Total, partial and penumbral mean different things
Earth’s shadow has a dark central region, the umbra, surrounded by a lighter penumbra. In the umbra, Earth blocks direct sunlight from the whole solar disk. In the penumbra, Earth blocks only part of it.
A total lunar eclipse puts the Moon completely inside the umbra. A partial eclipse takes only part of the lunar disk through it, producing a noticeable dark bite. A penumbral eclipse misses the umbra and may create only a gentle shading.
“Blood moon” is a popular description usually attached to a total lunar eclipse. It is not a separate scientific eclipse type, and it should not be used to promise a red spectacle for a penumbral event.
Where the red light comes from
Some sunlight passes through Earth’s atmosphere and is bent into the shadow. The atmosphere scatters shorter, bluer wavelengths more strongly, so the light that reaches the eclipsed Moon is often richer in red and orange.
This is related to the warm colors of sunrises and sunsets. It does not mean the Moon produces red light or becomes hot enough to glow. You are still seeing reflected sunlight, with Earth’s atmosphere acting as a filter.
Dust, clouds and aerosols in the atmosphere affect the result. One total eclipse may look coppery and bright; another can be quite dark. Camera exposure and color processing also change the appearance of published photographs.
Do I need eclipse glasses?
No special eye protection is needed to watch a lunar eclipse. You are looking at the Moon, not directly at the Sun. Unaided eyes show the changing shape and color; binoculars can make the boundary of the shadow easier to inspect.
This does not apply to a solar eclipse. The two events have very different viewing-safety rules. Keep that distinction clear when sharing a viewing plan with children or friends.
A lunar eclipse is widespread, but not visible everywhere
Observers on the night side of Earth can see the eclipse if the Moon is above their horizon and the sky is clear. Unlike a solar eclipse’s narrow path of totality, a lunar eclipse is potentially available across a large part of the globe.
The eclipse phases happen at the same absolute instants for observers around Earth, but local clocks show different times. Some locations see the Moon rise already eclipsed or set before the event ends. That makes the local Moon height just as important as the date.
Start with NASA’s upcoming-eclipse calendar, then use a detailed event visibility map. Do not assume an article written for another continent describes your observing window.
A monthly phase is not an eclipse
The ordinary Moon phase changes because we see different amounts of its sunlit half. Earth’s shadow is not responsible for the monthly crescent.
Lunar eclipses occur near full Moon, when Earth can lie between the Sun and Moon. The Moon’s tilted orbit usually carries it above or below Earth’s shadow, which is why most full Moons are not eclipsed.
For a simple observation, sketch the shadow boundary at intervals and note the time zone. If the Moon is low, choose a clear horizon; if cloud arrives, a nearby safe spot with a gap may be more useful than a complicated camera setup.
Sources and image credits
- NASA: eclipses and the Moon. Umbra, penumbra, reddening, safety and orbital geometry.
- NASA: future eclipses. Event calendar and broad visibility areas; distinguish eclipse types before promoting a date.
- NASA: top Moon questions. Normal phases versus Earth’s shadow.
Written for beginners from the sources above. How we research and correct the library. Found an error? Tell us.