Question about variations of the Sun's path over long periods of time

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Discussion Overview

The discussion revolves around the question of whether shadows cast by the sun on a specific date in 1880 would fall in the same location as they would in 2020, particularly focusing on the implications for a film project. Participants explore various factors that could influence shadow positions over time, including astronomical and temporal considerations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • Some participants suggest that shadows would be in the same spot if the mountain's shape has not changed, while others argue that various factors, such as precession and nutation of the Earth's axis, would cause slight variations.
  • One participant notes that local time discrepancies due to historical changes in timekeeping practices could affect shadow positions, emphasizing the complexity of synchronizing time across different regions.
  • Another participant highlights that the height of the sun in the sky changes throughout the day and year, which would affect shadow lengths and positions.
  • Some contributions mention the influence of atmospheric conditions and the nature of the sun as a circular light source, which could lead to gradations in shadow edges.
  • There is a discussion about the relevance of Kepler's laws of planetary motion in understanding the sun's path, with some participants questioning how applicable they are to the context of shadow casting.
  • One participant points out that while shadows may be close to the same position, they would not be identical due to the Earth's axial tilt and orbital variations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether shadows would be in the exact same location, with multiple competing views regarding the influence of astronomical factors, local time discrepancies, and atmospheric conditions. The discussion remains unresolved.

Contextual Notes

Participants note limitations related to historical timekeeping practices, local time variations, and the complexities of astronomical phenomena that could affect shadow positions.

Who May Find This Useful

Filmmakers, educators in Earth Science and Astronomy, and individuals interested in the interplay between timekeeping and astronomical observations may find this discussion relevant.

  • #31
And I believe the placing of clocks in church towers was not simply a nod to visibility. The more puritanical denominations (in the USA, at least) took a vested interest in people organizing their labors throughout the day to better serve divine purpose. No idle hands you know...
Incidentally until about a decade ago Indianapolis and its environs simply eschewed Daylight Savings Time altogether. Made for interesting phone conference scheduling with folks.
But actually I think the moving the clock back and forth is silly.
 
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  • #32
Vanadium 50 said:
It's not the clock so much, it's the need to synchronize clocks in distant cities. The fact that high noon comes at different times in Dodge City as Tombstone didn't matter as far as I can tell pre-railroad. One clock in the town square and you're pretty much done.
OK, I can see that. It was true to certain extent. But it's also true that the telegraph changed everything. By Civil War time, the telegraph was nearly ubiquitous, and the owner of the town steeple clock used the telegraph to set the clock's minute hand. The choice for the hour hand was a local custom. With no synchronization, the town clock might drift 6 or more hours per year, and the telegraph was much easier than a sextant or a sundial to synch it.

The stories from young Thomas Edison are rich with anecdotes about use of the telegraphs in the 1860s. The big application was not the railroads, or timekeeping, but rather the ability to get news from remote places on the same day as it happened. Edison's first commercial success came when he telegraphed out the headline "20,000 Dead Shiloh" and then sold newspapers providing the details. Consider it the 1860s version of TV or Twitter.
 
  • #33
Time was only critical where ships headed off on long voyages. They needed to calibrate their navigational chronometers to handle the problem of determining longitude. That is why the national sea ports had an astronomical observatory watching the Sun and the stars in meridian transit. At the observatory, a ball was slowly raised up a mast in the minutes before midday, held there, then dropped at midday, when a gun was also fired.

A sundial is accurate to a couple of minutes and served for many years to set the time of church bells and services. That is why there is often a sundial in a churchyard. The bell rung from the local church was sufficient to synchronise clocks and get the townsfolk to work on time. Later the church put a clock in the bell tower.
 

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