It’s complete coincidence of course, but there will be a partial eclipse of the Moon on Tuesday 16 July 2019 on the 50th anniversary of the day that Apollo 11 blasted off towards the Moon. The eclipse will be visible from the whole of the UK, though how much of it you see will depend on your location.
A partial eclipse occurs when the Moon passes through the edge of the Earth’s shadow. It can only take place at full Moon, when normally we’d expect to see all the disc of the Moon. But as the Moon moves slowly from right to left through the shadow, it appears as though a circular bite has been taken out of its edge – on this occasion, the upper edge.
However, the event starts before the Moon has started to rise as seen from the UK, though those in countries farther to the east will see the whole event. So we’ll see the Moon rising with a segment already taken out of it. Everywhere that the Moon is visible during the event, people will see the stages of the eclipse looking the same – it is not total anywhere.
As the eclipse progresses, the bite will get bigger until its maximum at 22:30, when the Moon is fully risen from the whole of the UK. Then the Moon starts to move out of the shadow. It’s out of the darkest part of the shadow by midnight, then by 1:20 the following morning it is back to its old shiny self again.
When the eclipse occurs
At this time of year the Moon is always quite low in the sky, and from the middle of the UK it is only about 7º above the horizon at mid eclipse, so you’ll need to find a clear south-eastern horizon to be able to see it. Here are the timings for the progress of the event, which apply wherever you are observing from.
Eclipse begins – Moon enters Earth’s outer shadow (the penumbra): 19:42 BST (Moon below horizon from all the UK)
Moon enters the umbra – the darkest part of the shadow: 21:01 BST (Moon on the horizon from the far south-east of the UK)
Maximum eclipse, with the lunar disc 66% covered by shadow: 22:30 BST
Moon leaves umbra: 00:00 BST
Moon leaves penumbra: 01:19 BST
The time of moonrise varies considerably across the UK. From Dover, the Moon rises at 20:59 while from the middle of the UK it is about 21:20 and from Belfast 21:47. As a quick guide, the Moon rises within a few minutes of sunset, which is often shown on local TV weather forecasts. The Moon will rise directly opposite the sunset.
Observing the eclipse
There’s no scientific value in a lunar eclipse, so it’s simply a great spectacle to watch. Binoculars will help, but you can see all the stages of the eclipse with the naked eye alone (given clear skies, of course!). If conditions are good, the rising Moon is always spectacular, and because it’s low in the sky it often looks reddish because you’re looking at it through a considerable length of the Earth’s atmosphere. And it always appears bigger than when it’s high in the sky, but this is an optical illusion. It’s no bigger than when it’s higher up! The most common explanation is that you judge the size of an object by comparing it with known objects, so when it’s close to the horizon it appears much larger than all the distant objects.
When there’s a total lunar eclipse, and the Moon is completely within Earth’s shadow, the eclipsed area appears reddish. But during a partial eclipse the light part of the Moon is still bright enough to mask any colour in the dark shadow.
If you want to photograph the event, take a look at our helpful guide on photographing the Moon, which will save you a lot of trial and error. It’s not as easy as you might think!
So enjoy the evening – and maybe have a barbecue to celebrate the eclipse and Apollo 11!