How to read an eclipse chart? NASA has a page dedicated to lunar eclipses and provides charts. How are these charts to be read? What do P1, P4, U1,... mean? What about the world map below?



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'P' is the penumbra, the zone where the Earth blocks some, but not all, of the Sun's light from reaching the Moon. 'U' is the umbra, the zone where the Earth blocks all of the light from the Sun (see this primer). As the Moon moves across the two zones then you will get various times as the Moon touches those zones. So P1 is where the Moon just starts to touch the penumbral shadow, U1 is where the Moon just touches the umbral shadow cone, U2 is where all the Moon is inside the umbral shadow and the total eclipse begins. Similarly U4 and P4 are where the Moon last touches the umbral and penumbral shadows. Note that the times in the chart are in Universal Time so you need to account for your timezones' difference from UTC.