Publicity often says that a new telescope can detect a candle across the Atlantic, etc.(adsbygoogle = window.adsbygoogle || []).push({});

Well, a candlepower is defined as 1/683 Watts at 540 X 10^9Hz.

This gives photon energy at 2.2 eV.

One candlepower produces 4.2 x 10^15 photons/s radiated isotropically.

At 3,000km the area of the sphere is about 10^14m^2

So the photon density at the telescope is 4.2 x 10^15/10^14 or about 4 photons per sq meter per second.

Two things to note:

The associated electromagnetic field would be very small, but not zero.

A second is a long time in quantum matters.

My questions are: How do you demonstrate the area covered by a photon at the telescope mirror ?

How long is the photon wavetrain ?

(I can’t believe I’m asking this) does the field collapse to the photon particle ?

Is this like the photoelectric effect where a classical calc shows that 10 minutes or so would be required to dislodge the electron, where in fact it occurs in about 10^-9s.

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# Stargazing A new telescope can detect a candle across the Atlantic

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