  We have measured the spherically averaged bispectrum of the SDSS DR17 main
galaxy sample, considering a volume-limited $[273\, \rm Mpc]^3$ data cube with
mean galaxy number density $1.76 \times 10^{-3} \, {\rm Mpc}^{-3}$ and median
redshift $0.093$. Our analysis considers $\sim 1.37 \times 10^{8}$ triangles,
for which we have measured the binned bispectrum and analyzed its dependence on
the size and shape of the triangle. It spans wavenumbers
$k_1=(0.082-0.472)\,{\rm Mpc}^{-1}$ for equilateral triangles, and a smaller
range of $k_1$ (the largest side) for triangles of other shapes. For all
shapes, we find that the measured bispectrum is well modelled by a power law
$A\big(k_1/1 Mpc^{-1}\big)^{n}$, where the best-fit values of $A$ and $n$ vary
with the shape. The parameter $A$ is the minimum for equilateral triangles and
increases as the shape is deformed to linear triangles where the two largest
sides are nearly aligned, reaching its maximum value for squeezed triangles.
The values of $n$ are all negative, $|n|$ is minimum $(3.31 \pm 0.17)$ for
squeezed triangles, and $4.12 \pm 0.16$ for equilateral. We have also analyzed
mock galaxy samples constructed from $\Lambda$CDM N-body simulations by
applying a simple Eulerian bias prescription where the galaxies reside in
regions where the smoothed density field exceeds a threshold. We find that the
bispectrum from the mock samples with bias $b_1=1.2$ is in good agreement with
the SDSS results.
