Eclipses Lunar eclipse
Lunar eclipses
An eclipse half the planet watches together
The Moon enters Earth’s shadow, in view of the entire night side at once.
- Conditions
- Full Moon, with the Moon near a node
- Where it is visible
- The whole night side of Earth
- Total phase
- Up to about 100 minutes
01 / Overview
Meet Lunar eclipses
A lunar eclipse happens at full Moon, when the Moon lies near a node. Unlike a solar eclipse, Earth’s shadow is large enough that the Moon takes more than an hour to enter the umbra completely — and everyone on the night side watches the same event at the same time, with no narrow track to travel to.
Why the Moon turns red
The Moon does not vanish during totality. Sunlight grazing the edge of Earth’s atmosphere is refracted into the umbra; the blue is scattered away en route, and the remaining red light stains the Moon a deep copper. In effect, every sunrise and sunset on Earth is being projected onto the lunar surface at once.
Penumbral, partial and total
The Moon first enters the penumbra, dimming so slightly that the eye often misses it; then the umbra, for a partial eclipse; and once fully inside the umbra, totality. A penumbral eclipse has no umbral stage at all, so there is no obscuration to quote.
02 / Key data
Core parameters
- Conditions
- Full Moon, with the Moon near a node
- Where it is visible
- The whole night side of Earth
- Total phase
- Up to about 100 minutes
- Eye safety
- Safe to watch with the unaided eye
- Recurrence
- Zero to three times a year
Data and calculation notes
Active periods, peak dates and rates are multi-year averages; each year differs a little, so plan against the forecast issued for the year in question.
03 / Observing tips
How to watch
- No filter is needed; binoculars already show the gradations of red.
- The sky darkens during totality, a chance to pick up faint stars near the Moon.
- The observatory’s sky-event planner gives the contact times for each lunar eclipse.
04 / Sources