Did Cassini get ANY of my Photons?
Posted 19 July 2013 - 05:17 PM
Would any of "my" photons have made it into the image?
Inquiring minds need to know
Posted 19 July 2013 - 06:11 PM
Posted 19 July 2013 - 07:42 PM
Posted 20 July 2013 - 06:48 AM
or say, in more conventional units, if I shine a 1 candle power light how far out do I have to be to be able to "stand between" the photons?
Posted 20 July 2013 - 08:21 AM
Posted 22 July 2013 - 10:04 PM
If we assume they used the Narrow Angle Camera, each pixel covers an angular size of 6 micro-radians. This amounts to 5400 miles for the Earth-Saturn distance. By area, the Earth would cover about 1.7 pixels. Now I'm not sure about the pixel well depth, but if we assume it's at least 100k electrons, then that would mean that of all the photons detected, about 1 in 100000 would have to come from you even after assuming a 100% Q.E. Since you and the Earth are illuminated by the Sun, we can just take the ratio of the areas for the comparison. For an average man standing in the sun, the illuminated surface area (assumed to be half the total surface area) is about 1.0 m^2, but the illuminated surface area for the Earth is about 1.2x10^14 m^2 (the Earth was is in it's 1/4 phase from the point of view of Saturn). The ratio is then 1 in 1.2x10^14 instead of 1 in 100000. So crudely, the odds of them catching your photon is 1 in 1.2x10^9, assuming you were in daylight at the time. Interestingly enough though, this order of magnitude compares well with the population of the Earth (or, of those that are in daylight), so odds are that the camera may have caught a photon from at least one person on Earth.
Do you feel lucky?
Posted 23 July 2013 - 05:53 AM
that is just what I was getting at.
Math is so cool when applied right!
Posted 23 July 2013 - 12:37 PM
2) Please close your blinds next time
III) I can't believe you wore THAT!!
Posted 24 July 2013 - 06:53 AM
Solar flux in the visible is roughly 2.5E20 p/s/m^2 according to one source. Assume a person is 1 m^2 and reflects all arriving photons uniformly into a half-sphere.
The narrow angle camera on cassini is a "2m reflector." If it has a secondary then the collecting area is around 2 m^2. Assume Saturn is about at its orbital distance from earth as it is to the sun - 1.4E12m. (Could be closer or farther).
If all the arriving solar photons are radiated into a hemisphere of radius equal to Saturn's orbit, then 1 photon from a 1m^2 object will enter the camera approximately every 10000 seconds, or 3 hours.
I could have made a mistake but that sounds about right.