Moon
Lunar Eclipses: Why the Moon Can Turn Red
Learn what Earth's shadow does to a full Moon and why a lunar eclipse is different from an ordinary phase.
Prepared with AI assistance using the primary sources linked below. How Astroboat works
Earth casts the shadow
A lunar eclipse occurs when Earth lies between the Sun and a full Moon and the Moon enters Earth's shadow. It does not happen every full Moon because the Moon's orbit is tilted relative to Earth's path around the Sun. Most months, the alignment misses the shadow.
Earth's shadow has a darker central region, the umbra, and a lighter outer region, the penumbra. A penumbral eclipse can be subtle. A partial eclipse places only part of the lunar disk in the umbra; during totality, the entire disk enters it.
Why red light reaches the Moon
During totality, some sunlight passes through Earth's atmosphere and is bent into the shadow. The atmosphere scatters shorter wavelengths more strongly, leaving more red and orange light to illuminate the Moon. Dust and clouds in the atmosphere influence the final appearance.
The phrase blood Moon is a popular nickname, not a separate scientific category or a promise of a particular shade. One eclipse may look coppery while another is much darker.
Watch without solar filters
Unlike direct solar viewing, observing the Moon during a lunar eclipse does not require eclipse glasses. Eyes, binoculars, and a telescope are all useful. Check whether the Moon will be above your local horizon during the relevant phases; global eclipse times do not guarantee local visibility.
Make a simple sequence of notes: the time, how much of the Moon appears shadowed, and the color you see. In Astroboat's Events section, treat the entry as a prompt to open the original source for a detailed visibility map and timing.