Yes, setting ##\psi(t)=0## without any other changes seems pretty limiting to me. However, I think it might be more reasonable to transform all of the angular variables (i.e., the ##\theta_i##'s and ##\psi##) in such a way that they all start at zero, and such that the sum/average of the...
I think that astronomers in modern times use JD as defined by UT1 (or UTC) (which are, by definition solar days (for UT1 it is not a mean)). However, when doing calculations, a constant day of 86400 SI seconds (in Geocentric Coordinate Time TGC) is more typical (since a uniform timescale is...
The JD defined in terms of UT1 and that defined in terms of 86400 SI seconds only differ (on average) by a few milliseconds. The accumulated difference (which is what ΔT is) builds up, but only over long time periods (70s over the last 100 years as you note from the graph). I will respond in...
The local meridian is the plane of constant longitude passing through ones location (see the Wikipedia article on Meridian (astronomy)). The description he gives is meant to be intuitive (like the picture on that Wikipedia page), not a prescription for measuring your local meridian. To find...
According to Wikipedia, a Julian Day (JD) is measured in Universal Time (UT). The article on UT references an article called Astronomical Time by McCarthy written in 1991 which says that
. Thus, a JD varies with time (presumably daily, assuming the solutions are obtained daily). The article...
According to http://breakthroughinitiatives.org/forum/26?page=1, I was wrong. Dissipating the heat is not considered a big problem.
Also, the website links to two interesting arxiv articles:
A Roadmap to Interstellar Flight - This seems to be the most comprehensive recent analysis to which...
I read up on this a few months ago. I am pretty sure that they had in mind to build the 100 GW worth of laser power as a (phased?) array of ~10,000 10 Megawatt lasers on the ground. The sails themselves would weigh only of order a gram each. It was my understanding that, for the sail sizes...
I think that on the atomic scale this sort of thing can happen. The interaction of light with matter leads to a number of propagating phenomena, for example, optical phonons, excitons, and plasmons. These types of processes involve the movement of atoms and/or electrons in a material and...
A Hamiltonian is the name people give to a "function" (technically a functional or an operator) that takes in the fields or positions and momenta of the things in a system and returns the energy associated with those fields or positions and momenta.
Please give some reference or explanation...
I think it may be a little misleading to say that photon emission causes a change in energy level or vice versa. In order to give the state of the whole system one must say in what state the electron field is and in what state the photon field is. The state is only allowed to change in certain...
The arxiv paper linked here indicates that the maximum amount of data that can be processed is no more than of order 10^120 (another paper linked here indicates that most of this data is encoded in gravitational degrees of freedom). So it seems that in principle there may be ways to store the...
The Earth does produce antineutrinos; they are from the decay of radioactive nuclei (http://www.physicstoday.org/resource/1/phtoad/v64/i9/p14_s1). I am sure the Earth produces neutrinos as well, but I am not aware of a similar measurement for them.
It depends on the method they are using for...
Since the r they use is the relative position vector between the Sun and the planet, the acceleration of this quantity must be the sum of the accelerations of the two bodies (since they both act along this vector to change its length, each attracting the other). So, the force on the planet is...
While what Nugatory wrote is correct, it is unnecessarily complicated. Suppose electric field lines could cross, what would happen if one tried to measure the electric field at the point where they crossed? It makes no sense, because electric field measurements (just like any other measurement...