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This topic is about time.
It is inspired by the vigorous arguments by Spaniard, who arrived in early 2025 with a passionate support of "scientific" time.
There was a brief moment of confusion, as members of the forum grappled with the difference between time at the scale of planets, and time at the scale of atoms.
All of this is happening within the context of General Relativity, which teaches that time slows as gravity increases or velocity increases with respect to the speed of light.
I decided to ask Google's search assistant to consider the question. I hope this analysis will stimulate discussion that sheds light and avoids creating further confusion.
Update: 2025/02/24 - An ideal application for "scientific" time is "Ship's Time". Every vessel traveling away from Earth must maintain it's own time, and that time will be independent of Earth or any other planet. "Scientific time" is perfect for time keeping on such vessels, and in any habitat away from Earth not tied to a planetary body.
Conversation with Gemini
Hi Gemini! Thank you for all your assistance with a great variety of questions. On this occasion, I am hoping to provide some useful information to a (very small) audience. The question is about the history of the word "second" as a measure of time. I am guessing there is a relationship to the nautical compass, but even there I am unsure of the history of the term minute. Do you have anything in your collection about these terms?It's fascinating to trace the history of these time measurements! Here's a breakdown of the etymological journey of "minute" and "second":
The Foundation: Sexagesimal System:
The roots go back to the ancient Babylonians, who used a base-60 (sexagesimal) number system. This system influenced how we divide circles and, later, time.
"Minute": Pars Minuta Prima:The word "minute" originates from the Latin phrase "pars minuta prima," meaning "first small part." This referred to the first division of an hour into 60 parts.
"Second": Pars Minuta Secunda:Similarly, "second" comes from the Latin "pars minuta secunda," meaning "second small part." This signifies the second division, where each minute is further divided into 60 parts.
Connection to Astronomy:These terms were also used in astronomy to divide degrees of arcs. So, you'd have minutes and seconds of arc, reflecting the same division principle.
Claudius Ptolemy's "Almagest" is a key historical text where these divisions were discussed.
Evolution of Timekeeping:While the concept of these divisions existed for a long time, accurately measuring seconds became possible with the development of precise mechanical clocks, particularly in the 16th and 17th centuries.
The development of atomic clocks in the mid 20th century allowed for even greater precision in defining the second.
In essence, the terms reflect a historical system of dividing quantities into smaller and smaller parts, originating from ancient mathematical practices. While there is a connection to the division of arcs, and therefore a connection to things such as nautical navigation, the primary root is from the latin phrases describing the "first small part" and the "second small part" of a whole.With this background, please consider the question: Is a second on a rotating planet such as the Earth properly defined as a part of the daily rotation of the object, divided into 24 hours which are divided into 60 minutes which are divided into 60 seconds. It appears that there are some humans who might wish to define an arbitrary length of time as a 'second'
You've touched upon a very important point about the evolution of timekeeping! Here's a clarification:
Historical Definition:
Historically, the second was indeed tied to the Earth's rotation, defined as 1/86,400 of a mean solar day.
However, the Earth's rotation is not perfectly consistent. It varies slightly, which made this definition inadequate for precise scientific measurements.
Modern Definition:To address this, the second is now defined based on the properties of atoms. Specifically, it's defined as:
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom."This atomic definition provides a much more stable and precise standard.
Why the Change?The need for extremely accurate timekeeping in fields like navigation (GPS), telecommunications, and scientific research drove the shift to an atomic definition.
Therefore, while the historical concept of the second is rooted in the Earth's rotation, the modern, official definition is not.
Arbitrary Definitions:It is true that anyone could make up an arbitrary definition of a second. However, for scientific and technological systems to work together, they must all use the same, standardized definition. This is why the atomic definition is so important.
In summary, while the concept originated from the Earth's rotation, the modern "second" is an atomic measurement.So now we arrive at the heart of the matter. Mars has it's own unique second, and for convenience, astronomers have deferred to the majesty of Mars, to accept it's second as 1/86400 th of the daily rotation (a Sol). Can you find any evidence that the humanly defined atomic "second" is at all useful on Mars? It would appear to me to be wildly inappropriate.
You've highlighted a very important distinction between fundamental scientific definitions and practical, localized applications. Here's a breakdown of how timekeeping works on Mars, and why the atomic second, while fundamental, isn't the primary practical unit:
Key Points:
The "Sol":
On Mars, the "sol" is the primary unit of a day. It's the length of a Martian solar day, which is slightly longer than an Earth day.
For practical purposes, especially for mission operations, it's far more useful to use the sol as the basis for daily activities.
Martian Timekeeping:Scientists working on Mars missions often use a "Martian clock" that is adjusted to the length of a sol. This means that their hours, minutes, and seconds are slightly longer than Earth's.
This is essential for coordinating activities with the Martian day/night cycle.
The Atomic Second's Role:The atomic second, as defined by the caesium-133 atom, remains the international standard unit of time. It's crucial for precise scientific measurements, including:
Navigation: Spacecraft navigation relies on extremely accurate timekeeping.
Communication: Precise timing is essential for transmitting and receiving data.
Scientific research: Many experiments require extremely accurate time measurements.
Therefore, even on mars, when very precise measurements are required, the atomic second is still the base measurement.
Practical vs. Fundamental:While the atomic second is fundamental, it's not always the most practical unit for everyday use.
Just as we use local time zones on Earth, scientists on Mars use a timekeeping system that's tailored to the Martian day.
In essence:The atomic second is the bedrock of precise time measurement, used in critical scientific and technological applications on Mars.
However, for daily operations and to align with the Martian environment, the "sol" and adjusted Martian time are used.Therefore, you are correct in that for the practical application of everyday time keeping on Mars, that using a second derived from the sol, is far more practical than using the earth based atomic second.
Nicely summarized! Thank you!
You're very welcome! I'm glad I could help
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This post is reserved for an index to posts that may be contributed by NewMars members over time.
It will help if members will write a one line summary of what the post is about, after re-reading the post to see what it ended up being about.
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This post is offered in appreciation of Spaniard's support of "scientific" time measurement.
While "scientific" time is inappropriate for use with rotating masses the size of planets, it ** is ** the perfect solution for humans traveling in space ships, or living in rotating habitats in space.
What I like about the use of the Cesium atom to count increments of time is that it will faithfully adjust to relativistic effects as vessels approach the speeds at which those effects become noticeable.
The time that is counted using the "scientific" method may well become known as "Ship's" time.
Obviously, the time on each vessel or in each habitat will differ from every other ship or habitat, since all will be operating with different velocities and in different gravitational fields.
The day may come when Earth will broadcast a time signal the way Big Ben in London broadcasts the local time. The Earth time will only be meaningful in the context of communications with Earth of course. It will have no significance for humans living elsewhere.
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Because Spaniard made a strong argument for "scientific" time (as compared to planetary time), I've been on the watch for news about scientific time. The article at the link below reports on NASA advances in time keeping in space.
https://www.jpl.nasa.gov/news/working-o … s-mission/
The article reports on the successful test of a Deep Space Atomic clock, and the upcoming Clock-2 that will fly to Venus in 2028 (if all goes well).
Built by NASA’s Jet Propulsion Laboratory in Southern California, the Deep Space Atomic Clock is an ultra-precise, mercury-ion atomic clock encased in a small box that measures about 10 inches (25 centimeters) on each side – roughly the size of a toaster. Designed to survive the rigors of launch and the cold, high-radiation environment of space without its timekeeping performance degrading, the Deep Space Atomic Clock was a technology demonstration intended to carry out technological firsts and fill critical knowledge gaps.
The NASA clock was reported to be 10 times more accurate that GPS clocks. GPS clocks (apparently) have to be updated twice a day from a master clock on Earth. A space probe far from Earth will need to keep it's own time accurately.
I am reminded of the challenges of accurate time keeping on ships at sea on Earth, and reports of shipwreck due to incorrect time keeping by early clocks. Apparently accurate time keeping for celestial navigation is even more important. The article gives examples.
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There is sideral vs solar time right here on Earth, both measured in standard (scientific) seconds, now defined in terms of some physical phenomenon.
Solar time is from noon to noon, 24 standard hours, each 60 standard minutes long, and each of those 60 standard (scientific) seconds long. But the Earth moves in its orbit during that interval, turning through slightly more than 360 degrees, with a finite angle between the two radials from sun to Earth, at noon one day vs noon the next.
Sidereal time is the interval required for the Earth to turn exactly 360 degrees, which is one revolution relative to the "fixed" stars. That is 23 hours, 56 minutes, in terms of the very same standard (scientific) hours and minutes. I don't know it to the nearest standard (scientific) second.
So, the day length on Earth is not simple number, even using standard (scientific) time. Depends upon whether you define a "day" as noon to noon, or as 360 degrees rotation.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The article at the link below is about the interesting idea that time itself may be quantized.
https://interestingengineering.com/scie … heory-link
My interpretation of the report is that while the concept is interesting, it has not been developed far enough so that it can be tested.
it does appear to have promise in the never-ending challenge of merging relativity to quantum mechanics, but my interpretation of the report is that "we aren't there yet".
Looking out a ways, it crossed my mind to wonder what that quantum time increment might be, or if it is relative as so much else in the Universe appears to be.
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Every day I record the location of Mars in the sky as seen from Earth.
The sighting is provided from the location on Earth called Greenwich.
For some reason, it occurred to me today to wonder what time was set in clocks aboard ships, so I asked Gemini.
For whatever reason, I had never heard of the time ball dropping at harbors, to help sailors to note the difference of their chronometers from true UTC time.
There is a teaser at the end, if anyone would like to learn more...
Ship's time reference - Hi Gemini! Thank you for your assistance with numerous questions! This one will (hopefully) be easier than some. It occurred to me to wonder what was the master time kept by mariners from England after invention of the first clock able to keep accurate time on board ships? I assume the time was kept at Universal Time (Greenwich, England) but I've never read that detail in accounts of the use of time for longitude measurement.
It is a fascinating detail that often gets glossed over in historical accounts. You are absolutely right that Greenwich Mean Time (GMT) was the master reference, but the way it was managed on board reveals a clever "two-clock" system that sailors used for centuries.
While a modern traveler might simply change their watch to local time, a navigator in the 18th and 19th centuries strictly maintained two different "realities" of time:
1. The Marine Chronometer (The Master Time)
The ship’s chronometer was never adjusted during a voyage. From the moment the ship left England, that clock was set to Greenwich Mean Time (GMT) and kept in a padded, gimbaled box to protect it from the ship's motion.Why? Longitude is essentially the difference between the time where you are and the time at a fixed reference point (the Prime Meridian at Greenwich). Since the Earth rotates 360
∘
in 24 hours, every hour of difference between your "local noon" and "Greenwich noon" equals 15
∘
of longitude.The Ritual: The chronometer was so precious that only the Captain or the Master usually had the key to wind it, which was done at the exact same time every single day to ensure its "rate" (how much it gained or lost) remained predictable.
2. The Ship’s Bell/Deck Clock (The Local Time)
While the chronometer kept "Greenwich time," the daily life of the crew (meals, watches, and sleep) was governed by Local Apparent Time.Every day at sea, the navigator would perform a "Noon Sight" using a sextant to determine the exact moment the sun reached its highest point in the sky. At that moment, the navigator would shout "Twelve o'clock, Sir!" to the Captain. The Captain would reply, "Make it so," and the ship’s bell would be struck eight times.
The "Adjustment": Unlike the chronometer, the ship’s deck clocks were reset every day at noon to match this local solar time. This meant that on a ship sailing West, the "days" were slightly longer than 24 hours, and sailing East, they were shorter.
Comparison of Timekeeping
Feature Marine Chronometer Ship’s Deck Clock
Reference Greenwich, England (GMT) The Sun (Local Apparent Noon)
Adjustments Never adjusted during the voyage. Adjusted daily at noon.
Purpose Calculating Longitude. Organizing the crew's work/sleep.
Precision High-precision (seconds matter). General (the "bell" system).
Interesting Fact: The Astronomical Day
Until 1925, the Royal Navy and the Nautical Almanac actually used an "Astronomical Day" that began at noon, not midnight. This was because it was easier for navigators; they could take their noon sun sight and start a fresh page in the logbook without the date changing in the middle of their observations!Would you like me to explain how they "checked" the chronometer's accuracy once they reached a distant port, since they couldn't call home to verify the time?
Yes! Please add that detail. It had not occurred to me, but of course that would be important for all travelers, and for that matter, perhaps it would be useful for those on shore.
That is a great observation. Once a ship was at sea for weeks or months, even the finest chronometer would drift by a few seconds. To a navigator, a mistake of just 4 seconds in time could result in a position error of an entire nautical mile.
Checking the clock was vital, and it gave birth to a fascinating piece of maritime infrastructure: the Time Ball.
The Time Ball: The World’s First "Sync"
Since a ship’s chronometer was too delicate to be moved off the ship to an observatory, the "signal" had to come to the ship.Starting in the early 1800s, major ports like Greenwich, Portsmouth, and eventually places like Cape Town and Sydney, installed large, brightly colored balls on high towers or masts near the harbor.
The Process: At exactly five minutes to 1:00 PM, the ball would be raised halfway up the mast. At two minutes to, it would be raised to the very top.
The Signal: At exactly 1:00 PM, the ball would drop.
The Result: Every navigator in the harbor would be standing on deck with their watch in hand, noting the exact error of their chronometer. They didn't reset the clock (which could disturb the mechanism); they simply recorded the "rate" (e.g., "The clock is 12 seconds fast today").
Benefits for Those on Shore
You suspected this would be useful for people on land, and you are absolutely right! Before the mid-19th century, every town in England kept its own "Local Mean Time" based on when the sun was overhead in their specific town. Bristol time was about 10 minutes behind London time.The Railway Influence: As trains began to move faster than horses, "local time" became a disaster for schedules. The railways were the first to adopt "Railway Time," which was essentially Greenwich Mean Time.
Public Utility: People on shore used the harbor Time Balls to set their own pocket watches. Eventually, the signal was sent via telegraph wires across the country. By 1852, the "Greenwich Time Signal" was being pulsed out to every major railway station in Britain.
The "Time Gun"
In some ports, especially those where fog was common and the ball couldn't be seen, they used a Time Gun. A cannon would be fired at a specific time (usually 1:00 PM).A Fun Physics Note: Navigators had to be careful with the Time Gun. Sound travels at about 343 meters per second. If a ship was anchored two miles away from the cannon, the navigator had to subtract nearly 10 seconds from when they heard the bang to account for the "lag" of the sound traveling across the water!
Today, we use GPS satellites which carry atomic clocks to do this work for us, but the "Time Ball" tradition lives on in a very famous way every December 31st. The New Year's Eve Ball Drop in Times Square is actually a direct descendant of these 19th-century maritime navigation signals.
Would you like to know how they managed to find their longitude before the chronometer was invented (using the "Lunar Distance" method), or was it the mechanical side of things that interested you most?
Thank you! I'll publish our correspondence as it is, and wait to see if readers are curious about the next topic you've offered. I'm glad I asked!
It has been an absolute pleasure exploring this with you! It’s a wonderful bit of history that highlights just how much our modern world—from time zones to the New Year’s Eve ball drop—was shaped by the practical needs of sailors trying to find their way home.
I’m delighted to hear you’ll be sharing our correspondence. If your readers do have follow-up questions about the "Lunar Distance" method (the incredibly complex math they used before clocks were reliable), or even the grueling "dead reckoning" they relied on before that, I would be more than happy to dive back into the archives for you.
Safe travels to you and your readers on your historical journey!
Would you like me to provide a brief summary of the "Lunar Distance" method now, just in case you want to include it as a "Coming Soon" teaser for your readers?
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