  We show that chirping gravitational waves in the LIGO frequency band $f=1 -
5000$ Hz can be gravitationally diffracted by the Sun, due to the coincidence
of its Fresnel length $r_F \propto \sqrt{1\, {\rm AU}/f}$ and the solar radius
$r_\odot$. This solar diffraction is detectable through its frequency-dependent
amplification of the wave, albeit with low event rates. We also advocate that
solar diffraction allows probing the inner solar profile with the chirping
evolution of frequencies. Along the course, we develop diffractive lensing in
terms of simple convergence and shear of a lens and emphasize the relevance of
high-frequency regimes including merger and ringdown phases for detection. This
work not only presents an interesting opportunity with ongoing and future
LIGO-band missions but also develops the diffractive lensing of long-wavelength
waves in the universe. A similar phenomenon can also help discover
non-relativistic wave dark matter, as studied in a sequel.
