# inequality

In mathematics, an inequality is the statement that
one quantity is less than or greater than another. The symbol > represents
'is greater than', and < stands for 'is less than'.
An example is 2*x* + 4 > 12, which is equivalent to 12 < 2*x* + 4. Inequalities of this type may be handled in a somewhat similar
way to equations; thus, in the case above, *x* > 4.

A **weak inequality** is an inequality that permits the equality
case. For example, *a* is less than or equal to *b*.

In astronomy, an inequality is any irregularity in an object's orbital motion that can't be explained as a result of the mutual gravitational attraction between the body and its primary. Inequalities in a planet's movement around the Sun, for example, are due mainly to perturbations by other planets.

The **great inequality**, also known as **Laplace's
period**, is a slight rocking of both Jupiter and Saturn, as they trek around the ecliptic.
Each oscillation takes some 840 to 960 years (the precise figure isn't
known) and is mostly caused by the near 5:2 resonance of their orbits: Jupiter makes five complete trips around the Sun for
every two (or thereabouts) of Saturn.

The **lunar equality** stems from several factors, which
include the perturbing effects of the Sun and other planets, tidal forces,
and the non-spherical shapes of Earth and the Moon.