The forecast for Saturday morning: Mostly clear and chilly with a dimming moon!
The earth, moon and sun will be aligned in the pre-dawn hours Saturday, resulting in a total lunar eclipse.
Southern Arizona won't be able to see it enter and exit the eclipse phase, because it will happen as the moon is setting. However, the first phase, from full moon to entry into totality will be visible to Tucsonans.
For best results, watch the eclipse from a location without large mountains to the west. Since the moon will be putting on the show fairly low in the western sky as it sets Saturday morning, large mountains to the viewer's west could impede much of the extravaganza.
Figure 1: Visibility of the Eclipse worldwide.
The eclipse will be visible for all or most of Asia and all of Australia. In the United States, the best viewing will be in the West (lucky us!)
A lunar eclipse can only happen when there is a full moon.
Figure 2: A lunar eclipse happens when the earth is between the moon and the sun.
With the earth right smack in the middle of the sun and the moon, the sun's rays are blocked by the earth. In essence, the earth casts a shadow on the moon.
There are two types of "shadows", or two parts of the earth's shadow, if you will. The penumbra and the umbra.
Figure 3: The earth's shadow has two parts, the penumbra (less dark) and the umbra (dark!).
On Saturday morning, the moon will BEGIN to enter the penumbra at 4:33AM MST (Tucson Time). This portion of the eclipse is often tough to detect.
The eclipse will become easier to notice and observe when it begins to enter the partial phase (or the portion of the shadow that's darkest - the umbra). This will happen beginning at 5:45AM.
Figure 4: The moon begins to enter the umbra at 5:45AM Saturday. This is when the PARTIAL LUNAR ECLIPSE begins.
Figure 5: The moon enters the TOTAL eclipse phase at 7:06AM.
When the moon is in totality, don't expect it to become invisible. Usually, the moon will look orange or red, like in figure 6 below.
Figure 6: An image of the moon in total eclipse (in the TOTALITY phase, where all of the moon is in the UMBRA.)
Before the moon begins to leave totality phase (or the UMBRA), it will set on the western horizon. Since the moon is full, sunrise is exactly the same time as moonset.
Figure 7: The moon will disappear below the western horizon while it is being eclipsed.
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