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Sun-path and Sky Dome cross-sections through the year


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Here's a couple of diagrams I threw together to illustrate the movements of the Sunpath and the Sky Dome.

 First, an East-West vertical cross-section through Glorantha. The thick black line is the Surface World; the circle is the Sunpath; where they cross are the Gates of Dusk (W) and Dawn (E). The Sunpath never varies to north or south, but in Winter Yelm is lower in the sky, dimmer and cooler. In Genertela he appears to be "going south"; but at the same time, in Pamaltela (the southern continent), he appears to be "going north". In Summer, of course, Yelm is higher in the sky, brighter and hotter, and appears to be more directly overhead. 

Yelm's Wheel.png

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Second, a North-South cross-section [UPDATED BELOW] showing the movements of the Sky Dome. It is perfectly centred at Midsummer, then skews northwards through Autumn until Midwinter, rocking back to the central position through Spring until Midsummer.

One interesting nuance: in Winter, celestial fire drips from the southern edge of the Sky Dome onto the Southern Continent, affecting the climate in Pamaltela. (There is no comparable effect in the North)

Sun Dome Tilt.png

Edited by Nick Brooke
Use the corrected diagram later on in this thread.
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Oh, I'll just stress that these are not to scale, are probably exaggerated, and YGWV. They're based on assumptions made when I was working on the Gloranthan Ephemeris for Greg in the nineties: I started by literally implementing what was described in Elder Secrets, and that's when we found that things went weird if the Sky Dome's movements were symmetrical: if you have stars showing up low in the northern sky in winter, they'll also show up low in the southern sky in summer: that's how symmetry works.

One alternative model would have Polaris as a fixed point about which the Sky Dome wobbles to and fro, I think we discarded that because the idea of the Perfect Sky only existing one night of the year (Midsummer Night, when the axis is vertical and the Dome is centred again) had such a strong appeal. Also because those wobbles were hard to imagine (for us, I'm sure you are much cleverer). YGWV.

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Lightfore moves quickly across the summer sky in those short (8 hours?) nights, while he idles along the Sunpath at midwinter, taking twice that time. Diametrically opposed to what Yelm does.

 

This north/south rhythm isn't quite what I expected. You've made the point about rotational symmetry before.

 

I worked under the assumption that the winter sky would tilt to the south, spilling some celestial fire into the seas there, before returning to the upright position. Why would the heat spill result from tilting northward? Do you regard the sky dome as an isolating layer between the Inner World and the fiery sky above?

Kalikos (the midnight jumper) rises the highest above the horizon in winter - I had assumed that this was following the celestial tilt, not running against it. As a Jumper, this star is fixed in its cardinal position, so rotational symmetry doesn't come into this.

One Night Wish (which peeks above the southern horizon on Midsummer) apparently defies any classification. A hypothetical local jumper would be the noon jumper, invisible to everybody but the Yuthuppan Star Seers (and for them, possibly obscured by mountain chains).

Likewise, One Night Wish only peeks above the southern horizon on midsummer.

In your model there should be an entire catalogue of "underworld stars" visible in the midwinter southern sky. Probably for the entire edge region since the night is so long. But if the firespill happens then, shouldn't that affect the appearance of the southern sky?

 

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The Sky Dome also rotates clockwise, one complete rotation every year. (Thus producing a sidereal year, along with the tropical year defined by the interval between summer solstices, which can be easily defined as the night when Lightfore occludes Polaris at midnight, and just possibly a lunar year definable by the cycles of the Red and Blue Moons... but the definition of the Blue Moon's cycle in the Guide is plainly inaccurate, since a literal reading would mean that Gloranthan tides only occur around the vernal equinox. In any case, as far as we know, all of these years are identical in length, or close enough to not be noticed.)

Each hour, therefore (assuming that it's a smooth, analog rotation and not a digital one), the stars which move with the Sky Dome change their position by 3.1 arcminutes, or about 1/10th of the apparent size of the Sun. This is certainly visible with the naked eye, but a subtle effect. How, then, does this affect the Jumpers? 

Kalikos has an "orbital" period of between 8 and 16 hours. Rausa has an "orbital" period of between 4 and 8 hours. Theya has an irregular "orbital" period between 4 and 5 hours. Assuming that they move straight up into the sky and then back down in a literal sense, then the Sky Dome will rotate between 25 and 50 minutes of arc under Kalikos, between 12 and 25 minutes of arc under Rausa, and between 12 and 16 minutes of arc under Theya. Or, in other words, the greatest degree of shift nightly is 0.2% of the total angular distance of the Sky. As such, it's probably not really determinable whether these stars truly go straight up and down, or have a highly elliptical orbit in the sky which brings them back down to the same point they rose from. 

You could probably classify the two fixed constellations as very slow Jumpers, with an orbital period of 294 days each. 

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2 hours ago, Joerg said:

Lightfore moves quickly across the summer sky in those short (8 hours?) nights, while he idles along the Sunpath at midwinter, taking twice that time. Diametrically opposed to what Yelm does.

Since Lightfore is Yelmalio, it is unsurprising to find him methodically and meticulously patrolling the night sky in Dark and Storm seasons, smiting trolls. Not "idling" at all. Marching with purpose.

2 hours ago, Joerg said:

I worked under the assumption that the winter sky would tilt to the south, spilling some celestial fire into the seas there, before returning to the upright position. Why would the heat spill result from tilting northward? Do you regard the sky dome as an isolating layer between the Inner World and the fiery sky above?

You know, on reflection I think I may have got this backward. Now I think about it, Greg's vision of how the Perfect Sky broke was that the Unholy Trio lifted up the edge of the Sky Dome in the North when they let Chaos back into Glorantha from outside; so it springs off axis then, and the wobbly axis varies from upward to south-leaning. And, as you say, when the Sky Dome dips south, celestial fire spills down to replenish the Sea of Flame south of the Nargan Desert. Solution: swap the N & S labels, and eat a small portion of humble pie.

Jumpers are weird and a bit silly, and I tend to ignore them.

Jeff and I agree that the firespill on the southern horizon makes things strange down there. In the northern sky, I've always thought the Ice Palace is more likely to be something aurora-like rather than a strange constellation only visible in winter. But what do I know?

At this distance in time and enthusiasm, I can't remember what I put into the Ephemeris. I stopped working on that when we were finalising Moonson in earnest. 

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1 hour ago, Nick Brooke said:

At this distance in time and enthusiasm, I can't remember what I put into the Ephemeris. I stopped working on that when we were finalising Moonson in earnest. 

Personally, I found it very useful, particularly during rituals and omen-reading.  Thankfully, you included the Boat Planet so that part works fine post-Dragonrise.  

2 hours ago, David Scott said:

I've just checked that this venerable Java app still works - and it does, get it here. (your experience may vary...)

I used to be able to get it to work reasonably with certain browsers.  Unfortunately, Chrome is not one of them as it doesn't like to run Java code.

What browser are you using to run it?  Or are you running within some other Java development environment?

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10 minutes ago, jajagappa said:

I used to be able to get it to work reasonably with certain browsers.  Unfortunately, Chrome is not one of them as it doesn't like to run Java code.

What browser are you using to run it?  Or are you running within some other Java development environment?

Using Windows, Chrome is fine using IE Tab extension AND authorizing https://wellofdaliath.chaosium.com/site-apps/ephemeris/EphemerisII.html url in Java security tab in "Configure Java" control panel.

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2 hours ago, jajagappa said:

What browser are you using to run it?

No browser - as a Java App. 

2 hours ago, jajagappa said:

Or are you running within some other Java development environment?

https://www.java.com/en/ direct from oracle,  Click here to download the zipped Ephemeris java app, unzip and run the EphemerisII.class file (on a Mac running Big Sur).

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What I find really interesting about this is it suggests that in southern Pamaltela we get TWO hot seasons - one in Fire Season, another in Dark Season and Storm Season. Which might be why the Sikkanos Winds are so awful - instead of the rain-bringing Orlanth storms (which Umathela gets), the Pamaltelan plains get blasted by hot dry winds coming off the Nargan. It also means that the plains are dependent on the Keraun Winds bringing WARM rains in Earth, Dark, and Storm Season.  These rains are warm as they are coming right off the Togaro. Wongarrasi has got to be just awful, making the Wastelands look nice.

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On axial tilt, here's a relevant quote from the Guide to Glorantha: it's the caption to one of Eric Vanel's awesome Copper Tablets, vol.1 p.117:

Quote

"Fatally wounded by Shargash, Umath crashed upon North Camp. This started the tilting north-south Dome Movement. It went northward first, because the Pillar there was broken, until it was pushed back even harder by Kalikos. The rebellious Sons of Umath then rose out of the ruined North Camp, bearing the weapons of their dead father."

My interpretation: (a) the initial northward movement is "pushed back even harder," so it could still settle as a centred-to-south-leaning annual tilt; (b) this happens before the Unholy Trio let Chaos into the world (insofar as sequencing matters in Godtime, Umath crashed in the Golden Age), so another push from the North comes later.

tl/dr: Not inconsistent with my Sky Dome diagrams above, but I thought it'd be worth sharing.

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Second quote, from Appendix A: The Sky (Guide to Glorantha, vol.2 p.644):

Quote

Annual Tilt of the Sky Dome
The Sky Dome tilts back and forth, north and south, each year. It tilts upon two unmovable hinges, the Gates of Theya and Rausa, which have remained unbroken since the world was first created. These gates do not move around, but are immobile. From Theya’s Gate the Sun and many of the Planets depart for their journeys across the sky at their respective times. They set, later, at Rausa’s Gate.
In summer, it tilts north, exposing stars in the south which are invisible in the winter and sending the Sun’s path to the north of the center of the sky.
In winter, the dome rocks back, exposing northern stars and concealing the southern and making the Sun’s path cross the sky south of the center. The dome dips slightly further to the south than it does (later) to the north. The God Learners believed that the sky spilled out fire during its winter tilt, warming the southlands, and making the Ocean of Fire there.

OK, under this sustained pressure from subsequent sources I'll scrap my "Perfect Sky on Midsummer Night only" element from the scheme. There's two nights, somewhere in between the equinoxes and the summer solstice, when the Sky Dome is (briefly) perfectly centred again, but they're quickly over and nobody seems to mark the occasions. (Perhaps this is something the Pole Star cult would get excited about, I dunno?)

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Kinda in speculation here but my interpretation of the Unholy Trio letting chaos into Glorantha, the unholy trio is not Thed, Ragnaglar and Malia as gods but the plants creating a conjunction that dangerously destabilises the Sky Dome "once every six hundred years".  In Pelorian sources those plants are the Blue Moon, Wagon and Black Dendara.

This conjection happened with some regularity in the Storm Age leading to frequent musterings against Chaos until one pretty bad defeat at Storm fall.  That also explains why there is a confusion about when Vingkot was killed.  The world does not seem Chaotic in th aftermath of his death as opposed to Stormfall where eveything turns to hell.

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I wasn't aware of that third push by the Unholy Trio, so my previous assumption was that the annual tilt was a bit to the north (following the crash of the northern Pillar) and then a heavier push backwards to the south, until the sky relieves itself of some of its heat and tilts back. One consequence of that could have been a slower return from the extreme southern tilt towards the north, and of course there would be two days of restoring the position of Polaris on the Sunpath, rather than the one in the model above.

Would the lack of the northward tilt cause a problem with the alternative Kalikos myth in Entekosiad (the one with ice accumulating on the Sky Dome, not the one with Kalikos reacting to Umath's crash by stepping in for the crushed pillar)?

On the southern end of the lozenge, the sky spill marks the end of the Artmali Empire, and/or the urban civilization of Tishamto that had successfully rebeled against at least one incarnation of the Artmali Empire. Given a naval presence of the Artmali north of Fonrit, it appears that there was an Artmali Empire post-Breaking of the World. But then, Pamalt's fight against Vovisibor appears to be pre-Breaking of the World, too. Little wonder the God Learners were unable to make sense of Pamaltela as a whole. It may be impossible to impose a clear "temporal" (as in linear Time) sequence of these Godtime events, but then that's the nature of cyclical Time. It's a similar conundrum to why there is a winter sun at all (Yelm never saw winter, except from Hell), how there is an ascending arc for Yelm on the Sunpath, only the descending half of which was defined by Yelm, Or how the Brown Elves got established - some myths associate the slaying of Yelm with the aldryami going to sleep. Simultnnity probably doesn't matter much.

Edited by Joerg
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On 12/1/2020 at 6:58 AM, Nick Brooke said:

There's two nights, somewhere in between the equinoxes and the summer solstice, when the Sky Dome is (briefly) perfectly centred again, but they're quickly over and nobody seems to mark the occasions. (Perhaps this is something the Pole Star cult would get excited about, I dunno?)

Yo, Yuthuppa, get on this, stat! You need to do a holiday around this. Sacrifice a cheese or something, I don't know, I'm not yer dad!

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