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Astronomy & Science / Re: Tropical Cyclones
« Last post by atomic7732 on November 15, 2020, 09:46:39 PM »Tropical Cyclone Alicia
Recent Posts
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Astronomy & Science / There might be a white hole!
« Last post by 19orb1007 on November 10, 2020, 04:23:59 AM »In general relativity, a white hole is a hypothetical region of spacetime and singularity which cannot be entered from the outside, although energy-matter and light can escape from it. In this sense, it is the reverse of a black hole, which can be entered only from the outside and from which energy-matter and light cannot escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. 
However, some[who?] believe this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed. Although information and evidence regarding white holes remains inconclusive, the 2006 GRB 060614 has been proposed as the first documented observance of a white hole.
Supermassive black holes (SBHs) are theoretically predicted to be at the center of every galaxy and that possibly, a galaxy cannot form without one. Stephen Hawking and others have proposed that these SBHs spawn a supermassive white hole
However, some[who?] believe this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed. Although information and evidence regarding white holes remains inconclusive, the 2006 GRB 060614 has been proposed as the first documented observance of a white hole.Supermassive black holes (SBHs) are theoretically predicted to be at the center of every galaxy and that possibly, a galaxy cannot form without one. Stephen Hawking and others have proposed that these SBHs spawn a supermassive white hole
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Astronomy & Science / Re: Space Engine Runs On Windows Vista-10!
« Last post by planetuniversesandbox on November 08, 2020, 09:51:26 AM »I like these. I edited The Texture And cloud maps
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Astronomy & Science / Space Engine Runs On Windows Vista-10!
« Last post by planetuniversesandbox on November 08, 2020, 09:50:16 AM »WindowSteam
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Astronomy & Science / Re: Tropical Cyclones
« Last post by atomic7732 on October 31, 2020, 01:49:03 PM »obligatory extreme storm post
Typhoon Goni
Typhoon Goni
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Astronomy & Science / Re: Kalassak's Astrophotography
« Last post by vh on October 31, 2020, 09:17:53 AM »oops, i just realized it's probably the lens aperture that matters and not the sensor size (although the ratio of the sensor area to the total area the lens projects the image on needs to be factored in). so ignore everything above until i fix the math. although the units won't change and i still think ujpn is a pretty cool unit
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Astronomy & Science / Re: Kalassak's Astrophotography
« Last post by vh on October 31, 2020, 09:11:46 AM »shimao hijack time
We can measure how much light we've been exposed to in units of steradian meter^2 seconds, where we multiply the time of our exposure (T), by the area of our sensor (A), by the solid angle of sky exposed to the sensor (S). Thus we can compute exposure as STA.
Typically in photography, you might also crop the image, resulting in a ratio of cropped image area to original image area of K. Since the crop affects both sensor area and sky angle by a multiplicative factor, thus we get STAK^2
The solid angle of sky can be related to the focal length (F) and the sensor area with a small angle approximation: S = A/F^2, so we prefer the formula T(AK/F)^2
Example: I made 14 exposures of 15 seconds each with my camera (366.6 mm^2 sensor), a crop ratio of roughly (3/8), and a focal length of 200mm. This comes out to 100 micro sr*m^2*s
If you're confused, here's some intuition: Screen brightness is often measured in nits, where something like 200 nits is a fairly average monitor brightness. It turns out that sr*m^2*s = joule/nit, so if you think of the sky as a really dim and faraway monitor (let's say 0.01 nits), then an exposure of 100 micro joule/nit * (1/100) nits means our sensor was exposed to a microjoule of light energy. If we knew the exact wavelength of light, we could even go further and compute the number of photons per pixel or something like that.
Anyway, since micro sr*m^2*s is annoying to write out, and joule/nit is more intuitive, I propose calling this "ujpn" for "micro joules per nit". This below photograph was taken at an exposure level of 100 ujpn.
We can measure how much light we've been exposed to in units of steradian meter^2 seconds, where we multiply the time of our exposure (T), by the area of our sensor (A), by the solid angle of sky exposed to the sensor (S). Thus we can compute exposure as STA.
Typically in photography, you might also crop the image, resulting in a ratio of cropped image area to original image area of K. Since the crop affects both sensor area and sky angle by a multiplicative factor, thus we get STAK^2
The solid angle of sky can be related to the focal length (F) and the sensor area with a small angle approximation: S = A/F^2, so we prefer the formula T(AK/F)^2
Example: I made 14 exposures of 15 seconds each with my camera (366.6 mm^2 sensor), a crop ratio of roughly (3/8), and a focal length of 200mm. This comes out to 100 micro sr*m^2*s
If you're confused, here's some intuition: Screen brightness is often measured in nits, where something like 200 nits is a fairly average monitor brightness. It turns out that sr*m^2*s = joule/nit, so if you think of the sky as a really dim and faraway monitor (let's say 0.01 nits), then an exposure of 100 micro joule/nit * (1/100) nits means our sensor was exposed to a microjoule of light energy. If we knew the exact wavelength of light, we could even go further and compute the number of photons per pixel or something like that.
Anyway, since micro sr*m^2*s is annoying to write out, and joule/nit is more intuitive, I propose calling this "ujpn" for "micro joules per nit". This below photograph was taken at an exposure level of 100 ujpn.
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Astronomy & Science / Re: Tropical Cyclones
« Last post by Darvince on August 18, 2020, 03:10:24 PM »broken links already
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Astronomy & Science / Re: Tropical Cyclones
« Last post by atomic7732 on August 18, 2020, 04:01:16 AM »Hurricane Genevieve
Tropical Storm Higos
Tropical Storm Higos
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Universe Sandbox 2008 | Help / test
« Last post by Dan Dixon on August 16, 2020, 04:10:03 PM »test