter / Vernal Equinox another pre christian festival appropriated) is now just 2 weeks apart in the Tropical Calendar and Sideral calendar.

All I am saying is that the Mayan figures will light up on the Tropical Solstice as always (which is currently last week Dec whatever) , but not on the Jan 14 per the invariant sideral calendar (that we use and orthodox folks use as well) that the Mayans would have calculated per their observation of solstice (if they were a 2000 year old civilization). In other words, this "lighting up on the Solstice" works, only because Pope Gregory lopped off 2 weeks out of August and brought the tropical calendar back in sync with the seasons . So because of that, when Ramana goes there on the tropical solstice, he can see the serpents light up on that day. But if Pope Gregory hadn't , and Ramana showed up there on what is today Jan 14th per the old calender, it wouldn't in the same way.

Anyways, there is a good wiki entry on Axial Precession of Earth and a write up of it's effects, including that of the solstices.

Vinaji - Did you even read what I wrote? (Or your own reference in Wiki)..Some of the statements above are quite silly and shows, in my opinion, lack of understanding about, precession and the difference between Gregorian and Julian calendar .. (To put it mildly, precession of equinox has NOTHING to do with correction made in Gregorian calendar over Julian Calendar, I will explain in the next post but you can look up in any standard source) ...

Your use of "tropical solstice" is agin VERY odd....(Solstice are always tropical, so to speak....)

Precession does NOT change the location of the equator (wrt to cities and towns located on earth).. neither does it change simple facts like days and nights are equal on vernal equinox event , or days are longer in the summer.. etc...

Let me give one analogy .... Ramana's statement was like ..

At noon when sun is the highest in the sky .. I can see sunlight in the valley

(The above statement will be correct, even if people did not know that earth is round)
Then if some one comes out and say ..

If people really knew earth was round, the statement will not be correct...if the venue was in Australia .. .. people see sunlight there in the night..

(Putting it explicitly .. it does not matter if Indian standard time is 5.5 hours ahead of GMT.. local noon is local noon..
(Similarly it does not matter if the sun is in Taurus or Leo, a summer solstice is a summer solstice)

Coming back to correction made by (or in the name of ) Pope Gregory - it simply fixed the length of the year from (365.25 days) to little less than it to match the length of tropical year.(365.242 days) .. ABSOLUTELY no relation to sidereal year which happens to be longer than 365.25 days).

Getting back to Ramana's original post, at summer solstice something particular will light up .. they were not measuring the position of the sun with respect to fixed stars .. (people generally do not see stars in the day anyway) ... neither they were concerned with what time of the day (local) it was in Australia or what calendar system they are using in Rome)

[Amber G.]

^^^ Add to above...

Some Hindu calendars are based on sidereal year (length approx 365.257 days)... (In this type of calendar summer shifts a month in about 2000 years)

Some Hindu calendars (like shak - or "official" Indian calendar) are based on tropical year (length approx 365.242 days).. In these seasons remain fixed wrt to name of the months)

And then, of course, there are Lunar (Islamic) calendars which are based on lunar month (length 29.53 days)

Most astronomers use JDN (Julian day number) to avoid all the confusion, which does not depend on a cycle, it just count the number of days past the reference point. (January 1, 4713 BC)

[SSSalvi]

Precession will change relation between Solar time and Sidereal time. But the internal time reference of both the systems don't change with Gregory's correction. His was an ( very bold and confident ) attempt to see that the inter relationship amongst them does not become very glaring over a period of time. The 12 day adjustment was a one time correction to remove accumulated error over centuries and to see that both the systems do not differ much afterwards was the master stroke of 'on-line' correction of 1 day every leap year. To still fine tune it there is a provision for adding 1 day not after every 100 year but only if the century year is divisible by 400.

Solar angles any way are independent of sidereal time or precession.

[vina]

Precession will change relation between Solar time and Sidereal time. But the internal time reference of both the systems don't change with Gregory's correction.

Exactly. That is why if the Mayans put date XX/XX/0000 as either the solstice or equinox and said 2000 years, okay 2000 * 365 days later, come here again, and you will see the serpents light up , they would have been wrong and dead wrong, because of the precession of the earth. It would have lit up 14 days earlier, ie 2000*365 -14 days earlier. Ramana managed to turn up on the "correct" day, because of Pope Gregory and the corrections made to account for the difference !

Now if the mayans said, come by some xx days after the vernal equinox, rather than 365 days, they would be fine because they were using tropical time.

Solar angles any way are independent of sidereal time or precession.

Indeed yes. That is the reason why the suns' rays continue to fall on the serpent after all those 1000s of years (also I am told in the Jagannath temple where it lights up the doorway on something on certain times of the year) and not on some rock some place else.

[vina]

Vinaji - Did you even read what I wrote? (Or your own reference in Wiki)..Some of the statements above are quite silly and shows, in my opinion, lack of understanding about, precession and the difference between Gregorian and Julian calendar ..

The difference is this. Julian calendar did not account for the precessions and variations in earths orbits that influence. Julian calendar is a mechanical count (ok less accurate) like one of those "atomic clocks" that keep time accurate to a femto second level!

The problem is while that atomic time is accurate in itself , the earth goes out of whack with it and that is why you get blaring well published headlines of correction to those clocks . You can do it because you KNOW that it goes out of whack. If all that the Mayans had was some "mechanical" means to keep time (like a hourglass or just adding 365 days or whatever) and closed their eyes for 2000 years, they would arrive close to 2 weeks late for the solstice by their calculations!

(To put it mildly, precession of equinox has NOTHING to do with correction made in Gregorian calendar over Julian Calendar, I will explain in the next post but you can look up in any standard source) ...

It was done because the Easter started going far away from the vernal equinox and the climate no longer reflected what it must be by the calender! No one adjusted clocks for 2000 years before Gregory!

Your use of "tropical solstice" is agin VERY odd....(Solstice are always tropical, so to speak....)

It is always tropical only if you were on the earth and know of the variations between the sideral and tropical time . Not if you were blind folded or were sitting in a spaceship with an atomic clock and no idea of how the weather or seasons on the earth is/was !

Precession does NOT change the location of the equator (wrt to cities and towns located on earth).. neither does it change simple facts like days and nights are equal on vernal equinox event , or days are longer in the summer.. etc...

True. What it changes though is WHEN it occurs (per true time. "true time" is atomic clock time without the corrections ?)

(Similarly it does not matter if the sun is in Taurus or Leo, a summer solstice is a summer solstice)

But Ramana /Mayan's didn't know it 2000 years ago ! All they knew was adding 365 days for a year ! So Ramana landing up there exactly on the solstice day and not 14 days later is thanks to Pope Gregory and the minute adjustments that keep getting made to the clocks!

[vina]

^^^ Add to above...

Some Hindu calendars are based on sidereal year (length approx 365.257 days)... (In this type of calendar summer shifts a month in about 2000 years)

They will go out of whack.

Some Hindu calendars (like shak - or "official" Indian calendar) are based on tropical year (length approx 365.242 days).. In these seasons remain fixed wrt to name of the months)

This one , time gets corrected , so it wont.

And then, of course, there are Lunar (Islamic) calendars which are based on lunar month (length 29.53 days)

If they are just counting and not adjusting clock, will go out of whack.

Most astronomers use JDN (Julian day number) to avoid all the confusion, which does not depend on a cycle, it just count the number of days past the reference point. (January 1, 4713 BC)

Yes. But the days themselves get corrected for time. So , wont go out of whack, unless they use an atomic clock and just add 23.xxxxxxxxxxxxxxxx hrs every day, in which case, they will go out of whack.

[kasthuri]

Finally...here we go...

It’s official: Neutrinos can’t go faster than the speed of light after all

Also from Gaurdian,

Neutrino researchers admit Einstein was right

[Amber G.]

Solar angles any way are independent of sidereal time or precession.

Very well put. Exactly. That's what I was saying too.

Precession will change relation between Solar time and Sidereal time. But the internal time reference of both the systems don't change with Gregory's correction

SSSalvi - I am a little confused about your use of sidereal vs solar time in the above context.. (May be I am missing your point.. anyway .. see the next sentence)

For example, a sidereal day is 23 hours 56 minutes, while a solar day (ordinary day for us) is 24 hours.. Precession has nothing to do with it...(and difference between them causes no confusion among watch makers)

Precession does (but it is just one of the factors) contributes to difference between sidereal year and tropical year but even the length of a sidereal year (or tropical year, or anomalistic year for that matter) changes over long time.. (It was 365.256363004 in 2000 and, yes it can vary a few minutes from year to year.. even the average length varies over centuries..)

.... attempt to see that the inter relationship amongst them does not become very glaring over a period of time. The 12 day adjustment was a one time correction to remove accumulated error over centuries and to see that both the systems do not differ much afterwards was the master stroke of 'on-line' correction of 1 day every leap year....
Solar angles any way are independent of sidereal time or precession.

Just to add and make it clear, Gregory's attempt was NOT to make interrelationship between sidereal year and tropical year not glaring.. but adjusting the length of tropical year from 365.25 days to more accurate value of
365.2425 days - which is still not vary accurate but close enough)..

In other words, it had NOTHING to do with the length of sidereal year, precession of the equinoxes etc.. it just means that they wanted to correct the length of tropical year by a small amount

The only practical aspect most of the people should worry about precession is that when they say "first point of Aries" instead of "vernal equinox" the sun's position with respect to the fixed stars is not the same as it used to be 2000 years ago when vernal equinox was actually in the constellation of Aries.

It does add up some confusion to astrological charts but as Isaac Asimov once famously said that astrology was so much non-sense that it really does not matter which coordinate system one uses to chart a horoscope.

[SaiK]

so E=MC^2 remains in the text book as is.

[Amber G.]

^^^ Add to above...

Some Hindu calendars are based on sidereal year (length approx 365.257 days)... (In this type of calendar summer shifts a month in about 2000 years)

They will go out of whack.

Depends on what one means by "go out of whack" ( True, one calendar system will go out of whack in relation to another but .....An example...

A sidereal day (23 hrs 56 minutes) is 4 minutes shorter than a ordinary day...Not too many watch users are bothered . we do not "correlate" time with stars but rather than sun...

OTOH astronomers and night-sky watchers (who do all their work when sun is not visible) use sidereal time..(Most observatories display sidereal time in the observation rooms) they do not care for the local (standard) time, rather than the position of the starts.

And then, of course, there are Lunar (Islamic) calendars which are based on lunar month (length 29.53 days)

If they are just counting and not adjusting clock, will go out of whack.

Again depends on what one means "go out of whack".. many do use lunar calendar.... (Yes, seasons will vary wrt to name of the month, but it will be a particular phase of the moon on a particular date..)

Most astronomers use JDN (Julian day number) to avoid all the confusion, which does not depend on a cycle, it just count the number of days past the reference point. (January 1, 4713 BC)

This is clear enough, astronomers just count the number of days from an epoch and do not follow any "calendar" (no months, years etc..) to avoid all the confusion. Point is, if one just reads "Jan 12, 1701" in a historic record, there is lot of confusion if one does not know which calendar system is being used.. Most of the Europe (France etc..) switched to Gregorian calendar in 1582 while India (along with GB) switched in 1752.. (Russia switched in 20th century) ..

(This is similar to when one reads old Hindu Astronomy books and panchangs . they also refered to "gat-kali" to remove the confusion between vikram/saka or other calendar epochs)...

Getting back to original Ramana's observation, in my opinion, there is really no scientific reason to doubt that precession of equinoxes had any significant effect on measuring sun's position with respect to a fixed structure on the earth over all those years.. (To be clear, sky in the night may look different on a summer solstice from that of a past summer solstice, but sun's position and angle wrt to fixed structure will not be all that different)

Hope that information is useful.

[Amber G.]

A few comments... (Hope these clarifies, what I think are a few misconceptions )

Precession will change relation between Solar time and Sidereal time. But the internal time reference of both the systems don't change with Gregory's correction.

Exactly. That is why if the Mayans put date XX/XX/0000 as either the solstice or equinox and said 2000 years, okay 2000 * 365 days later, come here again, and you will see the serpents light up

Again.. precession has absolutely noting to do with it.. if you know (can measure) the length of year(tropical) you use that value, if the value is inaccurate you make correction.. (Ancient Indian (and others too) astronomers knew how to measure the length - for that they did not even have to know about precession of equinoxes) - pretty accurately by using older astronomers data.)... point is when the Mayan saw that thing "light up" they knew it was Summer solstice... It was the way to measure the length of tropical year (rather than other way around).. BTW Indian and other astronomers used essentially the same method to calculate the length of the year..

In other words.. this was the basis of data which enabled Gregory to determine the more accurate value of the tropical year (in-stead the other way)

they would have been wrong and dead wrong, because of the precession of the earth. It would have lit up 14 days earlier, ie 2000*365 -14 days earlier. Ramana managed to turn up on the "correct" day, because of Pope Gregory and the corrections made to account for the difference !

Now if the mayans said, come by some xx days after the vernal equinox, rather than 365 days, they would be fine because they were using tropical time

Again, the "correction", to put it mildly, is not due to "precession of the earth" .. it is just that they have to measure the value of the length of the year..

What is most important, it is because of them (and other astronomers who essentially watched equinoxes etc..)Pope Gregory was able to know that the length of the year was something like 365.2425 days..

Ramana will turn up the "correct day" not because of Pope Gregory but rather ....

The day Ramana will see the thing "light up" WILL be the correct day (by definition) and when people carefully counted, and kept records, how many days passed between these evernts, Pope Gregory was able to know how long he wanted his year to be.

[lakshmikanth]

If anyone is interested in learning General Relativity, here is a course from one of the fields greats (of "Black Hole Wars" fame) Leonard Susskind:

http://www.youtube.com/playlist?list=PL6C8BDEEBA6BDC78D

Also for Quantum Mechanics I found these lecture series by JJ Binney from Oxford very helpful:

http://www.youtube.com/playlist?list=PLB3CF07ACB3DBC849

He is an astrophysicist who has an interesting approach to QM (very direct one at that, if you ask me )