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Summary: ASTR 3730: Problem Set 1
(due Tuesday September 6th
)
(1) The FERMI space telescope has recently detected flares from the Crab Nebula in
gamma-rays with an energy of around 100 MeV. Suppose that the quiescent flux
from the Crab in photons of this energy is 10-10
erg cm-2
s-1
at Earth.
(a) What is the frequency and wavelength of 100 MeV photons?
(b) If the effective collecting area of FERMI for photons of 100 MeV energy is
103
cm2
, how many photons from the Crab does the telescope collect per day,
on average?
(2) Estimate the theoretical resolution of the human eye, assuming a pupil diameter
of 0.5 cm and a wavelength corresponding to that of green light ( = 0.5 µm).
Express the answer in arcminutes.
(3) A globular cluster has 105
stars distributed within a sphere of characteristic radius
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