Recent content by DarkEternal

you can derive the chandrasekhar mass limit with a back-of-the-envelope argument that i think was first presented by landau. basically, you note that the total energy in the star is roughly the sum of the fermi energies of the baryons and the gravitational binding energy; the star is unstable...

Here is a picture of a sunset with a jet contrail that I took atop Las Campanas Observatory, in Chile. http://web.mit.edu/deternal/Public/Chile/LCO1PF.jpg

i prefer shankar; his treatment is reasonably mathematical and very clear.

i've heard good things about artin and mattuck, and i took modern algebra with kac, who was great. however, I've heard not-so-great things about lustzig... but congrats!

http://mcraefamily.com/MathHelp/GeometryTrigEquiv.htm (see Machin's formula)

yes...by gauss's law, the field inside such a distribution increases linearly with distance from the center; thus, the point at which the field is equal to the external field and opposite in direction will be an equilibrium point for the positive charge.

i believe this problem is discussed in griffiths's E&M book, chapter 4. you need to know the field at a distance from the center inside a spherical charge distribution, and find the point where that field counterbalances the external field. the displacements are small, so you can assume the...

I will second the loss of the X-ray spectrometer. I was actually interning at GSFC this summer under one of the instrument scientists involved with the project, and was there when the failure occurred. He was extremely disappointed, especially since the calibration results came back looking so...

Hi all, I'm taking an optical astronomy lab this semester. Does anyone have any recommendations for interesting objects to observe in the optical range with 11"-14" telescopes? I will probably get 3-5 hours of observing time, and of course the object has to be visible in the fall. The...

hmm...i think maybe YOU had better go try it, james jackson. i just did, and as far as i can tell, it just confirmed what i originally thought: the 45 degree polarizer has to go BETWEEN the other two for light to transmit.

nice one calc...go ahead!

nice tries, but no. there's no trick answer...

you have 10 pennies on a desk, 5 heads up and 5 tails up. the room is dark so you cannot distinguish between them. split the pennies into 2 groups, each with the same number of heads up. you are allowed to flip the pennies, but you can't cheat by feeling them.

heartache and headache?

no, an orthogonal matrix's transpose is the inverse of the matrix, so A^{-1}=A^T.