He is both as he controls the Earth right now. Earth is in void.
Once Luffy sits on it he will shine on Earth.
Once Teach sits on it he will bring darkness to Earth.
Imu should be named Terra or Gaia if he represents Earth.
Teach represents the Moon. He will become the Moon God once he kills Garling and steals his DF. I think Garling won the Moon God DF at God Valley, but he only has the unawakened version because his mind and body aren’t in sync. Teach will awaken the fruit and become Moon God. Either that or Oda retcons the Yami into a secret Mythical Zoan like he did with the Gomu.
Oda is Shanks’s #1 wanker, so I honestly wouldn’t be surprised if his real name was Figarland Earth or something like that (don’t see how Roger would know what was the real name of the baby he found in the chest, so Shanks was probably a name given to him by Roger)