The Lunar Eclipse is red because the light of the sun is shining through the edges of the Shadow Object which passes between the sun and moon during a Lunar Eclipse. The red tint occurs because the outer layers of the Shadow Object are not sufficiently dense. The Sun's light is powerful enough to shine through the outer layers of the Shadow Object, just as a flashlight is powerful enough to shine through your hand when you put it right up against your palm.
The globular earth is said have a circumference of 24,900 miles while the atmosphere is said to extend only 100 miles around it. If the RE model were true, and the redness of the shadow was caused by the sun's light filtering through the earths atmosphere, then the earth's shadow upon the moon would only have a slight sliver of red around the shadow's edges. The moon could not turn entirely red as it does in the above image. The fact that the moon turns entirely red during a Lunar Eclipse suggests that the light of the sun is flowing through the majority of the body which intersects the path of light. Clearly an impossibility in the RE explanation.