When the Moon is exactly 270° East of the Sun, it is in the Third Quarter phase.

Here's why:

* Lunar Phases: Lunar phases are caused by the changing angle at which we see the sunlit portion of the Moon as it orbits the Earth.

* 270° East: This position means the Moon is opposite the Sun in the sky, with the Earth in between.

* Third Quarter: At this point, we see exactly half of the Moon illuminated, and that half is the right side (from our perspective in the Northern Hemisphere).

Let me know if you have any other questions about lunar phases!