Physics Discussion Thread

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Re: Physics Thread.

Postby A_Gupta » 18 Mar 2016 10:54

SriKumar wrote:If so, how do we interpret the 'capricon' and 'cancer' yantras? They have the exactly same alignment (albeit different slopes for the gnomon- see below) and will definitely cast the same aligned shadow on their respective dials.

Also, the gnomon of each of the 12 sub-yantras has a different slope to it. What is the significance of this?


Quote: "A particular Rasivalaya instrument becomes operative when the first point of the sign of the zodiac it represents approaches the meridian. At that moment, its 'gnomon' points toward the pole of the ecliptic and its quadrants become parallel to the plane of the ecliptic."

http://www.khagolmandal.com/index.php?o ... &Itemid=15

That explains the different slopes of the gnomons adequately, I think.

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Re: Physics Thread.

Postby Neshant » 18 Mar 2016 11:13

Mort Walker wrote:A nuclear reactor would work, but remember to get torque it would need to use a turbine or motor mechanism which introduces inefficiencies. The device would have to generate enough acceleration to achieve escape velocity..


I was thinking more along the lines of accelerating a space craft in deep space without having material being ejected out the back I.e loss of mass. I.e once the craft is already in space.

How to continuously keep accelerating without losing substantial amounts of mass of the space craft.

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Re: Physics Thread.

Postby rsingh » 18 Mar 2016 19:24

Oh people do not take fiziks that seriously. Watch this video where mohterma is explaining use of Silicon. Watch from 3:39 and decide what she is omitting.

https://www.youtube.com/watch?v=Lr93OsOopvo

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Re: Physics Thread.

Postby SriKumar » 19 Mar 2016 03:27

A_Gupta wrote:
SriKumar wrote:There are 12 zodiac constellations (Leo, Scorpio, Libra etc. etc.) in the sky which form the backdrop of sun as the earth orbits around the sun. This means that the sun 'spends' roughly 1 month 'within' each of these constellations- as seen by a viewer on earth.

The problem is that one cannot see the constellation when the sun is on (too bright, even with sun shades), so ...enter the Rashivalaya yantra (RY).
Sorry for the piece-meal attempts to answer the questions. Without such yantras, the constellation that the sun is in would be determined, e.g., by observation of the stars just before sun-rise.
Yes, Amber G. had mentioned this once. Another way would be (if there was foreknowledge about the location of each constellation of the zodiac in the ecliptic), one could check the constellation at the dead of night and the constellation 'opposite' to that in the ecliptic would be the one sun is in.

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Re: Physics Thread.

Postby SriKumar » 19 Mar 2016 03:39

A_Gupta wrote:
SriKumar wrote:If so, how do we interpret the 'capricon' and 'cancer' yantras? They have the exactly same alignment (albeit different slopes for the gnomon- see below) and will definitely cast the same aligned shadow on their respective dials.

Also, the gnomon of each of the 12 sub-yantras has a different slope to it. What is the significance of this?


Quote: "A particular Rasivalaya instrument becomes operative when the first point of the sign of the zodiac it represents approaches the meridian. At that moment, its 'gnomon' points toward the pole of the ecliptic and its quadrants become parallel to the plane of the ecliptic."

http://www.khagolmandal.com/index.php?o ... &Itemid=15
That explains the different slopes of the gnomons adequately, I think.
Thanks for the link. I did look it up, but unfortunately, I am still at sea. I do not understand the phrase 'approaches the meridian'. I dont think they mean Greenwich meridian. So, I assume they are talking about the longitude on the celestial sphere at vernal equinox? Not sure what is meant by a constellation 'approaching a meridian'.

I am positing that the rashivalaya yantras are designed for use during daytime only, so I am trying to work it out based on solar observations only. I am not sure how someone can know 'the first point of the sign of the zodiac' during daytime. I am assuming that the phrase 'first point of sign of zodiac' refers to a particular 'first' star in any one of the zodiac constellation, but I may be wrong.
TIA for any clarifications.

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Re: Physics Thread.

Postby sudarshan » 19 Mar 2016 05:00

That's the celestial meridian. It's the great circle joining the zenith, the nadir, the north celestial pole, and the south celestial pole. You'd need some background in spherical trigonometry to understand "great circle," but it's a pretty simple concept to grasp.

The first point of a constellation need not be the first star, but I'm guessing here. It depends on how you define your zodiac. It would be the first point to cross the meridian every day, would be my guess.

In fact, the "zero" coordinate for one of the two "axes" in celestial geometry is the point at which the first point of Aries appears on the day of the vernal equinox.

All this sounds very fancy, but it's just fancy terms for some pretty simple concepts which anybody can grasp, so don't be intimidated by the terminology.

Please note that the current western zodiac is tropical, not sidereal (you can look up these terms, again, they're pretty simple), but what this means is that the way the constellations are currently defined in the western system, there are actually 14 zodiacal signs, not 12. That is, the sun passes through 14 constellations in the year. And the sun dwells in some of these constellations for as long as 45 days, while it dwells in some others for as little as 3 days (in fact, it dwells in Cetus for less than a day).

So somebody born in early December would be classified as being "Sagittarian" by the western zodiac, but the sun will not be in Sagittarius at this time. It will be in a little-known constellation - "Ophiucus," which is to say, the snake charmer.

Indian astronomy/ astrology, on the other hand, is sidereal.

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Re: Physics Thread.

Postby sudarshan » 19 Mar 2016 06:16

SriKumar, interesting that you talk about "how can I tell which constellation the sun is during the day?" One method of course is to look at the night sky exactly (say) 12 hours later and back-calculate.

But this is an issue that I'm fond of ( :) - can one be fond of an issue, unless by issue you mean "suputr" or "offspring")? Because whenever some TFTA western-educated guy sneers at the lunar basis of Indian astrology, the question to ask point blank is - I can tell where the moon is against the stars just by looking. Can you do the same with the sun? That's a great big point in favor of lunar astronomy. Islamic astronomy is lunar, so the day of Ramadan will slip by 11 days every year (with respect to the sun's position), and 33 years later will be back where it started. Indian astronomy goes one step further, in being "luni-solar," with emphasis being on "luni." I.e., the astronomy is lunar, but corrections are thrown in in the form of adhika and kshaya maasas every few years to resynchronize with the sun. So there is not continuous slippage like in the Islamic system.

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Re: Physics Thread.

Postby SriKumar » 19 Mar 2016 06:40

sudarshan wrote:SriKumar, interesting that you talk about "how can I tell which constellation the sun is during the day?" One method of course is to look at the night sky exactly (say) 12 hours later and back-calculate.
Yes, as I mentioned in my response to A_Gupta, if the location of the zodiac constellations are known in advance it is easy to deduce the solar constellation. It is the same constellation one would see in the night sky 6 months out.

Dont want to get too much into detail about calendars but without doubt a luni-solar calender is so much more useful to people than a lunar calendar or a solar calendar. A luni-solar calendar can track seasons ...and therefore, rains, summer, winter, seasonal flooding of rivers- all critical for a farming/agriculture; and to some extent hunters, and possibly for kings planning campiagns- they need to have an idea of the weather for extended campaigns. Lunar calendar cannot be used to track seasons....error accumulates over the years, as you observed.

Added later:
However, having lunar basis for a calendar is surefire way to make daily observations and keep a rigorous track of time- the phase of the moon changes a bit every day and there is a binary difference every 14/15 days- i.e. poornima vs amavasya. Luni-solar calendar catches both- so, sneerers,... beware the prowess of the luni-solar calendar.

About the original question on the rashivalaya yantra....yes, I am familiar (actually, 'was familiar' is more accurate) with coordinate geometry and to a lesser extent with spherical geometry. It is just that one needs a coordinate system to figure out their functioning, and that is not described anywhere that mentions rashivalaya yantras and Jantar mantar. But that is OK, it is for us (those who are interested) to figure it out. This cooridnate system could be a starting point. https://en.wikipedia.org/wiki/Ecliptic_ ... ate_system

The link A_Gupta posted (khagolmandal.com) mentions the RVs as a means to calculate celestial longitude and latitude. But the description is quite thin. I'll see if sense can be made out of it.

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Re: Physics Thread.

Postby sudarshan » 19 Mar 2016 21:12

I figured out how these things can tell you which zodiacal sign the sun is in. It's so simple and so ingenious, and a credit to the builder(s). I can try explaining forever, but a picture being worth a thousand words, pics will work much better, so let me see if I can generate a few.

Yes, the rashivalayas for Cancer and Capricorn will point in the same direction, but their slopes will be different.

You can also use these to calculate celestial longitude and latitude (or in modern terms, Right Ascension and Declination), but you would need to know where true north/ south were (or alternatively, where the ecliptic poles were). But you'd need to know the location of the ecliptic poles to build the device in the first place.

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Re: Physics Thread.

Postby sudarshan » 20 Mar 2016 04:47

In the figure below:

* The blue sphere is the earth, represented in twelve panels as it moves around the sun.

* The magenta circle is the location of Jaipur, India - on the day depicted in each panel, Jaipur will trace the little circle (not a great circle) represented by the magenta curve from midnight to midnight.

* The green line is the axis of rotation of the earth.

* The grey circle is the plane of the ecliptic.

* The light blue line is the normal to the ecliptic, and the intersection points of this line with the celestial sphere are the ecliptic poles.

* In the panels, I kept the sun in a fixed location, moved the earth around it, and then rotated the view such that the earth is again centered. But this will effectively rotate the fixed stars or the zodiac.

* The little blue circle is the tangent plane to Jaipur on the earth, at the point of time where the sun is at its zenith for that particular day.

* Thus, the black line will be the local "UP" direction in Jaipur at noon-time on that day.

* So then, the sun, at noon-time, will be tilted from the "STRAIGHT UP" direction by a certain amount, represented by the angle between the black and yellow lines.

* The slope of each rashivalaya will be the angle between the blue tangent plane and the yellow line.

* The rashivalaya will also point towards the ecliptic pole, which is the intersection of the light blue line with the earth sphere.

* For both Cancer and Capricorn, the direction to which the rashivalaya points will also be true north. But not so for the other signs of the zodiac.

* So if the sun is at its highest point, and is also coincident with the first point of one of the zodiacal signs, then the rashivalaya for that sign will not cast a shadow.

Will elaborate more when I get a chance.

Image

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Re: Physics Thread.

Postby SriKumar » 20 Mar 2016 05:44

Sudarshan
I would like to thank you for the methodical definitions, the level of detail and the figures. This is more than anything I've seen on this topic. If you prefer to elaborate more, as you indicated, that is great; but speaking for myself alone, this ought to be more than sufficient for me to figure it out. Your definitions and explanations build on one another. I'll wade through this step by step. Again, I really appreciate the detailed exposition.

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Re: Physics Thread.

Postby sudarshan » 20 Mar 2016 06:04

Sure saar. If something is wrong or not clear, let me know, I can fix that.

I don't know what they used this device for. You don't really need it to figure out the celestial longitude of an object. Celestial longitude is very simple, really. You have a reference point in the sky. For the modern Right Ascension (RA) coordinate, this is the first point of Aries, and this point will have zero RA. Once the first point of Aries crosses the meridian, we can just time other points in the sky. If some other point crosses the meridian one hour after the first point of Aries, then its RA is one hour. RA is represented in hours, minutes, and seconds. You can of course convert it to degrees if you want, with 24 hours being the same as 360 degrees.

Celestial latitude is the angle between some celestial object and the north celestial pole - NCP (you can use the pole star as a close approximation, but the pole star doesn't exactly coincide with the NCP). This celestial latitude, in modern parlance, is called the Declination. I guess you can use the Rashivalayas in some way for measuring this, but again, I don't see a real need for such a complicated device to measure it.

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Re: Physics Thread.

Postby sudarshan » 20 Mar 2016 06:14

Also, since Jaipur is around 26.9 deg. N, and since the Tropic of Cancer is 23.5 deg. N, the rashivalaya angle for Cancer will be a steep 86.6 deg. (90+23.5-26.9 deg.). Does anyone know if this is really the case? Jaipur happens to be just a little bit north of the Tropic of Cancer. Locations further north will have less steep angles.

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Re: Physics Thread.

Postby A_Gupta » 20 Mar 2016 12:43

sudarshan wrote:I don't know what they used this device for. You don't really need it to figure out the celestial longitude of an object. Celestial longitude is very simple, really. You have a reference point in the sky. For the modern Right Ascension (RA) coordinate, this is the first point of Aries, and this point will have zero RA. Once the first point of Aries crosses the meridian, we can just time other points in the sky. If some other point crosses the meridian one hour after the first point of Aries, then its RA is one hour. RA is represented in hours, minutes, and seconds. You can of course convert it to degrees if you want, with 24 hours being the same as 360 degrees.


They didn't have accurate clocks when this was built.

Thanks for the drawings, they are really good!

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Re: Physics Thread.

Postby nandakumar » 20 Mar 2016 16:18

Eons ago I was taking the Pre-University (12th standard, now) Physics practicals exam. Since college lab typically have only a limited number of apparatuse for each experiment, the choice of experiment for each student is decided by lots. I drew the Simple Pendulum experiment (every student's dream question for practicals). I went about setting the experiment. Either because I didn't have the physical strength to clamp the string (I was all of 4 feet something and weighing 45 kilos) hard enough to keep the length constant or the cork had lost its suppleness the first observation generated a L/TSquare value of 27 or therabouts. Come to think of it even the stop watch could be malfunctioning. I didn't think much about the number. I was only focused on seeing that my second observation was closer to that. But of course it wasn't. But time was short. We were required to generate six observations and write out the procedure and observations etc in 90 mts. So, I started faking the numbers so that L/Tsquared was closer to the initial value of 27. It never occurred to me that the number is an universal constant and not an experiment specific constant that can change with time and place. My friends disabused me of that notion as we came out of the lab. I was sweating and anxious with worry till the results were out. I got a B Plus in Physics but there ended my association with the subject as I majored in statistics in the under graduate programme, later. It is some comfort to know many eminent brains were seized of the problem back then and continue to do so as this article in Scientific American explains.
http://blogs.scientificamerican.com/gue ... -constant/

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Re: Physics Thread.

Postby SriKumar » 20 Mar 2016 17:05

OK, I think I finally understand the basic/approach. The rashivalaya yantras all need to be pointing towards the ecliptic pole, or rather, be aligned with the axis normal to the ecliptic plane (light blue line in your figures), in order to cast a 'perfect shadow'; a 'perfect shadow' would associate it with a specific zodiac constellation.

And achieving this is a problem because the earth has an inclined axis that changes its inclination (relative to the normal to the ecliptic plane) though out the year. To account for this, the slopes of the gnomons have to be adjusted, and also, the North-South alignment of the gnomons have to be varied for them to achieve a specific orientation at specific times of the year, (so as to cast a zero shadow). These times of 'zero shadow' are calibrated to the location of a specific zodiac constellation.

I need to go through this further but atleast now I understand the basis. Again, appreciate the work you put in. (I had posed this question on this thread a couple of years ago as well).

About your question of gnomon of Cancer having a steep slope (and capricon having a shallow one), I think the answer is yes. This picture labels each rashivalaya with its zodiac sign.

Image

The website (http://www.mallstuffs.com/Blogs/BlogDet ... ts%20works) took it from a project done by some undergrads at the Math Dept. in National University of Singapore. They (IMHO) went through a lot of work to figure the workings of various instruments on Jantar Mantar for this project. Full credit to them. Project thesis linked below. See page 58 for original figure plus some commentary.

http://www.math.nus.edu.sg/aslaksen/gem ... mantar.pdf

In the picture below the slopes of the gnomon are clearly visible. Capricon is in right 'column' second from bottom. and Cancer is in the left column, second from bottom (if the NUS project is correct).

Image

As to why the yantras are needed, I am not sure given your explanations. But I would point out that each of these yantras come with a curved 'dial' i.e. a curve face on which the gnomon would cast a shadow if there was not perfect alignment. This 'dial' most likely has a scale on it- though I can not see a scale from the public domain pictures. Perhaps this allowed them to track certain movements beyond the 'binary' observation of an alignment (or lack of it).
Last edited by SriKumar on 20 Mar 2016 17:36, edited 1 time in total.

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Re: Physics Thread.

Postby SriKumar » 20 Mar 2016 17:17

Here is the Rashivalaya yantra 'Satellite view, from google maps i.e. it gives the topview. One can see their alignment. You may possibly need to zoom in. The Capricon and Cancer yantras are aligned and also aligned with the Samrat Yantra on to their right. I think the Samrat yantra (regular sun-dial) will be aligned with earth's axis i.e. true north-south alignment.

https://www.google.com/maps/place/Janta ... be!6m1!1e1

If the yantras were built right :) , and our theories are right :) (just kidding) we can deduce from the shadows which month (and time of the day) the picture was taken.

The sun-dial (Samrat yantra) to the right does not cast a perfect shodow (unfortunately), so it is not yet noon, probably 11:00 am or thereabouts. From the rashivalya yantras, the one with the smallest shadow seem to be the one at bottom right, which is Gemini (again, going by the NUS math project). SO, if the sun is in Gemini, the dates should be around mid-June timeframe.

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Re: Physics Thread.

Postby SriKumar » 20 Mar 2016 17:50

sudarshan wrote:Also, since Jaipur is around 26.9 deg. N, and since the Tropic of Cancer is 23.5 deg. N, the rashivalaya angle for Cancer will be a steep 86.6 deg. (90+23.5-26.9 deg.). Does anyone know if this is really the case? Jaipur happens to be just a little bit north of the Tropic of Cancer. Locations further north will have less steep angles.
Correct me if I am wrong but I would assume Capricon yantra to be the steepest. Sun is in Capricon during winter solstice time, which means that the earth's axis has the maximum tilt of any position in its orbit (for the northern hemisphere). So, the plane of Jaipur i.e. the plane of the ground on which the yantras sit on, would be inclined further away from the sun (than say, during summer solstice). To compensate for this greater incline the gnomon would have to be at a steeper angle to the ground (i.e. plane on which the yantras sit on). So, the capricon yantra should probably be the steepest. This matches that diagram drawn by the NUS students.

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Re: Physics Thread.

Postby sudarshan » 20 Mar 2016 20:26

A_Gupta wrote:They didn't have accurate clocks when this was built.

Thanks for the drawings, they are really good!


Thanks!

But without accurate clocks, measuring celestial longitude isn't going to happen even with this device, right?

SriKumar wrote:Correct me if I am wrong but I would assume Capricon yantra to be the steepest. Sun is in Capricon during winter solstice time, which means that the earth's axis has the maximum tilt of any position in its orbit (for the northern hemisphere). So, the plane of Jaipur i.e. the plane of the ground on which the yantras sit on, would be inclined further away from the sun (than say, during summer solstice). To compensate for this greater incline the gnomon would have to be at a steeper angle to the ground (i.e. plane on which the yantras sit on). So, the capricon yantra should probably be the steepest. This matches that diagram drawn by the NUS students.


No, Cancer would be the steepest. You are right, the sun will be in Capricorn during the winter solstice, and the earth's axis has the maximum tilt from the ecliptic for the northern hemisphere. But this means that the "UP" direction in Jaipur will be inclined more from the sun, and the plane of the ground would be inclined less from the sun. You can see this in the diagram I posted.

Panel Row 2, Column 1 in my diagram shows what happens when the sun is in Cancer - noon-time sun is almost directly overhead, which means the yantra would have a very steep angle, almost 90 deg. For Capricorn, Row 4, Column 1, the noon-time sun is very much inclined from the perpendicular, so the yantra would have a shallow angle.

What puzzles me is the fact that for Cancer, for the location of Jaipur, the yantra would need to have a slope of almost 90 deg., but I don't see this in the photos of the devices.

Edit: This thread is in page 56 now. I accidentally went to the first page, and I saw Rahul M's note on not letting the thread stay more than 2 days, unless it gathered the required steam. Guess it became a steam bomb and kept going. Lots of interest in pissikz in this phodum.

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Re: Physics Thread.

Postby A_Gupta » 20 Mar 2016 22:31

sudarshan wrote:But without accurate clocks, measuring celestial longitude isn't going to happen even with this device, right?


One can measure with respect to reference points in the sky, and over time, get the position of the reference points to a good level of accuracy, I think.

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Re: Physics Thread.

Postby SriKumar » 20 Mar 2016 22:56

sudarshan wrote: You are right, the sun will be in Capricorn during the winter solstice, and the earth's axis has the maximum tilt from the ecliptic for the northern hemisphere. But this means that the "UP" direction in Jaipur will be inclined more from the sun, and the plane of the ground would be inclined less from the sun. You can see this in the diagram I posted.

Panel Row 2, Column 1 in my diagram shows what happens when the sun is in Cancer - noon-time sun is almost directly overhead, which means the yantra would have a very steep angle, almost 90 deg. For Capricorn, Row 4, Column 1, the noon-time sun is very much inclined from the perpendicular, so the yantra would have a shallow angle.

What puzzles me is the fact that for Cancer, for the location of Jaipur, the yantra would need to have a slope of almost 90 deg., but I don't see this in the photos of the devices.
I am not sure I understand the reference plane used for estimating steepness. For me, steepness is the angle of the slope of the gnomon with the horizontal plane i.e. the ground on which the devices are built on. This is the plane tangential to earth surface in your figures, located at Jaipur latitude.

I would estimate the slope of the gnomon at winter solstice (from the horizontal plane) to be 26.9 (i.e. latitude of Jaipur) + 23.5 (inclination of earth's axis relative to normal to ecliptic) = 50.4 degrees. Atleast visually, this roughly matches the slope of the gnomon (relative to ground) for the rashivalaya on the right-side, second from bottom in the picture. Sun would be in capricon in this case.

When sun is in cancer, i.e. summer solstice, sun much more overhead. The angle of the gnomon (w.r.t. horizontal) should be 26.9-23.5 = 3.5 degrees. Atleast visually, this seems to be the case in the rashivalaya marked as cancer in the NUS-generated graphic embedded in my post.

I am not sure if the difference between your calc. and my calc. is merely the reference plane (all my slope calcs are w.r.t. horizontal plane of earth's surface at Jaipur).

For Capricorn, Row 4, Column 1, the noon-time sun is very much inclined from the perpendicular
Agreed.
so the yantra would have a shallow angle.
The slope of the gnomon would have to be at a greater angle w.r.t. ground because the gnomon has to 'rotated more' in order to align with the normal to ecliptic (IMHO).

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Re: Physics Thread.

Postby sudarshan » 20 Mar 2016 23:22

SriKumar wrote:
sudarshan wrote:

For Capricorn, Row 4, Column 1, the noon-time sun is very much inclined from the perpendicular
Agreed.
so the yantra would have a shallow angle.
The slope of the gnomon would have to be at a greater angle w.r.t. ground because the gnomon has to 'rotated more' in order to align with the normal to ecliptic (IMHO).


Ah, I think I see where the misunderstanding is. The gnomon slope is such that the sun lines up with it, not so that the ecliptic pole lines up with it. The gnomon points to the ecliptic pole (by this, I mean the azimuthal orientation). But the slope points to the noon-time sun.

See the figure below.

Image

So if the sun were at the first point of that rashi, and if it were also at its highest point in the sky, then both the azimuthal angle and the slope would be lined up with it. So there would be no shadow for that rashivalaya.

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Re: Physics Thread.

Postby SriKumar » 21 Mar 2016 03:50

sudarshan wrote: The gnomon slope is such that the sun lines up with it, not so that the ecliptic pole lines up with it. The gnomon points to the ecliptic pole (by this, I mean the azimuthal orientation). But the slope points to the noon-time sun.
I think we've arrived the source of the difference.

In your diagram, consider the base side of the right-angled triangle i.e. the side that sits on the ground. The base side has a (roughly) north-south alignment. The right angle of the triangle is at the southern end of the base side in your diagram. In reality, if you look at the pictures of the Rashivalaya yantra, the right angle of the base is at the north end of the base side.

Looking at it differently, if you draw a normal to the hypotenuse of the green triangle in your figure, it will be perpendicular to the ecliptic plane. My position is that the rashi valaya yantras are constructed such that a line normal to hypotenuse will point directly to the sun.

Please see picture of the Samrat yantra and the rashivalaya yantras below. The location of sun, though not visible, can be inferrred as being to the right side of the picture. The right side of the picture is therefore the south direction and the left side is the north. Google maps satellite view also confirms this.

In other words, the 'foot' of the hypotenuse i.e. the spot where where people can walk onto a gnomon is to the south, and the apex of the hypotenuse is to its north. (This is not a great picture but one of the few I could find that shows both the sun-dial (either Samrat yantra or the Rashivalay yantra) AND an indication of the sun location.
Image

Here is a hi-res picture that I did not inline because it is huge.
http://previews.123rf.com/images/meinza ... -Photo.jpg

The location of the shadow in your figure is very interesting. I concede that the triangle as you drew would present a 'zero shadow' condition very effectively. Perhaps more so than the yantras as constructed!! But I also believe (and posit) that the shadow is recorded not on the ground, but on the curved dial that accompanies every gnomon in the rashivalaya yantra. In fact, for the Samrat yantra, that huge triangular structure sitting right next to the Rashivalaya yantras, the curved dial has markings that allows us to track time to an accuracy of less than a minute from the shadow cast by the huge gnomon. (However, I am not sure about the function of an elaborate dial in the RVs). So, the gnomons as oriented would give a 'zero shadow' condition on the dial (in effect).

Added later: Finally, found a picture of the gnomon as I believe is oriented.
Image

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Re: Physics Thread.

Postby sudarshan » 21 Mar 2016 05:43

I see. My basic premise of "zero shadow on the ground" was not the principle behind this device. I'll have to think about that some more then. Yes, you're probably right about the curved dials being the indicators on the yantra.

That also answers my question about why the rashivalaya for Cancer wasn't as steep as I thought it should be. But the Cancer and Capricorn devices would still point in the same direction (since the ecliptic pole would be in the same direction when either of these signs was at the meridian).

Your figure could be very useful in figuring this out. Time out to think then :).

Also, it shouldn't be too hard to create a device like this, now that we know (or can calculate) what directions the individual gnomons should point, and also what the slopes should be - for a given latitude, of course. A cardboard or plywood base with two spirit levels on it in perpendicular directions, to ensure that the device was "on the level," and a magnetic compass so that the Cancer and Capricorn gnomons could be made to point to true North (or South, in the southern hemisphere). Then plant cardboard/ plywood gnomons on this base. It should be easy to see how the device behaves in practice. Could be a great science and learning project for budding astronomers.

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Re: Physics Thread.

Postby SriKumar » 21 Mar 2016 07:16

sudarshan wrote:But the Cancer and Capricorn devices would still point in the same direction (since the ecliptic pole would be in the same direction when either of these signs was at the meridian
And they absolutely do. Just take a look at the google satellite image of Jantar Mantar, Jaipur. You'll see that the (huge) Samrat Yantra is in a north-south axis, and the Cancer and Capricon R-yantras are exactly parallel to the Samrat yantra. All of this is easily visible since they sit side-by-side.

In searching for a close-up of rashivalaya yantra, I found this....markings on the curved dial.
The markings are not on the face of the dial, but on the 'vertical' edge of the face.

Image

A super zoomed-in image is below (very large file, did not inline), it shows markings very clearly. They are tracking the movement before and after a perfect shadow (i.e. high-point of sun) occurrence.

https://upload.wikimedia.org/wikipedia/ ... antra2.JPG
Thanks again for the detailed drawings (seems like it was done in a software). Several things are clear to me now.

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Re: Physics Thread.

Postby sudarshan » 22 Mar 2016 05:46

Interesting. Those markings show numbers which don't seem to be in Devanagiri, more like the Roman renditions of numerals ("1", "2", etc.). So I wonder if they were tacked on in more recent times for the benefit of tourists. The interval between "2" and "3" seems to be divided into 72 equal parts - one twelfth, and then one sixth again.

Thanks again for the detailed drawings (seems like it was done in a software). Several things are clear to me now.


Just Matlab :). I wrote that script two days ago to do those drawings, when I saw your post. All you need to know is the basics - tilt of earth's axis from the ecliptic, and some vector algebra. The rest is Matlab-ka-chamatkar, including the plots.

Which gives me an idea. It should be a cinch to simulate the movement of those shadows. I'll give it a shot, that would throw some light on the matter (no pun intended).

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Re: Physics Thread.

Postby sudarshan » 22 Mar 2016 18:15

And speaking of the basics, the joke is on me. There is a fundamental (though not serious) error in the figures I posted earlier. The zodiac signs should go counterclockwise as seen from the North Pole (top of the figure), not clockwise. I actually got it right the first time, then for some reason switched it around. But the figures are still good for illustrating the concept.

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Re: Physics Thread.

Postby SriKumar » 03 Apr 2016 19:46

1. Well, if you have the time, could you please post the same picture with the corrected constellations. I am planning to use it in a teaching setting (for kids), and something like this is very useful. But if you are pressed for time, I can use the old figure. I can credit 'sudarshan, anonymous internet expert on jantar mantarolgy, and hotshot matlab-ologer'. :) . Have used Matlab aeons ago but mainly for simple regression-type stuff, but not wholesale geometric manipulations on a cosmic scale (which you did, literally :) ).

2. I am beginning to agree with your original premise that the 12 rashi valayas were probably not needed to merely locate the solar constellation. THey had to be doing something much more. The Jai Prakash yantra, a little north of rashi-valaya yantra, meant for sideral observations should be able to do the 'solar constellation location' quite well. See below.

3. Just (about) 50 feet north of the rashivalaya yantras, there is another yantra called 'Jai Prakash' yatra. It is a hemi-spherical cavity sunken into the ground. The surface of the cavity is marble, carved with a grid work of azimuth and altitude lines. It meant to get accurate observations of star locations. It has a 'cross-hair' with a hole suspended on top of the center. One can walk into hemispherical cavity sunken into the ground and visually align the cross-hair with a specific star. Doubtless this will give the location of the constellation clearly (at night of course). Seeing that the location of the 12 constellations were quite well-known, computing the location of the solar constellation from this instrument should be simple, and not require another instrument.

It seems that the elaborate rashivalya yantras need to do something more than just locate the solar constellation. I'll probably revisit this sometime later, too much going on right now, but this is a mystery as to why Raja Jai Singh would go through so much trouble to build these 12 (unless they came first and the Jai Prakash yantras came next).

Pic below shows the cross-hair device in the 'center' suspended over the hemisphere. You can see the steps inside the yantra, meant for people to walk inside and take astronomical observations.

Image

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Re: Physics Thread.

Postby sudarshan » 05 Apr 2016 05:21

SriKumar wrote:1. Well, if you have the time, could you please post the same picture with the corrected constellations. I am planning to use it in a teaching setting (for kids), and something like this is very useful. But if you are pressed for time, I can use the old figure. I can credit 'sudarshan, anonymous internet expert on jantar mantarolgy, and hotshot matlab-ologer'. :) . Have used Matlab aeons ago but mainly for simple regression-type stuff, but not wholesale geometric manipulations on a cosmic scale (which you did, literally :) ).


I can flip those constellations back and post a new figure. You don't have to credit me, this is basic astronomy. But if you feel you have to, then yes, "anonymous internet amateur on astronomy" would be good enough.

Long ago, I put together some routines in Matlab to generate shapes like ellipsoids, etc. and that proves really useful in situations like this - set up an ellipsoid or sphere, set up a tangent plane at some point, etc. etc. Matlab plots even allow you to set up lights and render geometric figures. I can even use that feature to trace the shadows of the gnomons, only I don't entirely trust it, I've seen that feature mess up in some situations. I was trying to do a simple trace myself, but I keep messing up some or the other aspect of it. Let me see if I can finally get that right. If so, it might help to figure out how they used this device.

2. I am beginning to agree with your original premise that the 12 rashi valayas were probably not needed to merely locate the solar constellation. THey had to be doing something much more. The Jai Prakash yantra, a little north of rashi-valaya yantra, meant for sideral observations should be able to do the 'solar constellation location' quite well. See below.

3. Just (about) 50 feet north of the rashivalaya yantras, there is another yantra called 'Jai Prakash' yatra. It is a hemi-spherical cavity sunken into the ground. The surface of the cavity is marble, carved with a grid work of azimuth and altitude lines. It meant to get accurate observations of star locations. It has a 'cross-hair' with a hole suspended on top of the center. One can walk into hemispherical cavity sunken into the ground and visually align the cross-hair with a specific star. Doubtless this will give the location of the constellation clearly (at night of course). Seeing that the location of the 12 constellations were quite well-known, computing the location of the solar constellation from this instrument should be simple, and not require another instrument.

It seems that the elaborate rashivalya yantras need to do something more than just locate the solar constellation. I'll probably revisit this sometime later, too much going on right now, but this is a mystery as to why Raja Jai Singh would go through so much trouble to build these 12 (unless they came first and the Jai Prakash yantras came next).

Pic below shows the cross-hair device in the 'center' suspended over the hemisphere. You can see the steps inside the yantra, meant for people to walk inside and take astronomical observations.



Or maybe, like you pointed out above, it is the crosshair which is the workhorse of the device, not really the shadows at all.

I wish Amber G. were here to guide on this, she'd probably have instantly spotted that "anti-clockwise, not clockwise" issue. But I doubt Amber G. will be coming back any time soon. Oh well.

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Re: Physics Thread.

Postby SriKumar » 05 Apr 2016 06:08

>>But I doubt Amber G. will be coming back any time soon.
Not likely....and for long time...but I have to say I got some good clarifications from you...but then, these questions lead to other questions surface. What to do onlee :((

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Re: Physics Thread.

Postby sudarshan » 07 Apr 2016 02:40

Corrected image below. In my experience, whenever you set out to fix a minor error in something, you will usually introduce some major error. Please let me know if that is the case, and I'll go back to the drawing board (literally).

Image

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Re: Physics Thread.

Postby SriKumar » 07 Apr 2016 07:39

Thanks for the revised drawings. They look great, with the 2 equinoxes and 2 solstices captured in the first column. bahut dhanyavaad.

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Re: Physics Thread.

Postby Bade » 20 Apr 2016 21:34

A nice read with personal anecdotes...
https://www.quantamagazine.org/20150922 ... r-physics/

At a recent dinner, joined by a small coterie of postdocs, Arkani-Hamed drew a pentagram on a napkin. The pentagram, like the amplituhedron, is defined by a finite set of lines crossing at a finite number of points. Arkani-Hamed darkened nine points in the configuration and explained that the first eight of these dots can be placed on a grid. But no matter how fine the grid, the ninth dot always falls between grid points; it is forced to correspond to an irrational number. There is a mathematical proof, Arkani-Hamed observed, that all algebraic numbers can be derived from configurations of a finite whole number of intersecting points and lines. And with that, he expressed a final conjecture, at the end of a long, cerebral day, before everyone else went home to bed and Arkani-Hamed headed to the airport: Everything — irrational numbers, along with particle interactions and the correlations between stars — ultimately arises from possible combinatorial arrangements of whole numbers: 1, 2, 3 and so on. They exist, he said, and so must everything else.

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Re: Physics Thread.

Postby UlanBatori » 26 Apr 2016 06:23

Any experts out there who can tell me where to buy a good 220GHz source that I can plug into a wall socket? Power level of maybe 100 mW? And how much? Also, how to buy an antenna tuned to the same frequency?

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Re: Physics Thread.

Postby member_27581 » 05 May 2016 16:07

https://www.newscientist.com/article/mg ... ack-holes/
By Jacob Aron

IT’S one surprise after another. The detection of gravitational waves announced earlier this year sent ripples through the world of physics. The signal was thought to come from two gigantic black holes merging into one, but now a group says it could have come from something even more exotic – a gravastar.

“An object almost as compact as a black hole, but with no event horizon, will vibrate in almost the same way“
No one is disputing the first detection of gravitational waves. The Laser Interferometer Gravitational-Wave Observatory (LIGO) team announced in February that it had seen these ripples in space-time predicted by Albert Einstein’s theory of relativity (see “How we found them: Inside a giant gravitational wave detector“).

“We’re not trying to say LIGO was wrong,” says Paolo Pani of the Sapienza University of Rome, Italy. But Pani and his colleagues say the signal might not have come from a black hole merger.

That’s because the LIGO signal breaks down into three phases. First there is the inspiral, which tells you two objects are getting closer as they orbit each other, changing the frequency of their gravitational waves. Next, there is the merger itself, in which the signal ramps up in intensity and frequency. Finally there’s the ringdown, a rapid drop-off as the merged black hole settles down and the wave fades.

In particular, this last phase would indicate the formation of a new event horizon, the region of space from which not even light can escape a black hole’s clutches.

“The common view is that when you see this ringdown, that is a signature of the horizon, because only black holes will vibrate in precisely that way,” says Pani. But his team shows there are other possibilities (Physical Review Letters, doi.org/bfrm).

One is a proposed alternative to black holes called a gravastar, a dense ball of matter kept inflated by a core of dark energy. We have never seen one, but all the evidence we have for black holes could also support their existence. A crucial difference is that gravastars lack an event horizon. Instead, photons can get trapped in a circular orbit around the gravastar, called a light ring.

“If an object is almost as compact as a black hole, even if it doesn’t have an event horizon, it will vibrate almost the same way,” says Pani. “The only difference appears at a very late time when the signal is small, so there is a chance LIGO will miss it.”

“Our signal is consistent with both the formation of a black hole and a horizonless object – we just can’t tell,” says B. S. Sathyaprakash of Cardiff University, UK, who is part of the LIGO team. But if we can detect larger black holes merging, or a pair that is closer to us, it should settle the matter, he says. “That’s when we can conclusively say if the late-time signal is consistent with the merged object being a black hole or some other exotic object.”

Ultimately, the black hole explanation is likely to win out, but it is worth double-checking, says Pani. “As scientists, we try to play the devil’s advocate and not believe in paradigms without observational evidence.”

This article appeared in print under the headline “Have we glimpsed a gravastar?”

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Re: Physics Thread.

Postby UlanBatori » 05 May 2016 20:55

gravastar, a dense ball of matter kept inflated by a core of dark energy

M&M

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Re: Physics Thread.

Postby member_27581 » 08 Jun 2016 14:13

UlanBatori wrote:
gravastar, a dense ball of matter kept inflated by a core of dark energy

M&M

^^
UB Ji what is M&M??? pardon this lesser mortal for asking this question..google chacha not of much help in this context. and when it's you one can never be sure about anything..

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Re: Physics Thread.

Postby UlanBatori » 17 Jun 2016 07:07

Physics Gurus must b asleep or what?
The Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration, and the Virgo collaboration have observed a second gravitational wave event.

The observation was made in the early morning hours (UTC) of December 26, 2015. It is smaller than the initial, historic detection made in September 2015, but was also produced by a pair of colliding black holes.

Gravitational waves, or ripples in the fabric of spacetime, carry information about their origins and the nature of gravity that cannot otherwise be obtained. Physicists say the December waves were produced during the final moments of the merger of two black holes—14 and eight times the mass of the sun—to produce a single, more massive spinning black hole that is 21 times the mass of the sun. LIGO estimated the September black holes were 29 and 36 times the mass of the sun.

“It is very significant that these black holes were much less massive than those observed in the first detection,” said Gabriela Gonzalez, LIGO Scientific Collaboration spokesperson. “Because of their lighter masses compared to the first detection, they spent more time—about one second—in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe.”

The signal was detected by both of the twin LIGO detectors located in Louisiana and the state of Washington.

During the merger, which occurred approximately 1.4 billion years ago, a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. :eek: The detected signal comes from the last 27 orbits of the black holes before their merger.


Hope they have a version converted to sound. That is really worth listening to - will keep u awake in terror for weeks if you think about what it is.
Last edited by UlanBatori on 17 Jun 2016 07:13, edited 1 time in total.

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Re: Physics Thread.

Postby UlanBatori » 17 Jun 2016 07:12

UlanBatori wrote:gravastar, a dense ball of matter kept inflated by a core of dark energy
M&M
^^
UB Ji what is M&M??? ..google chacha not of much help in this context. and when it's you one can never be sure about anything..


Googleswara always ominscient onlee. :mrgreen:

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Re: Physics Thread.

Postby member_27581 » 19 Jun 2016 19:40

^^^there must be a special place in hell for jokes like this....


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