Proof: Universe not expanding faster
in [Relativity]
|
Prev: The Pillars of Black Holes are Shaking
Next: THE QUEST FOR THE ULTIMATE THEORY OF TIME, AN INTRODUCTION TO IRREVERSIBILITY
From: Sam Wormley on 23 May 2010 11:45 On 5/23/10 10:27 AM, guskz(a)hotmail.com wrote: > #2. If space was to expand at the rate of half a light-year, what > would be the intensity of the star at one light years distance? Your sentence makes no sense. A light year is a unit of distance. Expansion of space is most often given in the form of velocity per unit distance. For example, H_o = 72 km/s/Mpc This Hubble constant states that the expansion velocity is 72 km/s at a distance of 1 Mpc. The apparent magnitude of a star is a function of its absolute magnitude and its distance. For background on the inverse-square law, see: http://en.wikipedia.org/wiki/Inverse-square_law
From: Sam Wormley on 23 May 2010 11:59 On 5/23/10 10:45 AM, Sam Wormley wrote: > On 5/23/10 10:27 AM, guskz(a)hotmail.com wrote: >> #2. If space was to expand at the rate of half a light-year, what >> would be the intensity of the star at one light years distance? > > Your sentence makes no sense. A light year is a unit of distance. > Expansion of space is most often given in the form of velocity per > unit distance. For example, > > H_o = 72 km/s/Mpc > > This Hubble constant states that the expansion velocity is 72 km/s > at a distance of 1 Mpc. > > The apparent magnitude of a star is a function of its absolute > magnitude and its distance. > > For background on the inverse-square law, see: > http://en.wikipedia.org/wiki/Inverse-square_law > If you are not familiar with the relationship between apparent and absolute magnitude, see: http://scienceworld.wolfram.com/astronomy/ApparentMagnitude.html
From: Sam Wormley on 23 May 2010 12:19 On 5/23/10 10:27 AM, guskz(a)hotmail.com wrote: > #1. Is the intensity of a laser inversely proportional to the distance > from the source? Answer is no. Why no? Because laser is not a point source is does not obey the inverse square law in the near field. Lasers do obey the inverse square law at very large distances. For more background, see: http://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/inversesquare.html
From: bert on 23 May 2010 14:48 On May 23, 12:19 pm, Sam Wormley <sworml...(a)gmail.com> wrote: > On 5/23/10 10:27 AM, gu...(a)hotmail.com wrote: > > > #1. Is the intensity of a laser inversely proportional to the distance > > from the source? Answer is no. Why no? > > Because laser is not a point source is does not obey the > inverse square law in the near field. Lasers do obey the > inverse square law at very large distances. > > For more background, see: > http://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/inversesquare.html Bad thinking for lasers do obey the inverse square law. Best to keep in mind their source is of great power. Its power weakens still with distance the same as a 90w bulb is only 30w at 3 feet TreBert
From: Sam Wormley on 23 May 2010 15:04
On 5/23/10 1:48 PM, bert wrote: > > Bad thinking for lasers do obey the inverse square law. Best to keep > in mind their source is of great power. Its power weakens still with > distance the same as a 90w bulb is only 30w at 3 feet TreBert The SI unit for luminance is candela per square meter. If the luminosity of your bulb is 90 cd/m^2 at a distance of 1 ft, then the luminosity of your bulb is 10 cd/m^2 at a distance of 3 ft. |