dotancohen

1,004 reputation

213

bio	website	dotancohen.com
	location
	age	35
visits	member for	1 year, 9 months
	seen	May 9 at 8:32
stats	profile views	57

	1,004 reputation	bio	website	dotancohen.com	visits	member for	1 year, 9 months
213 badges		location			seen	May 9 at 8:32

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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 22	asked	How did Cook and other astronomers time the 1769 Venus transit?
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!
Jul 19	accepted	Might a planet perform figure-8 orbits around two stars?
Jul 19	answered	Might a planet perform figure-8 orbits around two stars?
Jul 19	comment	Impact location that created the moon +1 on the coffee analogy. Tomorrow morning I will ask my daughter that question regarding my own cup of coffee!
Jul 19	comment	Black hole Cyg X-1 doesn't seem dense enough Thank you, I had a feeling that I was using the wrong units for G and you understood exactly why! As for quadratically / exponentially, wouldn't "dropping off quadratically" be `1/x^4` whereas "dropping off exponentially" would be `1/x^2`?
Jul 19	comment	Black hole Cyg X-1 doesn't seem dense enough I seem to have a problem with the units. The initial formula gives `(m/s)^6 / ( (m/s^2)^3 * g^2 )` which reduces to `m^3 / g^2`. What am I doing wrong? According to my finding, density cannot decrease exponentially with mass.
Jul 19	comment	Black hole Cyg X-1 doesn't seem dense enough Thank you, I did not realise how rapidly the density goes down with mass. A bit later I'll sit on that for a 1 million solar mass object, just to see what values of "reasonable" are! Thanks!
Jul 18	comment	Black hole Cyg X-1 doesn't seem dense enough Thank you! I see it now mentions in the article that the radius of the event horizon is 26 km.
Jul 18	accepted	Black hole Cyg X-1 doesn't seem dense enough
Jul 18	asked	Black hole Cyg X-1 doesn't seem dense enough
Jul 13	accepted	Will Pluto be in the ecliptic plane when New Horizons passes by? Was this deliberate?
Jul 13	comment	Will Pluto be in the ecliptic plane when New Horizons passes by? Was this deliberate? @dmckee: I refer to the amount of energy required to move a device from 1 AU distance from the Sun to 40 AU distance from the Sun (due to the increase in gravity potential from the Sun). That energy requirement would go down as Delta-V goes down, but equipping the craft with more Delva-V capacity would be the method by which more energy is invested in getting to that distance (in the form of rocket fuel).
Jul 12	accepted	Pressure loss after water goes up and back down 7 stories
Jul 12	accepted	Cannon on spacecraft: hitting yourself
Jul 12	asked	Will Pluto be in the ecliptic plane when New Horizons passes by? Was this deliberate?
Jul 9	comment	Cannon on spacecraft: hitting yourself Right, the speed hasn't changed but the velocity vector has.
Jul 9	comment	Pressure loss after water goes up and back down 7 stories Thank you. There would not be a heating pump installed. I also feel that 16mm is very thin, but that is the standard. In fact, most homes run that thin plastic pipe all the way from the heating tank to the home with no insulation! At my last place I insulated the pipe myself.