dotancohen

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bio	website	dotancohen.com
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	age	35
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	1,004 reputation	bio	website	dotancohen.com	visits	member for	1 year, 9 months
213 badges		location			seen	yesterday

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86 Comments

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Apr 15	comment	Other than the motion of the Earth, what else would cause parallax? Right. Thank you!
Apr 15	comment	Other than the motion of the Earth, what else would cause parallax? I see, thanks. Therefore Bradley's discovery of aberration was the final bit of needed evidence?
Apr 15	comment	Other than the motion of the Earth, what else would cause parallax? Thank you for the very informative answer. You do discuss why aberration is easier to detect than parallax, which answers another (unasked) question of mine, but the core question is not addressed: Why was Bradley trying to measure parallax if it had not been discovered yet? And if it had been discovered (or suspected), yet the Earth was supposedly stationary (because Bradley's discovery proved that it wasn't), then what would explain the parallax?
Mar 22	comment	How is celestial navigation done on a low-level? Thank you. The Apollo podcast is very informative.
Dec 12	comment	Blue-shifting as opposed to violet-shifting Thanks, Alan, this is a terrific answer. It doesn't address the question (relativistic blue-shifting), so I won't mark it as accepted, but it is extremely well-written and well-researched. This was fun to read! Thank you!
Dec 11	comment	Blue-shifting as opposed to violet-shifting Nice, thanks! This addresses the red herring, not the question, but it is a very concise way to address the colours of the sky. I wonder why we don't see the sky green, though, as green is no less dominant on the graph and our eyes are very sensitive to green.
Dec 11	comment	Blue-shifting as opposed to violet-shifting @Kitchi: So I guess an ultraviolet source would be shifted away from the blue, yet be erroneously called blueshifted.
Nov 28	comment	How distorted does the Andromeda Galaxy appear to us due to the speed of light? Thanks, Martin.
Oct 24	comment	Maximum resolution per lens size Thanks John! I did realize that a larger lens lets in more light, but I was unaware of spherical aberration.
Oct 24	comment	Maximum resolution per lens size I see, thanks. You've given me the keywords that I do need to continue research. I want to see how far they are pushing this poor lens. However, how is quality reduced as lens size is reduced? All the professional camera have large lenses, surely there is some advantage to a larger lens.
Oct 12	comment	Lowest gravity on Earth's surface? Thank you Dimuthu!
Oct 2	comment	Will a hole cut into a metal disk expand or shrink when the disc is heated? This is analogous to the reason that the holes in cookies get smaller, not larger, when baked.
Oct 2	comment	Gas pressure equalisation: Where does the excess energy go? Thanks John. The microscopic explanation of the gas molecules' speed was quite what I was missing. If Zephyr doesn't write back as an answer then I'll accept this one.
Sep 17	comment	Do any naked-eye stars have planets Thanks. I did know that some doubt had been shed on the existence of the planet.
Aug 17	comment	How empty of fuel are spacecraft booster rockets typically? Thank you. You briefly mention a safety factor of 1.1. Does that mean that roughly 9% of the launch fuel remains?
Jul 31	comment	Does Earth have a code name? I think that the font issues are due to your browser, not the site: ⊕
Jul 24	comment	How did Cook and other astronomers time the 1769 Venus transit? Land-based longitude had its own set of problems, mainly how to transport the clocks (not a problem for Cook). Land navigation was done using Lunar methods even after the seafarers switched to clocks.
Jul 23	comment	How did Cook and other astronomers time the 1769 Venus transit? Actually, longitude was not well-known in the 18th century. I understand that specifically Tahiti's longitude was known, that is why Cook went there. But even measuring high-noon would not be very precise.
Jul 22	comment	How did Cook and other astronomers time the 1769 Venus transit? @dmckee: Thank you for that excellent link! That does suggest that perhaps the lunar distance method was used.
Jul 20	comment	Black hole Cyg X-1 doesn't seem dense enough Thank you, dmckee. I learned Calculus and Differential Expressions in Hebrew, so I did not realise what the "e" in `e^x` really stood for. Wikipedia explains it. Thanks!