1,161 reputation
620
bio website dotancohen.com
location
age 36
visits member for 2 years, 11 months
seen 5 hours ago

Aug
10
awarded  Yearling
Jul
31
comment Does Earth have a code name?
I think that the font issues are due to your browser, not the site: ⊕
Jul
30
revised Will Pluto be in the ecliptic plane when New Horizons passes by? Was this deliberate?
edited title
Jul
24
answered Gas Cylinder Life
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
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
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