Once upon a time the astronomer equivalent of a shade tree mechanic built a little hut in his back yard, put a bubble roof on it, and installed his home made 12″ diameter telescope in it. Into this private domain he would retreat at unusual and bizarre times of the night, usually in winter when the freezing temperatures gave him moisture-free air and hypothermia. From this he would produce bits of astronomic knowledge and share with other like-minded and warped individuals, and sometimes have a significant impact on the professional community or the world.
Today’s shade tree astronomer has moved from the frigid wastes of the winter backyard to the comfort and coziness of his den, office or next to the fireplace where he can search the records produced by the Sloan Digital Sky Survey at his convenience. From this staggeringly immense repository of information about the cosmos anyone can make discoveries that could shake the foundations of astronomic academia.
And, interestingly enough, one does not need to be a professional astronomer to do so. One simply needs a computer. With this simple device one can tap into the SDSS using the easy-to-use interface and voila, one is chugging happily away with reams and reams on cosmic data!
This article in Universe Today provides more information and links so you, too, can become a shade tree astronomer.