Constellations and the Night Sky

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Originally Posted by murf

Would it possible for Hydælyn to have its axial precession occur at such a pace that somehow at least Eorzea remains in relatively seasonally locked location?

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Yeah, if Hydælyn's axis rotated at the exact same rate as its revolution around its sun, (1 revolution per 1 Hydælyn year) then the planet wouldn't experience seasons. It would be much more likely though, i think, that Hydælyn's axial tilt is simply zero degrees. ^^

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Originally Posted by Kenmei

Yeah, if Hydælyn's axis rotated at the exact same rate as its revolution around its sun, (1 revolution per 1 Hydælyn year) then the planet wouldn't experience seasons. It would be much more likely though, i think, that Hydælyn's axial tilt is simply zero degrees. ^^

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Yea, also that. Sometimes I think up convoluted answers before thinking of the simple ones. Damn brain!

Couple things here, just because I think you guys actually want to know the true facts.

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Originally Posted by murf

Would it possible for Hydælyn to have its axial precession occur at such a pace that somehow at least Eorzea remains in relatively seasonally locked location?

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Procession wouldn't be involved here. It changes the direction the pole points, but not how much it's tilted by. So it wouldn't effect seasons. A motion called nutation might have an effect, but is so minor it's not worth considering (on Earth it's only a matter of arcseconds, thousandths of a degree, in size). Procession is what causes the seasons to go out of whack compared to the calendar months and famously why the zodiac is a month off from what newspaper horoscopes claim, but there still would be seasons of the same length as always, just that maybe winter eventually starts in March instead of December if we didn't add leap seconds all the time to counteract it (and don't get me started about the differences between tropical/sidereal/anomalistic/heliacal/Julian/Gregorian/etc years, no one wants to go there...). This is turning into a really long way to say procession won't give us that effect. Moving on!

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Originally Posted by Kenmei

Yeah, if Hydælyn's axis rotated at the exact same rate as its revolution around its sun, (1 revolution per 1 Hydælyn year) then the planet wouldn't experience seasons. It would be much more likely though, i think, that Hydælyn's axial tilt is simply zero degrees. ^^

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Um... Well... that would be a way to get rid of seasons I suppose, technically. But it wouldn't be pleasant and is 100% not what's happening on Eorzea. Such a world would have no apparent rotation of the sky. One half would be perpetual day and the other perpetual night, all year long. The day-side would be a scorching wasteland with the sun always hanging overhead never moving, and the night one a frozen wasteland with no source of heat. Also because this situation is the end result of tidal forces, it either takes a ridiculously long time to happen, or the planet is wayyyy to close to its star to be habitable. Not a pretty place to live, and definitely not Hydælyn.

If it does have an axial tilt though, that gives rise to seasons across the whole planet, you can't really do it selectively for regions. You either have 'em or you don't. But their impact is less noticeable near the equator where instead of spring/summer/fall/winter you get just wet/dry (and also ties in with keeping a constant 12 hour day/nighttime). Which I think is what you're getting at for maybe Eorzea could be locally season-locked. But that would be directly at odds with all our previous evidence showing Eorzea in the northern hemisphere and not on the equator. I'm gonna stick with it's just too bothersome to program and we'll never know unless the devs say otherwise. :P

When able to, I'll try and do some serious Eorzean stargazing to see if I can't give us a good numerical estimate of the latitude, since that should be possible.

Also HELL YEAH Eorzean Astronomical Society!!! I feel motivated to make us a logo now... brb

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Originally Posted by Myranda

Couple things here, just because I think you guys actually want to know the true facts.
... Such a world would have no apparent rotation of the sky. One half would be perpetual day and the other perpetual night, all year long.

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I thought they were referring to the precession having a cycle of 1 year (rather than Earth's 26,000 year cycle), and the planetary rotation still being 1 day (speaking in approximates). So that the planet's north pole is perpetually pointed at the extended northern axis of its sun. The thought of that kind of speed makes me dizzy, but that's a problem I seem to have a lot in this thread. :)

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Originally Posted by murf

Go go Eorzea Astronomical Society!

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Yes!! When's the first meeting? I'll bring pizza.

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Originally Posted by ArkhamNative

Yes!! When's the first meeting? I'll bring pizza.

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The EAS shall meet on roughly once a month on Saturday nights under prime viewing conditions (as near to the new moon as is possible). Bring a blanket, a telescope and an open mind and love for exploration!

Yes, I meant what ArkhamNative described, where the days are normal and the axis itself has a cycle that matches the planet's revolution. Sorry if I wasn't clear there. I realize that having the axis change that quickly is kind of ridiculous but for the sake of argument could eliminate a planet's seasons even if it was tilted. ^^

Looking forward to that EAS logo!

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Originally Posted by Kenmei

Yes, I meant what ArkhamNative described, where the days are normal and the axis itself has a cycle that matches the planet's revolution. Sorry if I wasn't clear there. I realize that having the axis change that quickly is kind of ridiculous but for the sake of argument could eliminate a planet's seasons even if it was tilted. ^^

Looking forward to that EAS logo!

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Well, axial tilts can be strange business. After all Uranus is basically titled damn near 90º and rotates sideways.

I'd like to think it'd be possible to have 0º tilt, but not be tidally locked. On that note, doesn't a tidally locked body technically still rotate (ie: the RL moon)? And wouldn't a planet with no rotation have its 'day' simply last a 'year'?

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Originally Posted by ArkhamNative

I thought they were referring to the precession having a cycle of 1 year (rather than Earth's 26,000 year cycle), and the planetary rotation still being 1 day (speaking in approximates). So that the planet's north pole is perpetually pointed at the extended northern axis of its sun. The thought of that kind of speed makes me dizzy, but that's a problem I seem to have a lot in this thread. :)

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Hmmm... okay I think I see how that's different but it still seems off. This is where it starts hurting even my brain, but I think that may result in the same bad situation where one side ends up getting overcooked and the other side frozen. It wouldn't be perpetual day/night like the tidal locking situation, but you'd still be dumping solar energy more into one hemisphere than the other all the time, creating an imbalance.

Still workin' on the Society logo. :)

[edit to include other replies]

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Originally Posted by murf

Well, axial tilts can be strange business. After all Uranus is basically titled damn near 90º and rotates sideways.

I'd like to think it'd be possible to have 0º tilt, but not be tidally locked. On that note, doesn't a tidally locked body technically still rotate (ie: the RL moon)? And wouldn't a planet with no rotation have its 'day' simply last a 'year'?

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Correct on all counts. A 90° tilt gives rise to extreme seasonal changes, almost as bad as the tidal locking but it at least flipflops over the course of a year.

And Mercury is a good example of almost zero tilt, it's only tilted 2°. It also has a weird 2:3 resonance thing going on with the Sun that isn't quite tidal locking but honestly I don't understand it completely so I'm not sure how to explain it. As weird and interesting as that is, it wouldn't factor in with Hydælyn.

I asked a co-worker (I work for the National Radio Astronomy Observatory) if a planet can have a 0º axial tilt, but still have a standard rotational period that allows for a common day/night cycle. He said it possible, and as expected each day/night would be the same length, and there would be no seasons.

Additionally, back on our longitude issue, he did mention (as I forgot) that Venus is upside is 'upside down' and thus rotates backwards. It would also make its 'magnetic north pole' on its 'geographic south pole.' So the compass may point 'north' but we still may be facing 'south'... but then as I type this I remember that the Eorzean sun still rises in the east and sets in the west so that would mean the rotation is more akin to Earth's. So really... this went no where. Carry on, nothing to see.

My brain is hurting... but full of fun and excitement in this discussion.

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Originally Posted by Myranda

And Mercury is a good example of almost zero tilt, it's only tilted 2°. It also has a weird 2:3 resonance thing going on with the Sun that isn't quite tidal locking but honestly I don't understand it completely so I'm not sure how to explain it. As weird and interesting as that is, it wouldn't factor in with Hydælyn.

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My understanding of Mercury's orbital/rotational ratio is that:

If on the surface of Mercury, the period from one sun-rise to the next (a synodic day) is longer than Mercury's year (how long it takes the planet reach the same position in its orbit).

However, it will actually complete one and half (1.5) rotation within that same year. So after two years, it'll make 3 total rotations and thus be back to where it started.