  We describe the BOOMERanG experiment and its main result, i.e. the
measurement of the large scale curvature of the Universe. BOOMERanG is a
balloon-borne microwave telescope with sensitive cryogenic detectors. BOOMERanG
has measured the angular distribution of the Cosmic Microwave Background on
$\sim 3%$ of the sky, with a resolution of $\sim 10$ arcmin and a sensitivity
of $\sim 20 \mu K$ per pixel. The resulting image is dominated by hot and cold
spots with rms fluctuations $\sim 80 \mu K$ and typical size of $\sim 1^o$. The
detailed angular power spectrum of the image features three peaks and two dips
at $\ell = (213^{+10}_{-13}), (541^{+20}_{-32}), (845^{+12}_{-25})$ and $\ell =
(416^{+22}_{-12}), (750^{+20}_{-750})$, respectively. Such very characteristic
spectrum can be explained assuming that the detected structures are the result
of acoustic oscillations in the primeval plasma. In this framework, the
measured pattern constrains the density parameter $\Omega$ to be $0.85 < \Omega
< 1.1$ (95% confidence interval). Other cosmological parameters, like the
spectral index of initial density fluctuations, the density parameter for
baryons, dark matter and dark energy, are detected or constrained by the
BOOMERanG measurements and by other recent CMB anisotropy experiments. When
combined with other cosmological observations, these results depict a new,
consistent, cosmological scenario.
