In the Rose Garden / The Astronomy/Cosmology/Astrophysics Lovu Lovu Thread

Giovanna · Back to Top

Well I can make it harder with an explanation people used to use to explain extra dimensions. Imagine a sphere. Imagine there is a dot inside the sphere, and let's say it starts at dead center, and the dot is the sphere's radius from any surface of it. The dot moves. It is still the sphere's radius from any surface. To put it another way, in the kind of space this inside of the universal balloon is considered to consist of, you can be anywhere in it and the exact same distance you were before you moved from anything else. Nothing is there on such a scale that you can't even call it empty space. Because of this, normal rules of location don't apply, because there's no way to target a center any more accurately than pointing at the whole thing.

A little further and you hit the other brick wall. Remember Einstein's whole thing about motion and time? Kinda requires a concept of location that's rather familiar to us. Point A to point B, but here, point A and point B are the same place and just gah nevermind that noise! There's no concept of time in this 'area' of space. So you can't point to it and say 'this is older than this'.

In practice, as I've understood it, this concept of the balloon and having an inside (by property of the metaphor) is more of a mathematic guideline than part of most models of the universe. It's required for certain basic calculations, and predicts accurately within its realm, but there isn't actually any such space there, or not there, as my description would suggest. There is expansion, and for us to reasonably calculate that and imagine it borderless, this application is necessary. But possibly not the reality. Kinda like NASA using classic Newtonian physics to decide flight plans and entry points and such for the shuttle. Newtonian physics accurately predicts the behavior of objects of the sizes involved, though it absolutely falls apart under close analysis at a smaller scale. (Short and dirty: On the small scale, gravity is the absolute weakest force.)

Stormcrow · Back to Top

Damn, this makes me want to draw some Poincare discs...

Giovanna · Back to Top

Explain if you're gonna use scary math terms in this thread! emot-mad (Cuz I'd like to know!)

Honestly my knowledge of the math rarely even touches the terminology. I understand astrophysics in terms of explanations of the physical properties, usually using clever metaphors like balloons and mobius strips. I can wrap my mind around pretty crazy concepts, but I know nothing of the math that drives them.

Nanami's Rose Groom · Back to Top

Another concept popped into my mind. Might sound strange, and if it's not possible, just correct me. I gave provided the link to the "Sounds of space" - radio waves sent by space objects, that were converted to become audio files in a hearable spectrum. We know the location of a few planets...I think two or three, which are lying in their parent star's habitable zone. The radio waves of Earth, unlike of other objects were really soothing, and calm (due to oxygen/nitrogen atmosphere? living creatures? radiowaves sent into space?). SETI...umm...now it's Project Origins, analyzes only the radiowaves in a specific spectrum. I wonder is it theoretically possible to catch the radio waves from the planets that lie outside our solar system, and convert them in the same way, as radio waves of other objects. Maybe there would be a significant pattern or trace of some kind of biological activity... emot-confused

Stormcrow · Back to Top

The Poincare disc is one of the models of hyperbolic geometry. You draw a circle. That's the entire universe (we're talking about a plane here, only two dimensions). Now, if you draw a diameter of the circle, that's a line. The ENTIRE line, in all it's infinite length. On the other hand, a line that we would normally think of as straight is not actually a line in this model unless it's a diameter of the circle. If you want other lines, that don't pass through the center, they are actually formed by constructing another circle, such that the tangent lines to the circles at the points where they intersect are at right angles. You can just think of the circles being at right angles to each other. So the arc of the other circle that passes through the original circle (the universe) is also a line.

This sounds kind of complicated, I know, but the advantage of this model is that it's "conformal", which means that if the lines intersect, they do so at the apparent angle in the model, and you can measure it directly. The Beltrami-Klein model does not have this feature. Distances on the other hand, are obviously not preserved. The way that works is that apparent distances closer to the center are actually shorter than the same apparent distances toward the rim.

Overall, I don't think a Poincare disc would work for what you're describing, but I always think of them when I think of alternate geometries.

Giovanna · Back to Top

I need to meditate on this Poincare business. I approve, and yes, it definitely inspires the line of thought I'm coming from. Also seems to be a good place to start wrapping one's mind around Branes.

In the meantime, since this came up in the IFD thread about what SKU characters would do when encountering their own hentai:

Katzenklavier wrote:
Akio - Get bored and watch a meteorite penetrate a distant planet instead, then wildly stroke himself fantasizing about the insignificance of existence and the inherent nihilism of the meaningless universe.

In 1994, the comet Shoemaker-Levy-9 collided with Jupiter. I almost crapped a brick when I saw the date because it felt to me like something that'd only happened six or seven years ago. But this collision was the first time man has ever directly witnessed the collision of two heavenly bodies. Penetrate is also an apt word to use here, since Jupiter, being a gas planet, had no ground to crash into. The comet simply penetrated the gas clouds and brought havok upon the already storming planet. The collisions (as the comet broke apart in the planet's upper atmosphere) created swirling disruptions in the visible surface of the planet that were incredibly prominent, even viewable from decent home telescopes. Completely cool shit, and I remember watching the NASA folks watching this and my god you've never seen so many delighted fanatical nerds at once.* emot-biggrin CARNAGE PICS:

(Pics from NASA's JPL page on the whole affair.)

Doesn't look like much in pretty Hubble pics, but keep in mind that the largest impact, fragment G, was equivalent to 600 times the world's whole nuclear arsenal. school-eng101 (Thanks Wiki!)

*There was no masturbation at NASA HQ. Probably for the better because while I love nerdy NASA space geeks, most are not quite as attractive a mental image as Akio stroking himself while amused at the meaningless of the world and lack of reason to do anything more in contribution but satisfy oneself.

Nilamarthiel · Back to Top

So, uh, I need a bit of help.

Mostly, I get Declination. In fact, I get it almost completely. I'm having a bit of a block when it comes to Right Ascension. In my notes it says that it is "like longitude", BUT not the projection of Earth's longitude -- it projects into space. And it is measured in time. This is what trips me up on my Overthinking-O-Meter. It's measured on a Sidereal Clock, which makes me go, "...what?"

I tried to make a diagram to express my problem.

Here we've got Boötes. Fuck yeah, Boötes! And I just put a random time in there for the R.A.

And then we have an hour later. As we can see, the constellation has moved 15◦ in the past hour. Now. I changed the 22h to 23h. Am I correct in doing this? Because something seems a bit off on this.

Also, Sidereal Time has to come from a specific place on the Earth. Or does it, for some reason, only apply to where you are located at the time?

I really hope I'm making sense with my question. If someone can explain it to me better than the book, that'd be great. ;o;

Giovanna · Back to Top

Let's see if I can hit all the points there. Had to google to remember some of the terminology, lol. emot-smile

Right Ascension is equivalent to longitude in that it's a vertical across the plane in the same direction as earth's. It looks and smells the same, so you're right on that. It's not a projection of earth's longitude in that earth's longitude uses the Prime Meridian as the zero. This was an arbitrary spot in England we chose to represent zero longitude. Greenwich standard time is the time at which the vernal equinox occurs at the prime meridian. RA doesn't span its numbers out from this point, it uses a point in space as its Prime Meridian, called the First Point of Aries. (The position of the sun during the vernal equinox, so considerably less arbitrary.)

And yes, it's measured in units of time. This is retarded and confusing, but it's one of those ROFLS WELCOME TO ASTRONOMY things. A circle has 360 degrees, yes? An hour of ascension is equal to 1/24 of this, just like hours in day. 1/24 of 360 is 15 degrees of arc. From there it's divided into 15s, which is to say you have 15 degrees of arc = 1 hr, 1 minute of right ascension = 15 minutes of arc, and 1 second of right ascension is 15 seconds of arc. This is done because figure 24 hours is required to move a single star across the 360 degrees of sky during a rotation of earth. If a star/constellation moved 15 degrees, it means an hour passed. So you're correct in that you've added an hour.

Right ascension is a number that goes up as you go eastward from the meridian. Sidereal hour angle is the same thing but it goes up westward. I don't think it uses the hour system, but don't quote me on that. I'm not sure what exactly you're asking about sidereal time. Sidereal time is time based on earth's position in the larger celestial sphere. Solar time is based on its position relative to the sun. The earth has a very slight, well, wobble that isn't significant in a solar day, but it makes the solar day slightly different from time passing measured in sidereal time. So Sidereal time comes from space, and that points at a spot on earth that we measure. Earth's longitude is the other way around, it's decided by a spot on earth and moves out. (The aforementioned wobble is why this can't be used for prediction of location of celestial bodies.)

Edit: Love the bug eyes emot-rofl