odiousgambit
Joined: Nov 9, 2009
• Posts: 8448
January 17th, 2012 at 4:10:15 AM permalink
Quote: Doc

I believe this lack of axis/orbit symmetry is what gives rise to the lack of symmetry in the sunrise/sunset pattern.

I think you are on to something. And I have been reading more.

I was thinking about the whole business as I woke up [was my sub-conscious mind working on this while I was dreaming?] and I have decided that each element must be examined separately. What is happening A#1 is that what I will call the "breadth of the day" is wandering, causing what is called "shifting solar noon". Let's imagine that a day's length does not change. Even so, with elliptical orbits, the time of sunrise and sunset is likely to be changing. I am at the point of imagining a planet on a non-tilting non-elliptical orbit and what happens every complete rotation. The star the planet is orbiting appears to be at one point, then on one complete rotation, why would the star seem to appear at the same spot when the planet has moved along its orbit? [edit:further thought makes me realize this is largely to be expected] We here on Earth expect the Sun to be at that same spot 24 hours later. Why is that? Because the Earth returns to this spot in the nature of its rotation speed! This has to be true! [edit: currently I believe that this must be true if it holds after a great number of rotations and the Earth has moved along on its orbit] This apparently is very common, the study of it has a name: analemma. There must be a reason why a planet in a stable orbit tends to have a rotation that does this.

Our analemma: Because this return to the same spot is not perfect, and because of the effect of the tilted axis, time-lapse photography would show the Sun tracing a figure eight in the sky [over the period of a year I guess]. Astonishingly to me, other planet's do something similar:

from wikipedia, other analemmae:

Mercury: a nearly straight east-west line.
Venus: resulting curve is an ellipse.
Mars: teardrop
Jupiter: ellipse
Saturn: technically a figure 8, but the northern loop is so small that it more closely resembles a teardrop
Uranus: figure 8
Neptune: figure 8
Pluto: figure 8

Unless I am wrong, what I read into this is that if rotational speed was willy nilly, the breadth of the day would wander like crazy. Couldnt there be such planets that don't coordinate rotation speed with a similar daily view of the host star? In a few rotations of said planet, sunrise could easily be changed to what had been the time of midnight, etc, if someone had a clock that was set to time one rotation. It is somewhat miraculous [calling Fr G!], if you ask me, that we can set our clocks to one rotation of the Earth and expect such constancy of sunrise, sunset, etc. We get used to it, and then it becomes a mystery to be solved at winter solstice as to exactly what is going on.

That's where I am with this, anyway. Feel free to tell me I am all wet.
the next time Dame Fortune toys with your heart, your soul and your wallet, raise your glass and praise her thus: “Thanks for nothing, you cold-hearted, evil, damnable, nefarious, low-life, malicious monster from Hell!” She is, after all, stone deaf. ... Arnold Snyder
weaselman
Joined: Jul 11, 2010
• Posts: 2349
January 18th, 2012 at 6:31:52 AM permalink
Quote: odiousgambit

We here on Earth expect the Sun to be at that same spot 24 hours later. Why is that? Because the Earth returns to this spot in the nature of its rotation speed! This has to be true! [edit: currently I believe that this must be true if it holds after a great number of rotations and the Earth has moved along on its orbit] This apparently is very common, the study of it has a name: analemma. There must be a reason why a planet in a stable orbit tends to have a rotation that does this.

It actually does not return to the same spot (thus, the analemma). It would only be the case if the orbit was a perfect circle, and there was no axis tilt (then analemma would be just a single dot). Each of these factors alone results in a fairly simple sinusoidal drift in the daily sun position on the sky, but when they get superimposed on each other, the result is a pretty complicated curve.

Quote: odiousgambit

Couldnt there be such planets that don't coordinate rotation speed with a similar daily view of the host star? In a few rotations of said planet, sunrise could easily be changed to what had been the time of midnight, etc, if someone had a clock that was set to time one rotation.

Indeed. This difference between the "true solar time" and "mean time" (roughly what the clock shows) is called equation of time. On Earth, the largest value for it is only about 16 minutes, but that is because the axis of rotation is not tilted all that much (only about 23 degrees), and the orbit is only slightly elliptical.

Uranus is a notable example of a planet with a very significant axis tilt (it literally can be said to be "lying on its side"), and the time equation on it often reaches several hours. Conceivably, there could be places and times there, where noon happens "at night" (before sunrise or after sunset). I don't know if this is really the case there, but it very well could be.
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FrGamble
Joined: Jun 5, 2011
• Posts: 790
January 18th, 2012 at 2:37:08 PM permalink
I find all of this stuff pretty miraculous!

I hope this doesn't take us too much off on a tangent but we have a parishioner who is working on the James Webb space telescope and he gave a presentation to the parish the other day. It was really interesting. Lots of cool stuff was talked about, including the possibility of seeing back to the beginning of time. However, we spent a lot of time talking about where this telescope will orbit. It will be in a L2 orbit. This was described as being a million miles away from the Earth and on the night side of Earth (away from the sun). It was also shown to not only orbit that far away from Earth but also have what looks like a mini orbital movement of its own. Can anyone shed some light on this type of orbit for me? Also how in the world could a French scientist in the year 1772 have discovered this possibility? Cool stuff.
Doc
Joined: Feb 27, 2010
• Posts: 7071
January 18th, 2012 at 3:29:26 PM permalink
There is a pretty good illustration and discussion of the L2 orbit for this satellite at this web site. I think it is possible for the device just to follow the path of the L2 point around the sun, staying on the dark side of the earth, but there is probably some improvement in stability by letting it "wobble" in a controlled mini-orbit.

As for how Lagrange could have found the solutions to the 3-body problem, well, there were a number of pretty clever mathematicians a few centuries ago -- Newton, Euler, the Bernoullis, Keppler, etc. -- and Lagrange was one of them. Imaging what they could have done with today's tools!
odiousgambit
Joined: Nov 9, 2009
• Posts: 8448
June 24th, 2012 at 12:36:34 AM permalink
If we mine asteroids, I've heard the most valuable mineral will be water, if the rock has some. It's the incredible value of water in space vis a vis on Earth. Didn't we discuss recently that water is where they get oxygen in space?

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the next time Dame Fortune toys with your heart, your soul and your wallet, raise your glass and praise her thus: “Thanks for nothing, you cold-hearted, evil, damnable, nefarious, low-life, malicious monster from Hell!” She is, after all, stone deaf. ... Arnold Snyder
Face
Joined: Dec 27, 2010
• Posts: 4448
January 26th, 2013 at 12:54:54 AM permalink
Back again, and I got another ice problem. It was all fun and games laughing with Ayecarumba a few days ago, but now I'm starting to get nervous...

I have this tank, see. It's about 4' x 2' x 1.5', a tick over 100gal. I usually keep native fish and invertebrates over the summer and release them in fall, but this year I'm attempting a crayfish farm so it's still full. In the fall, the water evaporated to the point the pumps didn't work, and I left it. About 2 weeks ago, it started to freeze.

I immediately added a bunch of hot water to both melt the ice and raise the levels, and it worked fine. The <1" of ice went away and I got the pumps running again. But this last week or so, we got hit with a nasty cold front and even with the pumps running it began to freeze again.

I was laughing with Ayecarumba and posting pics, thinking it was no big deal. At the time, I had about 1.5" of ice that completely covered both sides, both ends, the bottom, and the top; it was just one, big, ice box of water. It was kind of neat to look at, and I wasn't yet scared.

By the time I got done posting about it and browsing DT/WoV, the ice was 2". By the time I woke up 8 hours later, it was 4". When I woke up this morning, the pumps were struggling. By this evening, the pumps were froze solid and ceased operation.

My question is - How does ice work? It has been my thinking that as the ice forms, it'll displace liquid water due to it's larger volume. As long as I keep some part of the surface open, the displaced water has somewhere to go and the tank pressure will not rise. My fear is that I got it all wrong, and I'm about to lose a lot of time, hundreds of dollars of equipment, and suffer a not-insignificant amount of water damage to my garage.

I got one pump running again and have a 6" open hole in the ice. None of the glass looks bowed nor do the seams seem to be pulling apart, but I imagine something like this will look completely fine right up until the point it explodes.

I'd much appreciate some direction. I'm kind of thinking I'm good, but it's too expensive a mistake to not ask. If you're rusty on your chemistry, then feel free to just take bets on whether my garage will stay dry until April ;)
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Nareed
Joined: Nov 11, 2009
• Posts: 11413
January 26th, 2013 at 4:55:21 AM permalink
It depends on temperature. Water is odd in that it expands when it freezes, yes, but as the ice gets colder it contracts. Also, if the tank is open, regardless of whether or not it's covered with ice, the opening provides an outlet for pressure.

Remember when soda came in glass bottles? Back then a sealed bottle left inside the freezer had a good chance of blowing up as the contents turned to ice and expanded. But an open bottle wouldn't blow up.
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kenarman
Joined: Nov 22, 2009
• Posts: 966
January 26th, 2013 at 7:33:46 AM permalink
If you pumps and lines are plastic and are able to expand some when they freeze they should survive. If they are metal there is a good chance they will be hooped.

If you can keep any liquid water from becoming trapped under the ice so that it can't expand when freezing then the tank might survive. If you have trapped water that can only expand sideways then it will take the tank out.

I had an outdoor fish tank that I left outdoors every winter and let freeze but it wasn't glass. I always drained it to about 1/4 full at the end of the season.
Be careful when you follow the masses, the M is sometimes silent.
98Clubs
Joined: Jun 3, 2010
• Posts: 1728
January 26th, 2013 at 4:04:49 PM permalink
Ice works by the hydrogen-bonding system. Therefore at 39F water is at its maximum density. Below that temperature, hydrogen bonding becomes relevant and the density of water decreases until frozen. When water freezes into ice, any dissolved gasses (Soda bottles can EXPLODE) either remain trapped in the structure, or are driven out. Ice is especially dangerous in a closed container, as the resulting pressure increase due to the reduced density can bend steel, shatter glass, and ruin an ordinarily sound encasement. Fish tanks are not immune... as the side pressure can also break the glass (remember, you're fighting gravity in pushing that ice UP)
Some people need to reimagine their thinking.
Face
Joined: Dec 27, 2010