Joseph Smith's 1820 vision

The LDS faith (Mormons) believe Joseph Smith had a vision in 1820 where he saw 2 beings in a pillar of light decending from above. He believes they were God the Father and Jesus and that they spoke to him. What actually was this encounter? Linda Moulton Howe mentioned she thought it may have been extra-terrestrial in nature.

Curious if EA has ever looked into it. I've been LDS all my life and am now waking up to all things cosmic.