From the sky archive · Eclipses
Lunar eclipses from New Zealand
This page first went up in 2005, around the time of a partial eclipse in October that year, and it has been rewritten as a general guide to lunar eclipses seen from Aotearoa New Zealand.
Lunar eclipses are the most relaxed events in astronomy. They happen at night, they last hours, they are safe to watch with the naked eye, and everyone on the night side of Earth sees the same thing at the same moment.
What is happening
A lunar eclipse happens when the full Moon passes through Earth's shadow. The shadow has two parts. The pale outer penumbra only dims the Moon slightly, and a purely penumbral eclipse is easy to miss. The dark inner umbra is where things get interesting. If the Moon only partly enters the umbra, a dark bite appears on one side. If it goes fully inside, the eclipse is total.
Why the Moon turns red
During totality the Moon rarely disappears. Instead it turns copper, brick red or deep rust. The reason is Earth's atmosphere. Sunlight skimming past the edge of our planet is bent, or refracted, into the shadow. On the way through the air, blue light is scattered out, the same process that makes our sunsets red. What reaches the Moon is the combined glow of every sunrise and sunset on Earth at that moment.
How bright and how red the Moon looks depends on what is in the atmosphere. After a large volcanic eruption has lofted fine ash and sulphate high into the stratosphere, eclipses can be very dark. Clean air gives brighter, orange totality.
The Danjon scale
Observers rate total eclipses on the Danjon scale, a simple five-step estimate made by eye:
| L | Appearance |
|---|---|
| 0 | Very dark, Moon almost invisible at mid-totality |
| 1 | Dark grey or brown, detail hard to see |
| 2 | Deep red or rust, with a dark centre and brighter edge |
| 3 | Brick red, often with a bright yellowish rim |
| 4 | Bright copper or orange, with a bluish, very bright rim |
Make your estimate near mid-totality, with naked eyes, and note the time. Comparing notes with other observers is half the fun.
Watching safely
No filters are needed. The Moon is only reflecting sunlight, and an eclipsed Moon is dimmer than normal. Binoculars give the best view of the colour gradients across the disc. A telescope at low power shows the shadow edge creeping across craters. Dress warmly: winter eclipses from New Zealand mean long, cold hours outside.
Photographing a series
A favourite project is a sequence showing the Moon moving through the shadow:
- Use a tripod and a lens of 200 mm or longer for disc detail, or a wide lens for a sequence in one frame over a landscape.
- Expose for the bright Moon early on, around 1/250 s at ISO 200 and f/8, then lengthen exposures dramatically as totality nears.
- During totality you may need 1 to 4 seconds at ISO 800 or more. Without a tracking mount, keep exposures short on long lenses to avoid trailing.
- Shoot at fixed intervals, say every five or ten minutes, so the sequence is even.
- Bracket generously. The brightness changes by thousands of times between full Moon and mid-totality.
Finding upcoming eclipses
NASA maintains a complete catalogue with maps showing where each eclipse is visible and the timing of every phase, at the NASA lunar eclipse page. Times are in Universal Time, so add 12 hours for New Zealand Standard Time or 13 for daylight time. If the Moon is above your horizon during totality, you will see it, cloud permitting, so check MetService on the day. For other effects around the Moon, see our page on moon halos and moonbows.