Mist or fog?

If you were up bright and early this morning, you will know that it was an unusual morning :)

Today was the first warm morning of the season, and the air contained a lot of moisture.

On my way to work, I was thinking, "Hmm, is this called fog or is it mist?" In my first lesson, my student also asked the same question. We checked the dictionary, and maybe this morning's weather should be called fog. The main reason is that it was quite thick and visibility was poor. Usually I can easily see the Mitsui Building but as you can see in the second photo, the central buildings are not visible at all!

By about 8:30am, the sun was higher and all the fog was burned off. Now it is sunny :)