Fifteen years of radar reveal Venus’s most basic facts
eos.org
eos.org
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.
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.
https://en.m.wikipedia.org/wiki/International_Atomic_Time
Actually, in Sumer, they used an intercalary month every three years or so, much like the leap year in the Gregorian Calendar.
> 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.
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.
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.
1 - https://manoa.hawaii.edu/exploringourfluidearth/physical/nav...
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, but they refrained from detailing the technique 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.
Is there a name for this that I can google for?
NASA calculated, for instance, that filling the Three Gorges Dam reservoir would lengthen the day by 0.06 microseconds.
Here's as pretty good summary:
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?
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.
My approach for day / night type of questions:
- a soccer ball
- a toilet roll
- the lamp in your phone
Since the "Days" seemed to last forever, I used to joke "Are we measuring project progress in Venusian days? Those are like 243 days per regular day"
The 3 minute difference comes from not seeing the atmosphere as part of the planet.
Wow! How much of this hits the atmosphere/surface of Venus. Is this the amount of energy output from the Radio Telescope or that hits the surface.
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.
Wow, that is such a trippy sentence to sink in :)
[1] https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.ht...