Well there are many ways to do this; if you are
in a space craft, the angular separation of the
limbs of the planet can be used to get the radius
when the distance between the observer in the
spacecraft and the planet are known.
Another way is to use a” planetary
transit”. This means that, if a planet crosses
the face of its parent star and this event can be
observed, then the SLIGHT decrease in luminosity
of the star that is being occulted can be
translated into an estimate of the radius.
The radius and the mass of a planet are very
important in order to calculate the density of
that planet. The mass of the planet can be
calculated using spacecraft tracking; then, the
ratio of mass to radius cubed is the DENSITY.
Density is the most critical variable to know in
order to understand the evolution and nature of
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