I first thought that the rotation was about the earth's axis, but this doesn't seem to be the case - at least there must be 'added' another rotation. So what rotation is really done ?
I don't know if you saw the starsphere description but it explains a lot about what it all means. In particular the normal viewing point from Earth is located at the center of the sphere. I know that doesn't quite answer your question, but thought I'd point out the link in case you haven't seen it.
While I don't know the official answer to your question, I would bet the rotation axis is actually random. If you are currently crunching a Work Unit, click on the "show graphics" button on the "Tasks" tab in Boinc Manager. Drag your mouse around and you will find you can re-orient the sphere any way you want. When you let go of the mouse, the sphere rotates about whatever is at the "top" and "bottom" of the screen at that time. In other words you can change the rotation axis to anything you want. [extra kudos if you can locate the North Star and orient the starsphere to rotate about it]
I saw it - before reading it I had more question about these graphics ...
Quote:
While I don't know the official answer to your question, I would bet the rotation axis is actually random. (...) Drag your mouse around and you will find you can re-orient the sphere any way you want. When you let go of the mouse, the sphere rotates about whatever is at the "top" and "bottom" of the screen at that time. In other words you can change the rotation axis to anything you want. [extra kudos if you can locate the North Star and orient the starsphere to rotate about it]
smith
I found this possibility to re-orient the sphere, due to reading the above site. And I also observed that the orbits on the screen are horizontal, which means that the axis is that which connects top and bottom of the sphere on the screen.
But is the axis fixed when you don't intervene ? I got the impression that it might be slowly changing, as if for instance precession would be shown (may-be with a shorter period than real - when compared to the 'daily' rotation)
What is / are kudos ? I tried to locate some constellations and the sky poles, but (not being good enough in practical astronomy) I didn't even find Orion - so easy to identify on the real sky when visible - I think I saw one of the Bears (probably the large one) and the W/M-shaped constell. (called Cassiopeia if I'm right). With my (at first) fixed idea that the axis should be earth's rot. axis, I did not find the poles ... although they must then have been near to top / bottom - but not quite, which may also be the reason for my conjecturing that the axis is changing. (I should look at this once more.)
But is the axis fixed when you don't intervene ? I got the impression that it might be slowly changing, as if for instance precession would be shown (may-be with a shorter period than real - when compared to the 'daily' rotation)
Hmm...interesting. I have never noticed that before. Using the mouse cursor to mark the location of a single star, it does not come back to the same place after one revolution. So precession seems to be there, but why it is there and what it means, I don't know.
The screensaver was initially developed by Pirates@Home. I took a quick look their archives but couldn't find anything related to this question. I guess I don't have a good answer to your question. That work pre-dates my time. Maybe someone else knows.
Quote:
What is / are kudos ?
Sorry about that. I was originally going to say that you get extra credit for finding it, but with all the discussions about project credits, I figured it would be best to avoid that word. Anyhow, to quote the Wikipedia entry, "Kudos means fame and renown resulting from an act or achievement; by extension is often used as a praising remark."
As for finding the constellations, I have to admit I am not very good myself. I think I found the big dipper though!
from what Bruce posted i see that code is written in c and using OpenGL
i just did not expect that you would be calculating SINuses
you could simply precalculate the values of sinuses and pick up precalculated values from the table.
Actually the screensaver code is C++. Profiling the code shows that the sin() and cos() calls in this routine do not use significant CPU. So there's no point is using a lookup table.
How do the Einstein@home sky-ball rotate ?
)
I don't know if you saw the starsphere description but it explains a lot about what it all means. In particular the normal viewing point from Earth is located at the center of the sphere. I know that doesn't quite answer your question, but thought I'd point out the link in case you haven't seen it.
While I don't know the official answer to your question, I would bet the rotation axis is actually random. If you are currently crunching a Work Unit, click on the "show graphics" button on the "Tasks" tab in Boinc Manager. Drag your mouse around and you will find you can re-orient the sphere any way you want. When you let go of the mouse, the sphere rotates about whatever is at the "top" and "bottom" of the screen at that time. In other words you can change the rotation axis to anything you want. [extra kudos if you can locate the North Star and orient the starsphere to rotate about it]
smith
RE: I don't know if you saw
)
I saw it - before reading it I had more question about these graphics ...
I found this possibility to re-orient the sphere, due to reading the above site. And I also observed that the orbits on the screen are horizontal, which means that the axis is that which connects top and bottom of the sphere on the screen.
But is the axis fixed when you don't intervene ? I got the impression that it might be slowly changing, as if for instance precession would be shown (may-be with a shorter period than real - when compared to the 'daily' rotation)
What is / are kudos ? I tried to locate some constellations and the sky poles, but (not being good enough in practical astronomy) I didn't even find Orion - so easy to identify on the real sky when visible - I think I saw one of the Bears (probably the large one) and the W/M-shaped constell. (called Cassiopeia if I'm right). With my (at first) fixed idea that the axis should be earth's rot. axis, I did not find the poles ... although they must then have been near to top / bottom - but not quite, which may also be the reason for my conjecturing that the axis is changing. (I should look at this once more.)
RE: But is the axis fixed
)
Hmm...interesting. I have never noticed that before. Using the mouse cursor to mark the location of a single star, it does not come back to the same place after one revolution. So precession seems to be there, but why it is there and what it means, I don't know.
The screensaver was initially developed by Pirates@Home. I took a quick look their archives but couldn't find anything related to this question. I guess I don't have a good answer to your question. That work pre-dates my time. Maybe someone else knows.
Sorry about that. I was originally going to say that you get extra credit for finding it, but with all the discussions about project credits, I figured it would be best to avoid that word. Anyhow, to quote the Wikipedia entry, "Kudos means fame and renown resulting from an act or achievement; by extension is often used as a praising remark."
As for finding the constellations, I have to admit I am not very good myself. I think I found the big dipper though!
smith
From the code: GLfloat
)
From the code:
vp_theta = 90.0 - viewpt_elev + wobble_amp*sin(PI2*t/(wobble_period*60.0));
In words: the viewpoint is wobbled up and down by +- 37 degrees, with a 17-minute period. This is of course in addition to the regular rotation.
Cheers,
Bruce
Director, Einstein@Home
from what Bruce posted i see
)
from what Bruce posted i see that code is written in c and using OpenGL
i just did not expect that you would be calculating SINuses
you could simply precalculate the values of sinuses and pick up precalculated values from the table.
RE: from what Bruce posted
)
Actually the screensaver code is C++. Profiling the code shows that the sin() and cos() calls in this routine do not use significant CPU. So there's no point is using a lookup table.
Cheers,
Bruce
Director, Einstein@Home