is it necessary to aerate the lawn
A: No. If your lawn is doing fine and the soil isn't compacted, there's no need to aerate at all. (Aeration involves using a machine that removes finger-sized cores from the soil and deposits them on the surface to create more air space.). If your soil is compacted (and many are), fall is a great time to aerate -- ideally right after a rain when the soil is soft. Some years other goals take precedence, though.