CraigD Posted April 15, 2013 Report Share Posted April 15, 2013 Hi Craig. I have to disagree, the speed of light is not a dimensionless number.I believe you misread my post. I wrote (emphasis added)No speed is a "pure" (also called unitless or dimensionless) number.The speed of light is a speed (which has dimension L/T), so is not dimensionless. How light sources that have different speeds can only give a single spectralshift?As JMJones has been explaining, with references to wikipedia, it’s well known to astronomers that they don’t I suppose you think that a particular spectralshift corresponds to a uniform motion of the star at some specific speed.But the star is not a light source, just like as a swarm of bees is not a signle bee.Star has a huge set of light sources that have very large and different relative velocities in different directions. (like our Sun)Galet, I believe your confusion arises from assuming that the speeds of the atoms in a star are “very large”, and that any speed due to temperature makes measuring the redshift of the star difficult. The speed of the molecules in a gas are given by their Maxwell–Boltzmann distribution, which is a function of its mass and temperature. It’s a good exercise to calculate the most probable speed for a specific gas and temperature, such as molecular hydrogen and the Sun’s photosphere’s temperature. You should find a value of about 9800 m/s, which gives a small red/blue shift of about z=0.00003. This is very small compared to the differences in the frequencies of the characteristic spectral lines that allow the composition, rotational speed, and speed of stars relative to the observatory to be calculated. More important, on average, their velocities are the same as the surface of the star - the "average out". The best way to understand these ideas, I think, are to actually calculate the emitted and observed frequencies for many cases for individual atoms in the star. Though time consuming, the math and physics concepts involved are not overly complicated. If you do the work and post it, the good folk here at hypography will help you by checking it and helping with mistakes and difficulties. Eclogite and JMJones0424 2 Quote Link to comment Share on other sites More sharing options...
Dane Posted April 16, 2013 Report Share Posted April 16, 2013 OK. I understand. Thank you! Quote Link to comment Share on other sites More sharing options...
Dane Posted October 29, 2016 Report Share Posted October 29, 2016 A few hours ago I sent a message, but now it's gone. Please tell me why it's deleted. Quote Link to comment Share on other sites More sharing options...
CraigD Posted October 30, 2016 Report Share Posted October 30, 2016 A few hours ago I sent a message, but now it's gone. Please tell me why it's deleted.Your post isn’t deleted, but moved to its own thread, here, because it is not about this topic, the speed of light, but rather appears to be a claim about trisecting an angle. Quote Link to comment Share on other sites More sharing options...
333 Posted November 19, 2016 Report Share Posted November 19, 2016 Light, EM wave, gravity and electrostatic force all have the same speed, there must be serious connection. 2 electrons at r distance exists a force f=kee/rr, that force is the carrier of EM radiation. That's why light speed is equal to electrostatic force speed and decay at distance square. Atoms are constantly vibrate, share their vibration EM force with other atoms, f=gm1m2/rr and f=kq1q2/rr connected all matters. The whole universe is ruled by the two forces. Quote Link to comment Share on other sites More sharing options...
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