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# J2 (computed)

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Constant / Last modified by eng on 2017/09/11 02:06
`J_2 = (2 epsilon_E) / 3 - (R_"Earth"^3 * omega_"Earth"^2) / (3G*M_"Earth")`

The `J_2` constant is the Earth's second dynamic form factor used in computing the `J_2` perturbation of the inverse square formulation of the gravitational effect on the force due to a perfect spherical body of uniform density.

**The MATH AND SCIENCE**

This factor can be calculated as:

`J_2 = (2 epsilon_E/3) - (R_E^3 omega_E^2) / (3 G M_E)`

where

- `epsilon_E` is the central body's oblateness (in this case Earth's oblateness)
- `R_E` is the central body's equatorial radius (in this case the Earth's mean equatorial radius)
- `omega_E` is the central body's rotational rate (in this case Earth's rotation rate is `7.292115 X 10^-5` rad/sec
- `G` is the universal gravitational constant
- `M_E` is the mass of the central body (in this case the Earth's mass)

**REFERENCE**

Equation section of Nodal Precession article

**SEE ALSO**

This constant,

**J2 (computed)**, references 5 equations/constants.