Jᴀᴄᴜʀᴜᴛᴜ - Tʜᴇ Cᴀsᴛ Oᴜᴛ

But the sky shouldn't look "black". Darker maybe.

Evidently the atmosphere behaves just like the oceans and the crust: the rotational spin of the planet flattens (thins) it at the pole and bunches it at the equator. The thinner the air, the less scattering of the sun's rays and the darker the sky appears overall. But if you're seeing a black sky, you should be having trouble breathing, too.

I found a Google Book with the following height ranges for the various levels of the atmosphere (low for polar regions, high for equatorial):

Troposphere, 5 - 8 miles
Stratosphere, 8 - 30 miles
Mesosphere, 30 - 50 miles
Ionosphere, 50 - 340 miles
Exosphere, 340 - 620 miles

http://books.google.com/books?id=sPCgsy ... t&resnum=5" onclick="window.open(this.href);return false;

No way to say what the values might be for Arrakis, of course.

SandChigger wrote:But the sky shouldn't look "black". Darker maybe.

Evidently the atmosphere behaves just like the oceans and the crust: the rotational spin of the planet flattens (thins) it at the pole and bunches it at the equator. The thinner the air, the less scattering of the sun's rays and the darker the sky appears overall. But if you're seeing a black sky, you should be having trouble breathing, too.

I found a Google Book with the following height ranges for the various levels of the atmosphere (low for polar regions, high for equatorial):

Troposphere, 5 - 8 miles
Stratosphere, 8 - 30 miles
Mesosphere, 30 - 50 miles
Ionosphere, 50 - 340 miles
Exosphere, 340 - 620 miles

http://books.google.com/books?id=sPCgsy ... t&resnum=5" onclick="window.open(this.href);return false;

No way to say what the values might be for Arrakis, of course.

Is this why it's easier t see the aurora borealis (and it becomes more wildly coloured of course) as one goes further north? Less atmosphere to look through?

No, actually I think that's caused by cosmic rays and the solar wind getting caught in the excessive muff hair originating in Red Deer and recently reported to be spreading across the Canadian polar regions.

Good Gawd ... that must mean there's someone just like HER in the southern hemisphere as well.

(Seriously, it's because the lines of force of the Earth's magnetic field fold into the north and south poles and the charged particles follow them. Or something like that. There's nothing similar going on at the equator, being blocked from view by the thicker atmosphere. )

SandChigger wrote:(Seriously, it's because the lines of force of the Earth's magnetic field fold into the north and south poles and the charged particles follow them. Or something like that. There's nothing similar going on at the equator, being blocked from view by the thicker atmosphere. )

I'm having a bad week, I already knew (or should have) that it was because of the feilds. I obviously need to switch to higher powered coffee.

SandChigger wrote:(Seriously, it's because the lines of force of the Earth's magnetic field fold into the north and south poles and the charged particles follow them. Or something like that. There's nothing similar going on at the equator, being blocked from view by the thicker atmosphere. )

That last part is not true. All the charged particles from the sun are directed to the poles.
Watch this short clip.
and this clip.

I wasn't saying that the atmosphere is thinner or thicker at different lattitudes. Rather, the light from the sun hits Earth at shallower angle in the polar lattitudes which means it has to pass through more of it.

Same concept as sloped armor.

http://en.wikipedia.org/wiki/File:Slope ... ram_v7.png" onclick="window.open(this.href);return false;

SandChigger, could you check in your Arrakis-model in Celestia what a 1 or 2 degrees axial tilt would do to the day/night cycle in Arrakeen and Carthag?

Ahp. I've been looking for my simple surface texture with the locations marked. Guess I'll have to make a new one.

Another quote from Messiah. Scytale visits a house in Arrakeen:

It was the proper hour, though. The pale sun stood almost directly overhead. People
of this quarter remained sealed in their houses to sleep through the hot part of
the day.

The sun directly overhead at that latitude? Not possible.

Obviously he didn't think through all the details.

Do we know anything about axial tilt? Probably can't rule it out unless we do.

I thought I posted something about that.

I know I fiddled with the Celestia stuff after posting that up there in July. Maybe I forgot to post the results?

You did put something up. Just reread it and was wondering if the relative size of Arrakis' sun (Canopus?) compared to Sol would make any difference?

Hmm ... good question. How large Canopus appears in the sky depends on how far Arrakis is from it. But I don't think you'd want to be close enough that the apparent size made it look like it was overhead when it shouldn't...

I threw together this little thing, just eyeballing the positions.... The size of the planet doesn't matter for this, AFAIK.



The blue line is the axis of rotation, tilted relative to the plane of orbit around Canopus (long horizontal orange line). This is the extreme case, with a tilt of 30 degrees. The red line indicates the latitude of Arrakeen (again, probably higher north than this according to the Dune map). As Arrakis turns around its axis, Arrakeen will (appear to) travel back and forth along the segment of the red line within the circumference of the planet (outline of the circle), from the PoV of the diagram. The short orange lines (from the center of the planet intersecting the circumference at Arrakeen latitude and extending beyond) indicate the direct of directly overhead at noon. (I think ... probably on the solstices only?) The true location of the sun (Canopus) would be along the long orange line.

As you can see, Canopus would come closest to appearing directly overhead in high summer ... but it would still be about 30 degrees off.

What's more important though is the effect this degree of tilt has on the amount of sunlight received at Arrakeen: in the summer there is almost no darkness, and in the summer only a few hours of light. When you consider that the actual map latitude is probably higher than in my mock-up, you should be able to see that anything more than a few degrees of axial tilt would make Arrakeen uninhabitable.

Or rather, bizarre enough a setting that the details should be reflected in/have an influence on the narrative.

I'll look up my latitude figures for Arrakeen and try to work up a more accurate diagram, for different tilts and rotational durations.

Continuing a bit...

By comparison, the Earth currently has an axial tilt of 23.44 degrees, according to WP.

The longitude & latitude values I currently have in my Celestia files for Arrakeen are 27.79 W 62.29 N. (The Arctic Circle is at 66.56 N, remember.) I used Google maps to put this into perspective:



So if Arrakeen were on Earth, it would be in the North Atlantic, to the southwest of Iceland, as shown by the balloon marker labelled A. (The other balloon is the location over land with the longitude reversed, 27.79 E. No significance, was just playing.)

I re-read the thread and noticed this quote in my first post:

Frank Herbert in GEOD wrote:With First Moon almost directly overhead, it was quite light in the forest and, although these were the higher latitudes of Arrakis it was still warm from the heat of a summer day

The first moon is directly overhead at higher latitudes... That means the moon is in a polar orbit. In our solar system there are no moons in polar orbits.

Hm... could it be Frank Herbert's 'directly overhead' is not what we think he means? Maybe something like 'directly in front of him in the sky' ?

Thanks for the map, SandChigger. The middle part of Finland then.

According to this site:
Daylight in Finland through the year

In winter, the middle part of Finland has 5 to 6 hours between sunrise and sunset. However, I wonder how much of the 'night' is really dark?
Now, is it possible Arrakis has an axial tilt similar to the Earth, say 20 degrees...?

EDIT: I found this on a blog:

In November, December, and early January, Helsinki has as little as 6 hours of daylight. But, we don’t have high noon sunlight. The sun hovers above the horizon, like it is 10:00 in the morning all day. Then, around 3:15pm, the sun dips below the horizon and night falls until 9:15am, when the sun barely makes its way above the horizon again.

and

In contrast, June and July bring eighteen hours of daylight. Night never really comes. The sun rises at 3:30am and sets around 11:30pm. Nighttime is a soft, steel blue dusk.

Just thought i'd throw my two pennies(cents if your from Us or the Euro zone).

Seasons do not necessarly equate to a axile tilt. If Arrakis orbit where eliptic they would have a global summer (where it was closest to the sun) and a global winter where it was furthest away.

You're right about that.
But Arrakis must have an axial tilt because the fremen used a horizon calendar.

SandChigger wrote:

I can't tell you how impressed I was by this "thrown together" diagram, but ...

... was the shadowing around the black square *really* necessary?

HBJ

Hunchback Jack wrote:

SandChigger wrote:

I can't tell you how impressed I was by this "thrown together" diagram, but ...

... was the shadowing around the black square *really* necessary?

HBJ

He's a professional.

Actually, it's the default and I forgot to turn it off. I zapped it on the circles because it looked wrong. Like I said, thrown together.

(Used The Omni Group's OmniGraffle, for any other Mac users who might be innerested. )

SandChigger wrote:Ahp. I've been looking for my simple surface texture with the locations marked. Guess I'll have to make a new one.

just downloaded Celestia(I grew up with a dad who grew up with Star Trek and the 1st man on the moon so anything that lets me go boldly is cool)
thanks for the link

btw does your quote mean you can create a new "celestial body" in that simulation?

Still trying to figure out our diagram (might use that for a demotivator )

lotek wrote:btw does your quote mean you can create a new "celestial body" in that simulation?

Yep.

I assume the set-up is the same on Windows ... inside the application folder there should be a folder named Celestia Resources (or similar). Inside THAT there's a folder named Extras.

Inside that folder on my machines I have a folder named "duniverse". It currently contains six items:

duniverse.ssc = file that contains planet & satellite data (puts Arrakis around Canopus, etc.)
duniverse.stc = file for adding stars not currently included by Celestia
locs.ssc = file for labelling locations (like cities [Arrakeen on Arrakis] or geographical features ["The Palmeries"], etc.)
models (folder), currently empty (would contain 3D models for irregularly shaped asteroids, spacecraft, space stations, etc.)
(test.ssc = files I use for quick tests of stuff, currently empty)
textures (folder), contains another folder called "medres" containing various texture images, like surface maps for planets, surface textures for 3D models (like a solar collector image for solar panels on satellites, etc).

A lot of stuff, but not really all that complicated...