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1 vote

Stellar aberration without relative motion between source and observer

There are three sources of abberation: annual (due to the orbit of the Earth) diurnal (due to its rotation) and secular (due to the relative motion of the solar system. The secular aberration is ...
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1 vote

Stellar aberration without relative motion between source and observer

It's impossible to measure instantaneous aberration because there is no reference angle to compare against. What can be measured is the variation of aberration over the course of a year. In 6 months, ...
  • 2,643
0 votes

Why can't we see the far rims of our galaxy by ordinary light?

Mixed in with the interstellar gas (which has almost no effect on visible-wavelength light by itself) are dust grains, which scatter and absorb light. Because the density of gas and dust increases as ...
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5 votes

Crossing of particle horizon and a past light cone

In comoving coordinates, the distance $d_\mathrm{PH}$ to the particle horizon (PH) is equal to the conformal time $\eta$ that has passed since the Big Bang, times the speed of light $c$. That means ...
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