Experiments have shown that the nervous system of the human eye effectively take

Question

Experiments have shown that the nervous system of the human eye effectively takes 30 "frames" per second (like a movie camera) and that when the eye is fully dark-adapted, it needs to receive only about 500 photons per frame from an object to register it. Our sun radiates a power of about 3.9x1026 at all wavelengths, peaking in the yellow region of the spectrum (only about one-half of this energy is in the visible range, however).

Estimate how far away a star like the sun could be and still be visible.

Explanation / Answer

We need 500 photons 30 times a second, this is 15,000 photons each second. we can detect 2 x 10^26 of the photons that the sun puts out every second. Let's say that the dark-adapted pupil has a 3 mm radius. For an area of Pi(.003)^2 m^2 The sun is sending its photon off in all directions the surface area is 4 Pi r^2 m^2 2 x 10^26/15,000 = 4 Pi r^2/Pi .003^2 (2 x 10^26/15,000)*(.003)^2/4 = r^2 r = 173,000 km The sun is a lot further away than this, and I can still make it out, so there is a problem somewhere.

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.