What sort of orbit changes (and other things) would it take for "daylight shifting"?

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What sort of orbit changes (and other things) would it take for "daylight shifting"?

Postby gd1 » Fri Aug 10, 2018 11:01 am UTC

By daylight shifting (there's probably a different term out there for it) I mean instead of days having more and less daylight at different times during the year, days having the same amount of daylight all year round but at different times. For example: In position X on the globe somewhere north of the equator the daylight would show from 6 am to 4 pm one day and 7 am to 5pm on some other day. It would always be 10 hours of daylight throughout the year, but it would just change what time it happens. I guess it might be easier if only one place on the planet were like that? Or not? Maybe all places on the planet?

EDIT: I'm not sure if this is more appropriate for fictional science?
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Re: What sort of orbit changes (and other things) would it take for "daylight shifting"?

Postby Soupspoon » Fri Aug 10, 2018 12:50 pm UTC

As time of day is essentially linked to 'local noon' (at least at a representative nominal location for an administrative time-zone, and before part-time daylight-savings offsets are also made) as such, one would have to assume a stick-in-the-mud attitude to the original "astronomical time" clock of yore even when current astronomy (or maybe just helionomy) no longer times things the same.

For constant daylight hours, simply zero your planet's axial tilt. Remove seasonal variations. At least of the kind we currently have.

The alternative would be to wind up/wind-down the spin of the whole pkanet specifically to cause a given off-equatorial latitude to have 'neutral seasons' such as only the tropics sort of experience now. The opposing latitudes will experienced their variations being made more extreme, and the equator start to get the (originally opposing) cycle. And you've probably got other problems with tides and atmosphere sloshing and earthquakes unless you've got an 'inertial vice' over the whole planet. (And it wouldn't work at all for a spot chosen beyond the (ant)arctic circles.)

So with a choice of either 'simple' or !!simple!! to make the day-length constant. Maybe you could use the same mechanisms to make it shift, too, but maybe you've used up that batch of unobtanium-handwavium alloy and need to start afresh with the 'drift'.

Three scenarios come readily to mind, though there are others:
1) Libration. If you just want an extreme "wobble", a constant rotation against the 'stars' but a far more eccentric orbit with faster perihelion and slower aphelion would have the 'effective' solar day advance and recede both ways across 'average' noon for the (presumably) still-24-hoursish¹ cycle. (If you're dynamically adjusting rotation speed to make an extreme-yet-sub-arctic latitude seasonless then the effects combine together, naturally. Somehow.)

2) If you want it to migrate 'around the clock', (6am becomes 5am, becomes… midnight… 6pm… noon… back through 6am) then the spin has changed (less than 24 hours a day-cycle) perhaps why you have nominal 10 hours of daylight (depending upon season and which twilight?) than 12. If there's 20-hour 'real' days but a 24-hour clock is used then you're on a faster spinning planet. Either a faster-spinnng Earth, or an actual other planet that spins faster, but you're using Earth Time for… reasons… (On Mars, you have a slight opposite of the same issue. It spins so that it's a 37ish minutes longer than us to experience a 'Sol' cycle. Earth-based Mars Rover operators tend to switch to Martian time to work the rover shifts, so it begs the question why someone settled elsewhere might not adopt localised timings, though I think 20 hours is an awkward value to adapt down to with circadian rhythms.)

3) Is this 'place' a moving train travelling (near?) constantly around a circumpolar² track? It'd likely work to a geographically-fixed time-zone for ease of confusion, but keep crossing time-zones (eastwards) to get back up to the sun quicker than anyone at 'rest', and pretending to be on a faster-spinnng planet.

....or just redefine the length of hours (20 per Sol, as a sop to a decimalised time of roughly 10 hours each of daylight and night) but forget(/be unable) to reprogram your speed-changed clocks to count 'day ticks' no longer after 24 of your nu-hours?

(Programming errors, and/or going lo-tech and only having sunrise/sunset times to synch variable-speed clocks to and deciding to not even stick to 6am->6pm synching, could explain it all! FCVO 'explain')

¹ Noting that as we're rotating around on our axis (against the 'fixed' stars) and orbiting around the Sun (equivalent to it orbiting around us, once a year) stellar 'days' and solar days are offset by one, and our 24 hours (plus variations requiring of leap-seconds) by solar day are off from the star-fixed days by roughly 1/365.2524ths. For the sake of simplicity, I may ignore that for most purposes. ;)

² This includes equatorial, the biggest circumpolar rhumb of them all. Twice!

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Re: What sort of orbit changes (and other things) would it take for "daylight shifting"?

Postby Xanthir » Fri Aug 10, 2018 10:19 pm UTC

There's no way to do it by just having a planet in orbit. Assuming noon = solar noon, sunrise and sunset are approximately equal distance from noon, by definition. The only way to get them different is to shift the legal definition of "noon" to be not solar noon.

You could fiddle with it *somewhat*, for a relatively limited location, by increasing and decreasing the spin rate during the day/night. For example, if natural sunrise-sunset would be 6am/6pm, you could spin the planet at 2/3-speed from solar midnight until solar noon, so a digital clock would report sunrise at 9am (and solar noon at 6pm), then run it at 2x speed from solar noon to solar midnight, so sunset happens at 9pm (and solar midnight back at 12am, like normal). Elsewhere in the world the divide wouldn't be the same, so sunrise/sunset would happen at different apparent times.
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