A total lunar eclipse occurs when the moon is completely submerged in Earth’s dark, inner shadow, called the umbra. If the moon is only partly covered by the umbra, or only enters the outer shadow (called the penumbra), it is considered a partial lunar eclipse. The total eclipse is said to “begin” when the moon is fully covered by the umbra; this phase is also called “totality.”
The following are the stages of the super blue blood moon:
1. Moon enters Earth’s penumbra: The shadow cone of the Earth has two parts: a dark, inner umbra, surrounding by a lighter penumbra. The penumbra is the pale outer portion of Earth’s shadow. Although the eclipse begins officially when the moon enters the penumbra, this is, in essence, an academic event. You won’t see anything unusual happening to the moon just yet. The Earth’s penumbral shadow is so faint that it remains invisible until the moon is deeply immersed in it.
2. Penumbral shadow begins to appear: Now the moon has progressed far enough into the penumbra that the shadow should be evident on the moon’s disk. Start looking for a very subtle, light shading to appear on the moon’s left portion. This will become increasingly evident as the minutes pass, with the shading appearing to spread and deepen. Just before the moon begins to enter Earth’s dark umbral shadow, the penumbra should appear as an obvious smudge or tarnishing of the moon’s left portion.
3. Moon enters Earth’s umbra: The moon now begins to cross into the Earth’s dark central shadow, called the umbra. A small dark scallop begins to appear on the moon’s left-hand (eastern) limb, or it’s apparent edge. The partial phases of the eclipse begin; the pace quickens and the change is dramatic. The umbra is much darker than the penumbra and fairly sharp-edged. As the minutes pass, the dark shadow appears to slowly creep across the moon’s face. At first the moon’s limb may seem to vanish inside of the umbra, but much later, as it moves in deeper you’ll probably notice it glowing dimly orange, red or brown. Notice also that the edge of the Earth’s shadow projected on the moon is curved. Here is visible evidence that the Earth is a sphere, as deduced by Aristotle from lunar eclipses he observed in the fourth century B.C. Almost as if a dimmer switch was slowly being turned down, the surrounding landscape and deep shadows of a brilliant moonlit night begin to fade away.
4. 75 percent coverage: With three-quarters of the moon’s disk now eclipsed by the umbra, the part of it that is immersed in shadow should begin to very faintly light up— like a piece of iron heated to the point where it just begins to glow. It now becomes obvious that the umbral shadow does not create complete darkness on the lunar surface. Using binoculars or a telescope, the shadow’s outer part is usually light enough to reveal lunar maria and craters, but the central part is much darker, and sometimes no surface features are recognizable. Colors in the umbra vary greatly from one eclipse to the next, reds and grays usually predominate, but sometimes browns, blues and other tints are encountered.
5. Less than 5 minutes to totality: Several minutes before (and after) totality, the contrast between the remaining pale-yellow sliver of the moon’s surface and the ruddy-brown coloration spread over the rest of the disk may produce a beautiful phenomenon known to some as the “Japanese Lantern Effect.”
6. Total eclipse begins: When the last of the moon enters the umbra, the total eclipse begins. How the moon will appear during totality is not known. Sometimes the fully eclipsed moon is such a dark gray-black that it nearly vanishes from view. But it can also glow a bright orange. The reason the moon can be seen at all when totally eclipsed is that sunlight is scattered and refracted around the edge of Earth by our atmosphere. To an astronaut standing on the moon during totality, the sun would be hidden behind a dark Earth outlined by a brilliant red ring consisting of all the world’s sunrises and sunsets. The brightness of this ring around Earth depends on global weather conditions and the amount of dust suspended in the air. A clear atmosphere on Earth means a bright lunar eclipse. If a major volcanic eruption has injected particles into the stratosphere during the previous couple of years, the eclipse is very dark.
7. Middle of totality: The moon is now shining anywhere from 10,000 to 100,000 times fainter than it was just a couple of hours ago. Since the moon is moving to the south of the center of Earth’s umbra, the gradation of color and brightness across the moon’s disk should be such that its upper portion should appear darkest, with hues of deep copper or chocolate brown. Meanwhile, its lower portion — that part of the moon closest to the outer edge of the umbra — should appear brightest, with hues of reds, oranges and even perhaps a soft bluish-white.
8. Total eclipse ends: The emergence of the moon from the umbral shadow begins. The first small segment of the moon begins to reappear, followed again for the next several minutes by the Japanese Lantern Effect.
9. 75 percent coverage: Any vestiges of coloration within the umbra should be disappearing now. From here on, as the dark shadow methodically creeps off the moon’s disk, it should appear black and featureless.
10. Moon leaves umbra: The dark central shadow clears the moon’s right-hand (western) limb.
11. Penumbra shadow fades away: As the last, faint shading vanishes off the moon’s right portion, the visual signs of the eclipse come to an end.
12. Moon leaves penumbra: The eclipse “officially” ends, as it is completely free of the penumbral shadow.
