The Moon spends 25% of its orbit within the terrestrial magnetosphere. The magnetic field from the terrestrial magnetosphere can potentially provide radiation shielding from solar energetic particle events and lower energy galactic cosmic rays, which can be a significant hazard during extra-vehicle activities or during human exploration of the lunar surface. The level of shielding provided by the terrestrial magnetosphere is calculated in conjunction with 3D multi-fluid simulations of the terrestrial magnetospheres. It is shown that the level of shielding is dependent on IMF orientation and location of the lunar base. The natural terrain could be used to augment the terrestrial shielding for an equatorial lunar base. A polar lunar base would be exposed to twice as much radiation. But in both cases shielding of GeV particles is possible, with the upper range depending on the prevailing solar wind conditions.