Cardiff Astronomical Society

Partial Solar Eclipse - Information provided by the UK Space Agency
On the evening of Wednesday 12th August, the UK will experience its deepest partial solar eclipse for many years. Between about 6pm and just after 8pm in the UK, the silhouetted Moon will slowly drift over a large area of the solar disc, while in a narrow ribbon across the northern hemisphere – running across Spain, the Balearics, Greenland and Iceland, and known as the ‘path of totality’ – people there will see the Sun fully hidden and the associated wonders of a total solar eclipse and the solar corona.

At maximum (partial) eclipse from the UK, the Sun will be a very thin crescent just after 7pm, when it’s sitting about 10-12 degrees above the western horizon. While it might not be a total solar eclipse from the UK, the partially eclipsed crescent Sun will nonetheless be impressive hanging low in the western sky. If we get very clear skies in the west of the country (where nearly 96% of the Sun will be covered) we may be able to perceive a slight drop in light levels, compared to a normal day, around the maximum just after 7pm - though don’t expect this to be anywhere near the effect seen if we were in the path of totality.

Key safety information
Because the Sun is never fully obscured from the UK during this eclipse, there is no point where it is safe to view directly with the naked-eye. You must use a pair of certified eclipse glasses, or a solar filter, conforming to international safety standards [ISO 12312-2:2015(E) if you’re interested] and used per the manufacturer’s instructions; or you can use indirect viewing methods like projecting the image of the Sun onto a piece of card with the Sun behind you. Never look at the partially eclipsed Sun directly, or with any unfiltered optical equipment. And absolutely do not be tempted to use things like sunglasses, welders goggles, negatives etc. as these don’t filter out the harmful, hidden, IR and UV radiation from the Sun that can damage your eyes. If you can’t source a solar filter, then why not try one of the below:

- Join Bridgend Astronomical Society at Porthcawl Rest Bay beach (car park) to safely view the eclipse
- Try a simple pinhole projection setup with a cereal box to see the projected disc of the sun

In the far southwest of the UK the obscuration of the solar disc at maximum will be roughly equivalent to image 1 shown in the carousel below (taken during a total solar eclipse in the Faroe Islands). The second image shows a similar level of coverage (the notch out of the Sun) that we’ll experience at around 6:30pm – albeit it will be in a different position on the solar disc.

For exact timings from your location in the UK you can use the helpful, clickable map on TimeAndDate.com.

How does a solar eclipse occur?
Eclipses like this occur when the planes of the Earth, Sun and Moon’s orbits are aligned so that the Moon’s shadow can fall on the surface of the Earth. This special alignment doesn’t always occur at new Moon, when the Moon is between the Earth and Sun, which is why we don’t see a solar eclipse every month. In a total solar eclipse, the Moon’s shadow has two components that are falling on the Earth: the outer lighter penumbral shadow (which will fall across the UK during the 12 August) and a darker inner core, known as the umbra. It’s where the umbra passes over which determines the path of totality.