The phrase "speed of light in a vacuum" emphasizes that light travels at its maximum speed only in a vacuum, where it is unimpeded. In other mediums, light interacts with atoms, causing it to travel slower due to absorption and re-emission processes. The degree of this slowing varies based on the medium's properties and the frequency of interactions. Understanding this distinction is crucial for grasping the behavior of light in different environments. The significance lies in recognizing that the vacuum represents the ultimate speed limit for light.
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Nickriener
10
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OK, I've been wondering, what's the significance of saying "speed of light in a vaccum" if lightspeed is a constant. Is the "vacuum" part even necessary?
Except as a clarification that light only travels in a vacuum...light appears to travel slower through a medium but that is only because of occasional interactions between light and atoms.
Light travels unimpeded in a pure vacuum - where it achieves its maximum velocity. Photons traveling through a medium are absorbed then reemitted by atoms, which slows their journey. The amount of slowing depends on how long the photons are 'held' before reemitted, and the number of captures suffered before reaching an observer.
Partial solar eclipse from Twizel, South Isl., New Zealand ...
almost missed it due to cloud, didnt see max at 0710 NZST as it went back into cloud.
20250922, 0701NZST
Canon 6D II 70-200mm @200mm,
F4, 100th sec, 1600ISO
Makeshift solar filter made out of solar eclipse sunglasses
Is a homemade radio telescope realistic?
There seems to be a confluence of multiple technologies that makes the situation better than when I was a wee lad: software-defined radio (SDR), the easy availability of satellite dishes, surveillance drives, and fast CPUs.
Let's take a step back - it is trivial to see the sun in radio. An old analog TV, a set of "rabbit ears" antenna, and you're good to go. Point the antenna at the sun (i.e. the ears are perpendicular to it) and there is...
This thread is dedicated to the beauty and awesomeness of our Universe. If you feel like it, please share video clips and photos (or nice animations) of space and objects in space in this thread. Your posts, clips and photos may by all means include scientific information; that does not make it less beautiful to me (n.b. the posts must of course comply with the PF guidelines, i.e. regarding science, only mainstream science is allowed, fringe/pseudoscience is not allowed).
n.b. I start this...