DSST Astronomy or Environment and Humanity

[lumpylump]

I took them both and personally found Astronomy easier but only because I have some history with the subject and just needed to brush up on the material based on the guidelines on the official exam fact sheet. Studying for the exam was strictly memorization of facts. I used InstantCert, some freely available material, crammed for about a week, and that was that.

Environment and Humanity wasn't overly difficult despite my lack of background in the subject and since you've already done extensive study for biology you already have a leg up on the material. I used InstantCert, the Environmental Science SparkChart to get an overview, and the Princeton Review title Cracking the AP Environmental Science Exam for more detailed study.

Exam Fact Sheets:
Environment: http://www.getcollegecredit.com/download...manity.pdf
Astronomy: http://www.getcollegecredit.com/download...ronomy.pdf

The fact sheets and sample questions might help you get an idea of what to expect.