Partial solar eclipse
BEST TIME TO SEE: 25 October, 10:00 BST (09:00 UT) until 12:00 BST (11:00 UT)
After what seems like ages since the last solar eclipse visible from the UK – a partial which took place on 10 June 2021
– we get the chance to see a partial eclipse on the morning of 25 October. Partial solar eclipses happen when, from a particular location on Earth, only part of the Sun’s disc is covered by the Moon’s disc. Technically, during such an eclipse, it’s the Moon’s penumbral shadow passing over us.
The amount of the Sun’s disc which is covered is described by two quantities: eclipse magnitude and obscuration. Eclipse magnitude describes how far the eclipsing body extends over the diameter of the object being eclipsed. For example, if the Moon’s edge reached the mid-point of the Sun at the point of maximum eclipse, this would be described as a partial eclipse of magnitude 50%; the Moon covers half the Sun’s apparent diameter. Eclipse obscuration describes
how much area is covered. In our example, where the Moon moves to a position where its edge touches the centre of the Sun’s disc, the obscuration would be 39.1%, assuming the apparent diameter of the Sun and Moon were the same. In practice there are small differences between the apparent size of the Sun and Moon caused by the elliptical orbit of the Moon around Earth and the elliptical orbit of Earth around the Sun.
This partial solar eclipse favours those living further east and to a lesser extent, further north. For example, from Truro in Cornwall the event starts at 10:12 BST (09:12 UT) and ends at 11:38 BST (10:38 UT), a total duration of 86 minutes. The maximum magnitude of the Truro eclipse is 17.66% and obscuration is 8.65%. From Birmingham the eclipse starts at 10:07 BST (09:07 UT) and runs for 101 minutes, with maximum magnitude 25.65% and 14.95% obscuration. York’s starts at 10:06 BST (09:06 UT), lasts for 106 minutes, and shows a maximum magnitude of 29.29% and obscuration of 18.13%. From the northeast tip of Shetland it begins at 10:01 BST (09:01 UT), runs for almost two hours, shows a maximum magnitude of 40.96%, while the obscuration is 29.38%.
As this is a partial eclipse, appropriate filter protection must be used to keep your eyes and equipment safe. Certified eclipse glasses will show the bite taken out of the Sun well. Alternative low-tech visualisation methods include creating a pinhole or similar multi-holed projection setup. A pinhole in a piece of card can be used to cast a shadow onto a light surface, the light passing through the hole being a small image of the Sun. A metal tea strainer makes a surprisingly good shadow-caster for this purpose.