Question

At 6300 ˚A (630 nm) the flux from a source is 10−18 W m−2 ˚A−1. Determine the photon rate passing through a telescope aperture with D = 2·2 m over a wavelength interval of 100 A˚ . Calculate the best possible S/N ratio of a measurement with an integration time of 30 s.

Answer 1

Answer on Question #54961, Physics / Astronomy | Astrophysics

Using equation:

$$N _ {T} = \frac {\pi}{4} \times D ^ {2} \Delta t \frac {\lambda}{h c} F _ {\lambda} \Delta \lambda$$

We can calculate the best possible S/N ratio of a measurement:

$$N _ {T} = \frac {3 . 1 4}{4} \times (2. 2) ^ {2} \times 3 0 \times \frac {3 6 0 \times 1 0 ^ {- 9}}{6 . 6 3 \times 1 0 ^ {- 1 4} \times 3 \times 1 0 ^ {8}} \times 1 0 ^ {- 1 8} \times 1 0 0 = 7 4 6 3$$

Answer: $\mathbf{N}_{\mathrm{T}} = 7463$

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