What is the proper way to aerate a lawn?

FAQ
Question: 

What is the proper way to aerate a lawn?

Answer: 

Aerate lawns with a core aerator.  Core aerators have hollow metal tubes or tines that remove plugs of soil.  Avoid spike-type devices that simply punch holes (compacting the soil) in the ground.  Core aerators are often available at rental agencies.  Core aeration can also be done by professional lawn care companies. 

Remove soil cores that are approximately three-fourths of inch in diameter and 3 inches long.  For best results, aerate lawns when the soil is moist.  Avoid aeration when soils are dry or wet.  The tubes or tines will not be able to penetrate deeply when the soil is dry.  The tubes or tines may get plugged with soil when the soil is wet.  Lawns that are properly aerated should have 20 to 40 holes per square foot.  Since most aeration machines won’t remove the proper number of holes with a single pass, several passes are often necessary.  After aeration, mow the lawn to break up the soil cores on the soil surface.