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#11
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Lat/Long and timekeeping system for Mars
A simple timelapse shows the daily day/night cycle within a larger polar day/night cycle - the only possible valid effect of two distinct rotations operating individually and in combination -
https://www.youtube.com/watch?v=pnuLTeHB3yU One rotation is constant via an assumption that the average 24 hour day substitutes for 'constant' rotation thereby leaving the orbital surface rotation, responsible for the Polar day/night cycle, to reflect a response of variable orbital speeds of the Earth. It is painful watching the death throes of the meaningless 'solar vs sidereal' fiction but ultimately the planet's two actual day/night cycles will emerge from behind the pseudo-intellectual noise. The principles of timekeeping for Earth can be applied to Mars with its own equable hours, minutes and seconds, its own calendar framework, its own Lat/Long system and 24 hour AM/PM cycle and even the predictive utility of a RA/Dec framework. |
#12
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 7:48:24 AM UTC-7, Chris L Peterson wrote:
In many contexts, "day" is reasonably assumed to mean "solar day", but I don't see the problem if the context makes it clear what kind of day is under discussion (and the word "day" in isolation is always ambiguous in meaning). Because "day" is ambiguous. If you think that "day" is ambiguous, except in the sense of the ambiguity of "day" versus "night", versus a day and a night together, you've been spending too long behind your telescope and too long in your ivory tower with other astronomers. In technical astronomical jargon, a "sidereal day" is a kind of day. In plain ordinary English, as used by people who are not astronomers, a sidereal day is *not* a day, never was, and never will be. If you are talking to members of the general public, you need to talk to them in their language, not hit them over the head and force them to use yours. So, instead of saying: "When we're thinking about the motions of planets, a period can be defined in a couple of different ways. The "rotational period" of an object in the solar system is the amount of time it takes for the object to complete one turn, or rotate on its axis. We call the rotational period of Earth a "day".. Earth's day (or rotational period) is exactly 23.9345 hours (or, 23 hours, 56 minutes, 4.2 seconds)." they should have put it this way: When we're thinking about the motions of planets, a period can be defined in a couple of different ways. The "rotational period" of an object in the solar system is the amount of time it takes for the object to complete one turn, or rotate on its axis. Earth's day is 24 hours, but because the Earth moves in orbit around the Sun, from one day to the next, the Sun is in a slightly different direction from the Earth. As a result, Earth's day is actually slightly longer than its rotational period. Earth's rotational period is exactly 23.9345 hours (or, 23 hours, 56 minutes, 4.2 seconds). Astronomers call the rotational period of Earth a "sidereal day". Now, the term "sidereal day" is gradually introduced as a technical term used by astronomers, but no flat statement is made that a day, as such, is something different than what the reader thought it was before. John Savard |
#13
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 8:19:44 AM UTC-7, Paul Schlyter wrote:
Simple, isn't it? All you have to think about is to match your selected type of day to the appropriate type of hour. Perhaps. But I think that even though Oriel is a very special case, ordinary people might come away from an attempt to teach astronomy with such brutality - I'm thinking of the phrase "the brutality with which mathematics is... taught to the innocent" - muttering that those astronomers are nuts. In ordinary language, a day is 24 hours, and whatever a period of 23 hours and 56 minutes may be, it is definitely not a day, as it's four minutes short of a day. Whatever you do, don't begin by flatly contradicting the meaning of words in ordinary language - that comes across as making a statement that is *false*: _because statements in a given language are understood by taking the words in them, and replacing them by their meanings_. So it's almost as if "a day is 23 hours and 56 minutes" *becomes* "a solar day is 23 hours and 56 minutes" somewhere between one's eyes and the part of one's brain that actually is aware of reading the sentence, if one is not already an astronomer... I don't know if this makes sense, but it's as close as I can come to explaining this. (Or, perhaps more directly: people expect words in anything they read to mean what they *expect* them to mean - _new_ words, or even new meanings for old words, can be introduced, and used subsequently, but don't expect people to backtrack and put the new meanings in what they've already read.) Therefore, in statements on this matter addressed to the general public, you should begin by using the term "day" only in its ordinary sense of the solar day, and subsequently introduce the term "sidereal day" as a special technical term by astronomers. Failing to do this - failing to come out of one's ivory tower when talking to those outside - is just what leads to confusion like Oriel's, even if most of those so confused simply ignore astronomy from then on, instead of building a whole system of "corrected" astronomy and then advocating for it while all the time blindly refusing to examine one's own original mistaken assumptions and confusion as he does. So I think a careless legitimate astronomer is a little bit to blame for getting him started, although he is now responsible for his own failure to change course and understand what was explained to him wrong once, but which has now been explained to him correctly many times over - by me alone, as well as by others. John Savard |
#14
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 11:56:54 AM UTC-7, Quadibloc wrote:
On Monday, December 3, 2018 at 7:48:24 AM UTC-7, Chris L Peterson wrote: In many contexts, "day" is reasonably assumed to mean "solar day", but I don't see the problem if the context makes it clear what kind of day is under discussion (and the word "day" in isolation is always ambiguous in meaning). Because "day" is ambiguous. If you think that "day" is ambiguous, except in the sense of the ambiguity of "day" versus "night", versus a day and a night together, you've been spending too long behind your telescope and too long in your ivory tower with other astronomers. In technical astronomical jargon, a "sidereal day" is a kind of day. In plain ordinary English, as used by people who are not astronomers, a sidereal day is *not* a day, never was, and never will be. Oops, I didn't break lines. If you are talking to members of the general public, you need to talk to them in their language, not hit them over the head and force them to use yours. So, instead of saying: "When we're thinking about the motions of planets, a period can be defined in a couple of different ways. The "rotational period" of an object in the solar system is the amount of time it takes for the object to complete one turn, or rotate on its axis. We call the rotational period of Earth a "day". Earth's day (or rotational period) is exactly 23.9345 hours (or, 23 hours, 56 minutes, 4.2 seconds)." they should have put it this way: When we're thinking about the motions of planets, a period can be defined in a couple of different ways. The "rotational period" of an object in the solar system is the amount of time it takes for the object to complete one turn, or rotate on its axis. Earth's day is 24 hours, but because the Earth moves in orbit around the Sun, from one day to the next, the Sun is in a slightly different direction from the Earth. As a result, Earth's day is actually slightly longer than its rotational period. Earth's rotational period is exactly 23.9345 hours (or, 23 hours, 56 minutes, 4.2 seconds). Astronomers call the rotational period of Earth a "sidereal day". Now, the term "sidereal day" is gradually introduced as a technical term used by astronomers, but no flat statement is made that a day, as such, is something different than what the reader thought it was before. John Savard |
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 9:52:33 AM UTC-7, Gerald Kelleher wrote:
It is painful watching the death throes of the meaningless 'solar vs sidereal' fiction I am sorry that the concept of the "sidereal day" was initially presented to you in a confusing manner which has led you to be mistrustful of the astronomical profession. I regret that, for some reason, this has rendered you incapable of understanding the facts in this matter when they are carefully explained: that for certain astronomical purposes, since, as Copernicus showed us, the Earth orbits the Sun like any other planet, motions in the Solar System, to be used in calculations, all have to be taken against a single reference which all the planets share, that being the fixed stars, and not the line from the Earth to the Sun. The Equation of Time makes any attempt to work within the system of Tycho Brahe fall flat on its face in excess complexity when sufficient accuracy is required that the fact that the Earth's orbit around the Sun is not a perfect circle has to be taken into account. John Savard |
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Lat/Long and timekeeping system for Mars
On Mon, 3 Dec 2018 10:56:51 -0800 (PST), Quadibloc
wrote: On Monday, December 3, 2018 at 7:48:24 AM UTC-7, Chris L Peterson wrote: In many contexts, "day" is reasonably assumed to mean "solar day", but I don't see the problem if the context makes it clear what kind of day is under discussion (and the word "day" in isolation is always ambiguous in meaning). Because "day" is ambiguous. If you think that "day" is ambiguous, except in the sense of the ambiguity of "day" versus "night", versus a day and a night together, you've been spending too long behind your telescope and too long in your ivory tower with other astronomers. When we discuss "day" in an academic context, in an astronomical context, in any formal context (as is the case here), "day" is most certainly ambiguous without additional clarification. The fact that you seem to think otherwise is worrisome in someone who has always seemed pretty reasonable to me. The page you referenced was crystal clear about its meaning, and quite correct. |
#17
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Lat/Long and timekeeping system for Mars
Here is a new planet with instrumentation sent by humans with the necessity to create a timekeeping system with its own features that are not arbitrary like a leap day correction within a Martian year, a Martian 24 hour day/night cycle anchored to noon with an integer of hours reflecting 15 degrees geography/geometry and all the other things that work so well on Earth.
The group of people who can't manage to grasp that the average 24 hour day has to come first before anything else is timed using equable hours, minutes, seconds or other subdivisions will, in future, represent a regrettable subculture. The first procedure to creating a Lat/Long system for Mars where time and location are fixed as the system is on Earth, is the determination of the average day by anchoring the observation to noon as noon is always symmetrical to the appearance and disappearance of the Sun regardless of hemisphere or season. https://adcs.home.xs4all.nl/Huygens/06/kort-E.html It is sufficient to ascertain the average 24 hour day on Mars even without the creation of a calendar framework in order to keep Martian days fixed closely to the orbital points of Solstices and Equinoxes. Timekeeping on Earth developed in stages, however, it is possible to operate with the natural noon cycle first on Mars by employing the Earth's 24 hour timekeeping system in discerning noon. The original proposal of Huygen's in terms of sunrise/sunset is perhaps one of the better approaches. |
#18
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 11:56:20 AM UTC-8, Gerald Kelleher wrote:
Here is a new planet with instrumentation sent by humans with the necessity to create a timekeeping system with its own features that are not arbitrary like a leap day correction within a Martian year, a Martian 24 hour day/night cycle anchored to noon with an integer of hours reflecting 15 degrees geography/geometry and all the other things that work so well on Earth. https://en.wikipedia.org/wiki/Timekeeping_on_Mars "The average length of a Martian sidereal day is 24 h 37 m 22.663 s (88,642..66300 seconds based on SI units), and the length of its solar day (often called a sol) is 24 h 39 m 35.244147 s (88,775.244147 seconds). The corresponding values for Earth are currently 23 h 56 m 4.0916 s and 24 h 00 m 00.002 s, respectively. This yields a conversion factor of 1.02749125170 days/sol. Thus Mars' solar day is only about 2.7% longer than Earth's." |
#19
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Lat/Long and timekeeping system for Mars
On Mon, 3 Dec 2018 11:56:16 -0800 (PST), Gerald Kelleher
wrote: Here is a new planet with instrumentation sent by humans with the necessity to create a timekeeping system with its own features that are not arbitrary like a leap day correction within a Martian year, a Martian 24 hour day/night cycle anchored to noon with an integer of hours reflecting 15 degrees geography/geometry and all the other things that work so well on Earth. Martian time is likely to be based locally on martian solar time, with periodic leap second corrections to keep it synchronized with the variable rotation rate... just like on Earth. In all technical matters, time on Mars will be the same as time on the Earth, a count of SI seconds. |
#20
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Lat/Long and timekeeping system for Mars
On Monday, December 3, 2018 at 5:23:32 PM UTC-7, Chris L Peterson wrote:
In all technical matters, time on Mars will be the same as time on the Earth, a count of SI seconds. It certainly is true that SI seconds would be used for measures of _interval_ for such things as assigning radio frequencies or specifying the speed of microprocessors. SI seconds, however, don't work very well for _epoch_ as there's a rather odd number of them in a Martian day, so the jury is still out there. John Savard |
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