How does the declination of the sun vary over one year?

Well, my physical geography teacher said that the sun migrates annually between the tropic of cancer and the tropic of capricorn, which are latitude at 23 and 1/2 degrees N and S. However, I've heard that it varies somewhat in reality--over time so I'm not sure if what she said is absolutely correct or why it varies. The slight variation is because the Earth 'wobbles' about its axis