A galaxy with an apparent magnitude in the V band (λc ~ 5550 angstroms, width δλ ~ 800 angstroms) of mV = 22.5 mag is observed with the Palomar 200-inch telescope. How many photons per second are collected from this galaxy over the 200-inch (~ 500 cm) diameter mirror? (assume for simplicity that the filter throughput is = 1 within that bandpass, and that galaxy's photon spectum is flat, and ignore any absorpton or inefficiencies). Answers within roughly 60 photons of the correct answer will be accepted; this question is worth two points.
3 answers
1.3378e19
150 photons
150
1 answer