Europeans, Africans, Asians and Australasians will be able to watch the Earth’s shadow pass over the Moon this evening, as 2020’s eclipse season resumes.
A fine penumbral lunar eclipse will be visible on Friday, June 5 to most regions of the world, marking the second of four lunar eclipses to be expected this year, and the last to be visible from the UK.
But what will it look like, and how do you catch it? What even is a lunar eclipse, and a penumbral one at that?
Here’s your guide to Friday’s astronomical event.
How to watch the lunar eclipse
The eclipse will begin on June 5 at 6.45pm BST, and it expected to finish at 10.04pm.
Lucky Brazilians may catch a glimpse, along with West Africans and Europeans, at moonrise in their countries. East Africans and Asians will see the entirety of the eclipse, while Central and North Americans will have to wait till the next eclipse, which will happen on July 5.
Meanwhile, for those in the UK, the eclipse will reach its greatest visible magnitude at 9.06pm, so head outside beforehand.
Since the moon will be near the horizon at the point, it's a good idea to head high if possible, and seek out clear views to the southeast.
However, be aware that the weather could obscure view, as most places in the UK can expect to see at least some cloud covering.
What will it look like?
Truthfully, not a whole lot different from usual, as the moon will very much still glow.
This eclipse is a penumbral one, so the effect is subtle and the moon may not look much different from a full moon. Rather than the Earth’s main shadow – the umbra – covering the moon, penumbral eclipses involve the weaker, outer shadow passing, meaning the visible change is only slight. The eclipsed segment of the moon will be faintly darker than the rest of it.
The most impactful moment of Friday’s eclipse will saved for viewers in the remote sea off the eastern coast of Madagascar – presumably a very intimate audience – and, in fact, the effect will be rather more dramatic from the moon's perspective, as the Earth comes to partially eclipse the sun.
Lunar eclipses explained
A lunar eclipse occurs when the Earth passes directly between the Sun and Moon, casting a shadow over the latter.
The irregularity of these is explained by divergence between the Moon’s orbit and the Ecliptic Plane, which is the line that would circle the Earth if we traced in pen the Sun’s route across our sky; essentially, it is our solar orbit.
If the Moon orbited exactly along this line, we would have two eclipses each month — one lunar and one solar.
Instead, the Moon’s orbit is inclined about five degrees relative to the Ecliptic Plane. Consequently, the number of orbits we see varies year by year.
One calendar year has a minimum of four eclipses, as with this year; in 1982, there were seven.