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I recently came to know that the Sun rises on a different place in the horizon everyday : https://astronomy.stackexchange.com/q/39670/14624 To me the change in the direction of Sun rise seems significant in certain months, as detailed in the question.

What can I do to ensure that an Idol is always strictly facing the rising Sun?

As an aside, I also wonder based on what were the idols in Asian temples placed. Looks like its a general East direction. I think mostly because the effect of this change in the direction of Sun rise isn't as significant in countries closer to the equator, they got away with it. But how can this be achieved in countries further away from the equator (example Australia)?

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    $\begingroup$ Does the entire room/building have to face East or can it just be the statue? If the latter, you can probably create a motorized pedestal plugged to a small computer (i.e. Arduino) which calculates the necessary rotation each morning. $\endgroup$
    – Wasabi ♦
    Nov 5, 2020 at 23:58
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    $\begingroup$ I would imagine that the idols would be placed on pedestals that could be rotated manually and then place them at the center of the room (or at least not along a wall). Seems a lot more practical. Even if you have to build the building such that there are multiple main entrances, all this is still easier than rotating the entire building or room. $\endgroup$
    – DKNguyen
    Nov 6, 2020 at 0:17
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    $\begingroup$ @Wasabi I have edited the question to be more specific. Just the idol needs to face the rising sun. Motorized pedestals are definitely one solution - I can see a few limitations: Weight of the idol. Cost effectiveness. And will require power be present at all times. $\endgroup$
    – happybuddha
    Nov 6, 2020 at 0:27
  • $\begingroup$ @happybuddha: Those limitations are valid, but I'd be willing to bet that getting a motorized pedestal will be cheaper than constructing an entire building which moves! :p $\endgroup$
    – Wasabi ♦
    Nov 6, 2020 at 0:34
  • $\begingroup$ @DKNguyen For the manual rotation of the pedestal, what sort of a measure could one use. Even though the change in the degree of Sun rise is very small every single day - this is an achievable solution. For small and light weight Idols am envisioning placing an enlarged protractor image at the base of the idol and then manually move it everyday after calculations. At worst, I will have to keep replacing the image every so often. This is still not practicable for large-ish Idols as rotating a large idol by hands only by a certain degree can be challenging. $\endgroup$
    – happybuddha
    Nov 6, 2020 at 0:38

2 Answers 2

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I would imagine that the idols would be placed on pedestals that could be rotated manually and then place them at the center of the room (or at least not along a wall). Seems a lot more practical. Even if you have to build the building such that there are multiple main entrances, all this is still easier than rotating the entire building or room.

This is still not practicable for large-ish Idols as rotating a large idol by hands only by a certain degree can be challenging.

I'm imaginging something like a round horizontal platform sitting on wheels or balls that run in a track. Like a lazy susan. Nothing fancy. The wider the hold, the more leverage you have to turn it. Rather than a platform of enormous diameter to provide such leverage, you could provide slots for a piece of lumber to be inserted to increase the leverage, with multiple points around the platform so multiple people can assist.

It'd be like pushing a truck with multiple people, except it is made to be pushed and is on a surface made to be pushed on, with good handholds so multiple people can assist. And unlike pushing a truck, you are rotating it so you have leverage. Might be more doable than you think.

Micheal Angelo's David weighs 5665kg.

Let's very conservatively assume a coefficient of friction of 0.3, which means the pushing force required is 30% of the object's weight (which equates to a very soft wheel on rough terrain that doesn't roll very well, but I would expect the bearing surfaces for your idol platform would be much harder, smoother, and flatter which should decrease this).

That means that the statue on the rolling platform should require a force of 1699kg to overcome the friction. All other force on top of that just serves to accelerate/move it.

The status's base has a "radius" of 1m so it takes 1699kg-m of torque to rotate. There was a little bit of handwaviness here since I wasn't entirely sure how to translate the force of friction for pushing something with linear motion into the friction torque that must be overcome to rotate it. I think you have to integrate and I don't feel like doing that. But I'm pretty sure the true torque required is actually a lot less since using 1699kg-m basically assumes the entire weight of the statue sits on its perimeter where the most torque is required to move it. Mass located nearer the center of the rotation takes a lot less torque to move. The smaller the horizontal radius you make the rollers underneath the platform, the less more leverage you get and the less torque will be required but you trade off stability. Think about a spinning top: it's tiny point right at the center means very little friction torque but it will easily topple over.

A person can push with a force of 45kg quite easily (I am quite small and can easily lift that with my legs) and uses a lever that is 2m long, then the torque produced by one person is 90kg-m. It would take 20 people to overcome the friction, and any additional force from them would rotate the statue.

Not too unreasonable. And this was assuming what I feel to be a rather high coefficient of friction and light pushing load per person. In reality, it should be quite a bit less than this.

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  • $\begingroup$ A closer to correct frictioni is probaby under 0.1 so you could need less people than that $\endgroup$
    – joojaa
    Nov 6, 2020 at 5:30
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    $\begingroup$ Lighthouses had or have heavy rotating lens mechanisms that sit on a circular mecury bath - can be rotated by hand very easily, low friction and very smooth. $\endgroup$
    – Solar Mike
    Nov 6, 2020 at 5:36
  • $\begingroup$ @SolarMike Ahhh. That's a good idea. It had crossed my mind to float it on water but water just isn't dense enough for your statue to float on unless it's a boat. $\endgroup$
    – DKNguyen
    Nov 6, 2020 at 6:11
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You should have a pedestal, stand, or even the entire room rotating back and forth to face the sunrise if you are not going to accept the sunrise at solstices as a good average. The daily change in the length of the day is the least there.

In such a room you can mark the window with lines indicating the exact azimuth of the sunrise for the almanac.

In mosques the orientation of Mecca is important, but Mecca doesn't vacillate.

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  • $\begingroup$ Would you know, how was the orientation of Mecca determined? For mosques constructed before any sense of longitude and latitude existed, wouldn't the early architects have based the orientation on Sun rise and Sun set? If so, they have probably got it wrong? Even though not wrong by much - but still wrong. No? I guess if we keep increasing the definition of the boundaries of Mecca it will still probably be right. But I have limited knowledge on this - hence the curiosity. $\endgroup$
    – happybuddha
    Nov 6, 2020 at 0:42
  • $\begingroup$ @happybuddha If they got it wrong, who would know? The important thing is that the believers thought it was correct. And (as Bertrand Russell once remarked) the definition of "belief" is "something for which there is no evidence" - if there is evidence, there is nothing left to "believe." $\endgroup$
    – alephzero
    Nov 6, 2020 at 0:55
  • $\begingroup$ @happybuddha There are written accounts of how to use a magnetic compass and astrolabe to find the correct direction for travelers to face Mecca when praying, which date back more than 700 years. Of course today, travelling Muslims just use a cellphone app that works from GPS position data. $\endgroup$
    – alephzero
    Nov 6, 2020 at 1:05
  • $\begingroup$ Almost a thousand years ago using the most rudimentary instruments Persian polymath and great poet, Khayaam measured the earth's orbital time by just observing the sky and stars on cold winter nights from the bottom of a well. $\endgroup$
    – kamran
    Nov 6, 2020 at 19:08

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