How a lunar eclipse works
At full moon, the Moon can pass through Earth's shadow. The pale outer penumbra causes subtle dimming, while the darker umbra produces a partial or total lunar eclipse.
Because Earth's shadow at lunar distance is much larger than the Moon, the event lasts far longer than solar totality and is visible from most of Earth's night side.
Penumbral, partial and total
- Penumbral: the Moon crosses only the diffuse outer shadow; the change can be difficult to notice.
- Partial: a dark curved edge of Earth's umbra moves across part of the Moon.
- Total: the entire Moon enters the umbra and often turns copper, orange or red.
Why the Moon turns red
Sunlight passing through Earth's atmosphere is refracted into the umbra. Blue wavelengths are scattered more strongly, while red and orange light reaches the lunar surface. The same effect colours sunsets.
The exact shade depends on clouds, dust and aerosols around Earth's limb at the time of the eclipse.
How to observe and photograph it
- No eye protection is required; binoculars and telescopes are safe.
- Use a tripod and manual exposure because the Moon becomes much dimmer during totality.
- Include a landmark or landscape to show scale and place.
- Check moonrise, moonset and local weather as well as the eclipse contacts.
Scientific references
References used for eclipse dates, safety guidance and local calculations.