There is a total solar eclipse next week – but, here in Cork, we’ll see a partial eclipse. On the evening of 21 August, the Moon will partially cover the Sun, look for a little sliver of the Sun ‘missing’ – the maximum eclipse for us is around 8pm. It will not be anywhere near as striking as the partial eclipse of March 2015 – see here for what can be expected. To check visibility for your own location, use this interactive map.
An eclipse of the Sun can only occur at New Moon – when the Moon passes between Earth and Sun. Since New Moon occurs every 29 1/2 days, you might think that there would be a solar eclipse each month. But this doesn’t happen because the Moon’s orbit around Earth is tilted at an angle to the Earth’s orbit around the Sun. As a result, the Moon’s shadow usually misses the Earth – passing above or below our planet at New Moon. But, at least twice each year the geometry does line up just right so that an eclipse of the Sun is seen from some part of Earth. In 2018 there will be three solar eclipses – all of them partial.
It is never safe to look at a partial eclipse, since our eyes’ automatic blink reflex in response to bright light may not kick in, so we look at the Sun, keep looking at it and take in too much light. There are no pain receptors on the back of the eye – so an injury can occur without you being aware of it. Even when 99% of the Sun’s surface is covered by the Moon, the remaining crescent Sun is still intense enough to cause a retinal burn – and the eclipse next week will have most of the Sun exposed.
Proper filters that can block out enough of the damaging rays should be used if you want to look directly at the Sun, but make sure they are designed for this. Poorly made filters may crack or not offer protection and the fact that the Sun appears dim, or that you feel no discomfort when looking at the Sun through the filter, is no guarantee that your eyes are safe.
The safest and most inexpensive way to see a partial eclipse is by projection, use a pinhole or small opening to cast an image of the Sun. Simple pinhole cameras can be made with a shoebox and a bit of metal foil with a tiny hole punched in it. Or hold up a colander in front of a white card and look for the shape of the Sun in the many small shadow images produced on the card (Yes, really!). Binoculars can also be used to project a magnified image of the Sun on a screen, but don’t be tempted to turn the binoculars around to check on the Sun directly. If you want to capture the event on camera – be sure to use a decent filter – or risk damaging your equipment.
In many cultures a total eclipse is seen as an event to be feared – in particular for the astronomers in the apocryphal Chinese story – who failed to predict an eclipse in 2000 BC because they were drunk:
“Here lie the bodies of Ho and Hi,
Whose fate, though sad, is risible;
Being slain because they could not spy
Th’ eclipse which was invisible.”
If it is cloudy, start planning for the next total eclipse – 2 July 2019, but you’ll have to travel to South America.
To watch the total eclipse book a flight, or watch here.