Having each day be 3 minutes longer/shorter than the previous one is pretty crazy, even if it's mitigated by the fact that 1 Venusian day is ~243 Earth days.
That really makes me wonder how timekeeping would work for civilizations that evolved on planets with variable day length. Earth has variable periods of sunlight depending on latitude, but Earth's day length itself is relatively constant.
Earth already has this problem. Years aren't consistent both because the number of rotations don't evenly go into a single revolution, but also because Earth's rotation time is variable. For instance, above normal fresh water accumulation on land will measurably change the length of a day.
Generally, there are two solutions. One is to track absolute time by increasing the clock as necessary to realign the day to the year. There are Earth days with where the last minute of the day is 61 seconds long. Daylight Saving Time makes days with 23 hours or 25 hours. And, of course, leap years add a day. Unfortunately, a lot of software/hardware is built by people with misconceptions about time, like a minute can have only 60 seconds or a day can have only 24 hours.
So, the second solution is to update the system periodically. Computers often poll internet time to update the clock and will jump to the new time. Alternatively, some systems skew the system clock with additional milliseconds per second until it catches up with the time change. As long as the values are valid typical ranges, most software doesn't care about sudden changes.
> Years aren't consistent both because the number of rotations
> don't evenly go into a single revolution, but also because
> Earth's rotation time is variable.
Lots of civilizations have found novel solutions to the fact that the number of days in a year is not an integer. Adding an occasional leap month (Hebrew calendar) or leap day (Gregorian calendar), or just letting the calendar get out of sync with the seasons (Islamic calendar).
However, it should be noted that although the Earth's rotation time is measurably variable, such measurements require precision instruments that have only been available for a bit over a century. Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire.
> Human senses could not notice such small changes over the course of a lifetime or even over the lifespan of an empire.
I don't disagree in this case. But I am continually amazed at how resourceful and technical past civilizations could be.
For instance early polynesian navigators ("wayfinders") could look at patterns in wave refraction across the ocean surface, to locate islands over the horizon [1].
They also memorized the setting and rising positions of hundreds of stars. [1]
Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language.
> Unfortunately, much of this knowledge was lost, as the polynesians did not have a written system of language.
Having a writing system might have been sufficient to prevent the loss, but not necessary. I'd argue the immediate cause was the disappearance of folk songs and similar rituals that encoded this knowledge in the culture.
> In Oceania’s oral culture, narrative was the primary tool to memorize and transmit complex accounts of interconnected voyaging routes through the sea of islands. These accounts would have been replete with their respective star (and sun) courses, with bearings, instructions for seasons for travel, the expected quality of swell, winds, sea marks and other indispensable information for reckoning and island finding. In other words, Oceanic geography was, like Oceanic history, genealogy and all other matters of education, a narrative art, taught and memorized at specialized marae primarily through the recitation of chants.
https://www.tandfonline.com/doi/full/10.1080/00223344.2018.1... (Lars Eckstein and Anja Schwarz, The Making of Tupaia’s Map: A Story of the Extent and Mastery of Polynesian Navigation, Competing Systems of Wayfinding on James Cook’s Endeavour, and the Invention of an Ingenious Cartographic System)
Unfortunately it seems that these particular oral traditions lost their fidelity before the age of audio recording. The introduction of writing systems has preserved much knowledge, but it has also destroyed much knowledge by supplanting other modes of preservation. I'm not even sure which is greater. Most of the utility in the adoption of writing systems is prospective, I think.
Interestingly, modernity may be its own worst enemy in this regard. A friend recently pointed me to this experiment that pitted Memory Palaces against an Australian Aboriginal memorization technique[1] by assigning incoming medical students to three different groups: https://journals.plos.org/plosone/article?id=10.1371/journal... The authors' conclusion was that the aboriginal technique offered substantially superior recall, buttheyrefrainedfromdetailingthetechnique out of fear of cultural insensitivity! sigh Maybe it would have been insensitive, and maybe they did the right thing, but the irony is astounding.
[1] Apropos the navigation theme, the technique seems to be one way Aborigines teach their star charts. In fact, the technique itself seems to encode some cultural knowledge, which is presumably why even providing the details might seem culturally invasive--because such knowledge isn't intended for outsiders, except unless taught by a member.
The general physics concept is moment of inertia. If water is moved uphill, this redistributes some of the Earth's mass further away from the axis of rotation, which increases its moment of inertia. Since the total angular momentum of the Earth is not changed by doing this, the result is a reduction of the angular velocity, in other words lengthening the day.
NASA calculated, for instance, that filling the Three Gorges Dam reservoir would lengthen the day by 0.06 microseconds.
I'm imagining a system where you have two different lengths of time units.
You can have a "scientific second" which is defined by distance and the speed of light. Just like we have now in SI. When the rotation of the planet changes slightly you need to compensate by adding leap seconds every few years for things to sync up. Eventually they will need to add a leap second every day as the earth's rotation slows down. Some planet with high variation would be adding and removing these frequently.
But, you can define a second as 1/86400th of a "day". For most civil purposes you just want to know when an event happened relative to the day/night cycle and the year. In which case the order of events is more important than the precise amount of time between the events. If precision is needed, you can always measure in scientific seconds and convert accordingly. I figure the "civil second" is fine for such a purpose because it's not like living beings can consistently and accurately keep track of time in their heads.
Now for a planet with a rotation as slow as Venus the concept of a "day" is probably meaningless. It would be more like a season of light and darkness. So I suppose you'd just only use scientific seconds and count upwards?
Turns out that this standard already exists. UT1 (and its close cousin UT1R) track Earth's rotation using radio astronomy techniques. The basis for adding leap seconds is the wind up between UTC and UT1.
I agree, we ought to align UTC to UT1 instead of TAI. Doing so is not trivial on a technical level, though. At the very least, the GNSS broadcast time parameters wouldn't support such a revision for decades.
Interesting. Noon is when the sun is highest. I had fun explaining time zones to my son the other day. I think he got lost in my train analogy: If the train travels around the earth at the same speed the earth turns, then it's always noon on the train.
Start the clock at zero and just start counting seconds. The problem only occurs when you are trying to calculate sunrise/set times. Your solar power system doesn't care about leap seconds/days/years. It knows to expect sunrise at 353478515 seconds without regard for human concepts of a particular day or month.
Well I assume the drift based on atmospheric anomalies doesn't tend toward a total delta of +/- 0 over time - or at least we're not accurately accounting for it yet. As such we'd face the same january in summer problem the romans faced right? Slowly midnight will move further and further from the time when you're furthest from the sun.
Because unlike Earth, Venus receives a whole bunch of solar radiation on one hemisphere for months on end.
This drives a substantial temperature differential that causes strong winds. Since a day on Venus is longer than a year on Venus, it doesn't take much for the atmosphere to rotate faster, either.
When it becomes tidally locked, days will be infinitely long. It's far less trippy to think about a tidally locked planet than it is to think about one that is almost tidally locked.
The winds on Venus' surface are actually pretty tame ("light breeze", 1 Beaufort, 0.5 to 1 m/s) [1]. Problem is, that even this very slight wind packs a considerable punch at 92 bars of pressure and is comparable to a category 4 hurricane on Earth in terms of power (i.e. it would roughly translate to about 90 m/s; 325 km/h; 200 mph on Earth).
Yea actually, prior to reading this article I always thought of the atmosphere as a mostly static shell that just sorta floats around planets - it's interesting to consider how, when the wind pushes on a mountain the mountain pushes back (not literally of course) and that can cause subtle variations in day cycle on earth that could be influenced by spikes in externally acquired heat in differing parts of the atmosphere - but it's crazy to think how much more dramatic the effect is on Venus.
But the opposite is the case. The sun will get hotter for the foreseeable future until the earth will also become uninhabitable. And then the sun will expand and swallow Venus and probably also our planet. So if we base the choice only on the expected future intensity of the sun Mars would seem the better choice.
That really makes me wonder how timekeeping would work for civilizations that evolved on planets with variable day length. Earth has variable periods of sunlight depending on latitude, but Earth's day length itself is relatively constant.