How does this union work?

typedef union __declspec(intrin_type) __declspec(align(64)) __m512 {
    float m512_f32[16];
} __m512;

__m512 gravity;
gravity.m512_f32[i]   ?
gravity->m512_f32[i]  ?
gravity::m512_f32[i]  ?

struct PlanetGroup {
    union {
        int   id[VECWIDTH] = {};
        __m256i m_id;
    };
    union {
        float x[VECWIDTH] = {};
        __m256 m_x;
    };
    union {
        float y[VECWIDTH] = {};
        __m256 m_y;
    };
    union {
        float dx[VECWIDTH] = {};
        __m256 m_dx;
    };
    union {
        float dy[VECWIDTH] = {};
        __m256 m_dy;
    };
    union {
        float Fx[VECWIDTH] = {};
        __m256 m_Fx;
    };
    union {
        float Fy[VECWIDTH] = {};
        __m256 m_Fy;
    };
    union {
        float mass[VECWIDTH] = {};
        __m256 m_mass;
    };
    union {
        float r[VECWIDTH] = {};
        __m256 m_r;
    };
};

// I want to just be able to access the __m256 shadows instead of having to declare my own.
// The code is ugly cause of all the shadow declarations