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Physics, Astronomy & Cosmology / Re: How many photos are emitted by the sun every second? How many reach earth?

« on: 14/12/2016 10:49:18 »

The figure of interest is not what quantity is reaching the eye looking directly at the Sun but the quantity received when looking at typical objects illuminated by sunlight.
It is recommended that when looking directly at the Sun one should use a density 4 filter giving 40db of attenuation, is reflected Sunlight reduced by that amount ?

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Physics, Astronomy & Cosmology / Re: How many photos are emitted by the sun every second? How many reach earth?

« on: 14/12/2016 00:13:42 »

If we use the 1e45 figure for photons/sec emitted by the Sun, then you get ~1.8e36 photons striking the Earth per sec and 4.4e16 photons per sec hitting the eye (assuming a pupil diameter of 2mm.)

However, the eye figure doesn't take attenuation by the Earth's atmosphere, accounting for that leaves us with ~3.4e16 photons per sec hitting the eye.  This works out to 0.013 watts entering your eye if you are staring directly into the Sun (Not a good idea.)

Using the second, smaller figure would decrease the photon count by a factor of 2000 in each case (but not the wattage)

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Physics, Astronomy & Cosmology / Re: How many photos are emitted by the sun every second? How many reach earth?

« on: 13/12/2016 23:29:20 »

From memory the Sun emits energy with a mass equivalent of 4.26*10^6  tons per second assuming the photons average 2eV the number comes out at approximately 10^45
But I am prepared to have my arithmetic corrected.

The eagle eyed will note I made several corrections my memory of the Suns output and the mass equivalent energy of a 2eV photon were both wrong but at least my arithmetic was OK

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Physics, Astronomy & Cosmology / Re: What would happen to a marble dropped into a hole through the Earth?

« on: 27/07/2016 23:36:40 »

If the Earth was solid, (rather than having a hot soft center), and a hole was drilled all the way through, it would fill with air. The air-friction would slow the marble so it wouldn't overshoot the center by much.  [ Collisions with the tunnel wall would also slow the marble down even further ].

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Physics, Astronomy & Cosmology / Re: What would happen to a marble dropped into a hole through the Earth?

« on: 27/07/2016 23:21:00 »

If there would be no air, the marble would fall and accelerate until it reaches the middle of the earth. Then it would slow down until it would stop on the other side. Then it would fall back to your side in the same manner in a perpetual motion.

In reality, the air would slow it down by friction and the marble would never reach the other side. The oscillation would be shorter for every motion back and forth until it would stop in the middle of the earth where there is no acceleration due to gravity.

I neglected the fact that the earth rotates. The earth rotation would cause the marble to hit the wall in a complexed pattern depending on where you dig the hole... To minimize it, the best would be to dig a hole from the north geographic pole to the south geographic pole.