Because the Moon's orbit around the Earth is not completely circular, and because the Earth's orbit around the sun is not completely circular, the apparent size of the moon and the Sun vary. The Sun appears largest when the Earth is near it, in January. When the moon is farthest from the Earth, or the Sun is closest to the Earth, the moon won't quite completely cover the Sun. In that case the eclipse is called "annular", because a ring or "annulus" of the Sun is uncovered. That's what we had this past May. Trigger posted a movie of this year's annular eclipse on his facebook page
https://www.facebook.com/Trigger.MMS and on our Youtube channel
http://www.youtube.com/embed/P-L0BSYsgfo
I'll be going to the eclipse in Australia next month... look for Trigger's pictures on his facebook page!