Totality Begins

Totality begins when the Moon is fully within Earth’s umbra. The Moon looks reddish because Earth’s atmosphere filters and bends some sunlight around the planet. As sunlight passes through Earth’s atmosphere, shorter wavelengths (such as blue) are scattered in every direction, so the blue light does not reach the Moon. The longer wavelengths of light—red, orange, and yellow—are not scattered as much, so they continue traveling through the atmosphere and on to the Moon. 

There is a gradation of color because the central portion of Earth’s shadow is darker than the edge. The reddish color is visible now because the whole Moon is dim.