void Density(double d) noexcept { density = d; size = std::cbrt(mass / density); }
double Density() const noexcept { return density; }
double Size() const noexcept;
double Age() const noexcept;
void Density(double d) noexcept { density = d; size = std::cbrt(mass / density); }
double Density() const noexcept { return density; }
double Size() const noexcept;
double Age() const noexcept;