 
Summary: ASTR 3730: Problem Set 1
(due Tuesday September 6th
)
(1) The FERMI space telescope has recently detected flares from the Crab Nebula in
gammarays with an energy of around 100 MeV. Suppose that the quiescent flux
from the Crab in photons of this energy is 1010
erg cm2
s1
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
