Overnight into Friday morning, the Moon slid almost entirely into the Earth’s shadow. At greatest eclipse, 04:13 UTC on 28 August, 96.3 per cent of the lunar disk sat inside the umbra — the part of the shadow where the Sun is completely blocked by the Earth. A thin silver crescent stayed in direct sunlight the whole time.

That last four per cent is why this was, technically, a partial eclipse and not a total one, and why the widely used phrase “blood moon” was not quite right.

Umbra, penumbra, and why the difference shows up in photographs

The Earth casts two shadows into space. The penumbra is the outer, weaker one, where the Sun is only partly hidden; a Moon inside it dims slightly and most people would not notice. The umbra is the dark core.

Every lunar eclipse begins and ends with a penumbral phase. This one ran from 01:23 to 07:01 UTC in total, with the visible umbral phase — the part where a bite is taken out of the Moon — between 02:33 and 05:52.

The shadowed portion did turn a deep orange or copper colour. That happens because the only sunlight reaching the Moon at that point has passed through the Earth’s atmosphere, which scatters away most of the blue and lets the red through. It is, in effect, every sunrise and sunset on Earth projected onto the Moon at once.

In a total eclipse the whole disk takes that colour. Here, the sunlit sliver stayed bright enough to compete with it, which several photographers argued made for a more striking image than a total eclipse: two very different surfaces on the same object at the same time.

Who could see it

The deep phase was visible from the Americas — apart from Alaska and north-western Canada — along with western Europe and western Africa. In North America it happened late on the evening of the 27th; in Britain and western Europe it fell in the small hours of the 28th, with the Moon low in the western sky around 5am and setting shortly afterwards, so an unobstructed western horizon was essential.

Unlike a solar eclipse, none of this required eye protection. A lunar eclipse is simply the full Moon getting darker, and the full Moon is safe to look at.

The long wait now begins

This was the deepest partial lunar eclipse anywhere on Earth since September 2024, and by most measures the most impressive lunar eclipse of any kind until the end of 2028. The next partial eclipse, in January 2028, will put barely two per cent of the Moon into the umbra — the sort of event only an instrument notices. The next total lunar eclipse falls on 31 December 2028, and will favour Europe, Africa, Asia and Australia rather than North America.

Friday’s eclipse belongs to a family called Saros 138. Eclipses in the same saros repeat every 18 years and 11 days, with near-identical geometry. The previous member of this series occurred in August 2008; the next arrives in September 2044.

It is a useful reminder of what an eclipse actually is. Not an omen and not a rarity, but a piece of clockwork that has been running for a very long time and will keep running, whether or not the sky is clear where you happen to be standing.

Sources

NASA Scientific Visualization Studio; NASA eclipse data (Fred Espenak); timeanddate.com; EarthSky; Space.com.