Square law?
i raise this question because of recently reading some QM, and realizing that for significantly short periods of time, it becomes hard to detect the mathematical patterns. E.g. in the double slit experiment, the standard pattern doesn’t appear after just a few photons. It takes...
OK. I'm sure this is probably been considered before but it is my musings coming off a recent attempt to photograph the Andromeda Galaxy. I did a few two minutes or so shots of Andromeda and stacked them for a total of about 14 minutes. Fairly nice. There is some structure to be seen but...
I understand that Contravariant vectors have an upper index and co-variant vectors use a lower index. But why is one preferred over another in a specific physical situation?
I am just struggling with which form is preferred, and why one would bother trying to raise or lower the index in a...
Yes, I did see ei.ej defined as gij and vice versa. I'll get to the General Relativity subjects shortly enough, and it is fascinating. I just want to understand the basics of how to do the mathematics for right now. So far it's pretty simple basic linear algebra and dot products of equations...
I was seeing ei or ei as a matrix, which my Linear Algebra book does allow for squaring. But regardless, I'm incorrect. I looked ahead in the book, and the examples shown obviously are not the square of the matrix. Or dot product by itself. I just don't see how they get their answer...
In reviewing some basic GR (just to keep my old brain sharp), i was looking at the Einstein notation cinvention and was a bit confused. I see how you do the dot product of say:
ei.ej = δij
(i.e. 1 or 0)
But then the book I'm reading talks about ei.ej or ei.ej. Isn't that just the...
Gliese 581 g, assuming it's real, is supposedly tidally locked being so close to its parent star. That makes sense. It also means it is probably not a very habitable planet - one side being a burnt desert and the other a frozen wasteland, with only the margins capable of supporting life...
Presently we can effectively understand the Universe down to the Plank Time - 10-43 seconds. That's pretty small, but obviously within that time interval a large number of interactions between particles occurred. Before that time we need a better theory of quantum gravity to unify the four...
I always thought I'd do well on that game show: Are you smarter than a 5th Grader? Guess I'd lose - my educational level stops at the fourth.
IAE, my son is lead (i.e. Pb) for his 5th grade science project. He has to tell the class where he came from. I had always thought lead came from one...
Is there anyway to determine a galaxy's distance by figuring out its actual size (or the visual portion) and then reverse triangulate to us? All I hear is about standard candles as the source for determining galactic distances - either Cepheid variables or Supernovae.
We have of course...
I was looking at Jupiter early Sunday morning. Supposedly after the guy in Australia. I can't say I really noticed anything, but wasn't looking for it. I was observing through a 9.25 Celestron with a 14 MM meade lens. It sure looked nice, but maybe I should've been paying better attention -...
Does anyone have a table or formula one can use to calculate the effect of one's elevation above sea level on observing stars? I recall seeing something once upon a time showing how much of an increase in magnitude one gets the higher one goes. But then I recently read that the atmospheric...
I realize that Starlight atmospheric absorption depends on frequency, but I was wondering if there are any tables indicated total bolometric absorption at Zenith relative to absorption at Sea Level. Obviously atmospheric absorption is much less on the top of Everest than in my hometown (a few...
http://www.nature.com/news/2006/060320/full/060320-11.html
I see from the above link that we have found a new solar twin, HD 98618. It is 126 light years away. Too far away for meaningful communication (unless we are willing to wait 250 years for an answer), but close enough that we could...
Some great answers so far indeed. But I think that many of them just beg the question. Why would a globular cluster evolve in such a way to begin with? What happened to the metals from the original stars that were big enough to go supernova? And why are there only such smaller stars in them...