  In this work, we measure the volumetric mean radius of the Earth, reproducing
the historical experiment of Eratosthenes, carried out around 240 BC, in the
ancient cities of Siena and Alexandria. Here, we perform measurements in the
cities of Rio de Janeiro-RJ-Brazil and Teresina-PI-Brazil, whose longitude
coordinates are close. Using simple equipment, such as plumb lines and rulers,
we simultaneously measure the height of an object and its shadow's length at
midday, when the Sun is at its highest elevation, in order to obtain the shadow
angle. After determining the distance (latitude) between cities from satellite
data, we use the measured shadow angles to estimate the volume mean radius of
the Earth, from basic trigonometric arguments, finding a result whose error is
$0.5 \% $ with respect to the literature. Furthermore, from the difference of
time in which the Sun is at the highest point in the sky in each location, we
also estimate the Earth's angular velocity. In summary, we pedagogically
present how to obtain the mean curvature of the planet, assuming an
approximately spherical surface, in addition to its angular velocity.
