Article by John Flannery.
Parts of Ireland will have the unusual experience of dusk appearing to fall twice on the evening of August 12th when the deepest partial solar eclipse in eleven years will be seen across the country as more than 90% of the sun is obscured by the moon.
The best views will be in the southwest where just a tiny sliver of sunlight remains mid-eclipse.
Circumstances are not as good again for us until a total solar eclipse in 2090, which again favours the southwest.
Safety first
While there will be a lot of interest in this partial, eye safety is paramount should you plan to take a look, as the fraction of sun remaining mid-eclipse is still unsafe to stare at directly without taking proper care.
However, practical and safe ways to watch the show unfold are described in a booklet at https://eclipse26.ie (compiled by DIAS Dunsink Observatory and ESERO Ireland), or at https://tinyurl.com/33ydbhdx (TimeAndDate’s website).
Certified eclipse glasses have filters made with special material to reject the sun’s dangerous energy across various wavelengths but check for any pinholes first by holding them up to a light, and discard if you notice any scratches.
Polarised sunglasses, aluminum foil, or similarly opaque items on the other hand do not offer the same protection, nor dim the sun sufficiently, and should not be used.
Without taking proper precautions, there is a risk of permanent eye injury due to thermal retinal burn (your eye’s retina has no pain receptors, so you are unaware as the harm is being done).
On no account should you attempt to look at the eclipse with any binoculars, telescope, or spotting scope unless they are specifically designed for solar observing. Wearing eclipse glasses while attempting to look through any optical instrument is highly dangerous and guarantees very severe and permanent eye injury.
If in doubt, then several astronomy clubs and facilities countrywide have coordinated eclipse viewing events with the details listed on their respective websites.
These include Armagh Observatory, Ballycroy Visitor Centre (Mayo), Birr Castle Demesne, Blackrock Castle Observatory (Cork), Dunsink Observatory in Dublin, NUI Maynooth’s Department of Physics, the Irish Astronomical Society (Phoenix Park Visitor Centre), the Irish Astronomical Association in Belfast, and Midlands Astronomy Club. Other groups will list events on the website of The Irish Federation of Astronomical Societies at www.irishastronomy.org
Eclipse science
The eclipse this August is total on a narrow track that initially favours some countries ringing the Arctic before the moon’s umbra passes about 220 kilometres off our coast. A broader area outside the central path sees a partial eclipse.
The shadow next makes landfall in northern Spain before curving towards the country’s Mediterranean coastline where the eclipse ends with a stunning totality just minutes before sunset from the Balearic Islands.
That our experiences of total solar eclipses is possible at all is due to a remarkable coincidence found nowhere else in the solar system. The sun is roughly 400 times the diameter of the moon, but is also about 400 times more distant, meaning both appear the same size in our sky.
Every eighteen months or so, the two bodies align when the moon is at a new phase and we get a solar eclipse of one type or another. The moon’s orbit is tilted slightly with respect to the Earth’s plane though which is why we do not get an eclipse every month.
Partial expectations
Our table lists the start, mid-, and end times for different locations around Ireland, with mid-eclipse soon after 7pm. A reasonably clear western skyline will allow you to watch the proceedings as the sun starts to get low.
Changes in the ambient light level will only become apparent though when the sun is nearly 80% obscured. That is often experienced as an abrupt fall in brightness as our eyes compensate for the changing light levels in a logarithmic way rather than linearly.
As the eclipse deepens further, your surrounds can take on a strange hue, as if colour is being bled out of the landscape. This transformation takes place as our eyes shift from daylight/colour perception towards night/monochrome vision.
Shadows are now becoming noticeably sharper too.
One way to demonstrate that is to hold your hands at right angles to each other: the shadows cast that lie at right angles to the orientation of the sun’s crescent remain blurry, whereas those aligned with the sun’s narrowing crescent are sharper.
Multiple eclipse crescents will also be seen dappling the shaded ground beneath trees (throw down a white sheet for better contrast), or they can be projected with a colander or kitchen strainer. It’s a neat way for everyone to track the narrowing solar crescent.
By mid-eclipse the sky will appear darker than expected, but the light levels are still generally equivalent to a heavily overcast winter’s day, or ten to twenty minutes before sunset on a clear evening. The sun’s low altitude at this time may have an impact on what we anticipate though.
From locations in the far southwest of the country, where the sun is almost 98% eclipsed, the more pronounced darkening of the sky will likely cause some streetlights to automatically switch on, while birds will start to roost early. The brilliant planet Venus will pop into view at some stage to the far left of the sun as mid-eclipse approaches.
Unless equipped with a suitable filter, most smartphone cameras will struggle to record this eclipse because either the image scale is still too small for some at their maximum zoom, or the brightness of the remaining bit of sunlight will overwhelm the sensor. Certain apps will allow you to adjust internal settings though, so some good results are possible with a little experimentation.
From a science perspective, an app called Physics Toolbar Sensor Suite comes with a light meter option to let you take lux measurements during the various stages of the eclipse. Take note of any temperature drop too, while the output from solar panels will also dip somewhat.
Following mid-eclipse, as the sequence of events takes another hour to play out in reverse, the thoughts of regular eclipse chasers generally begin to turn to the next occasion when we can stand in the shadow of the moon.
Amazingly, Spain gets another total solar eclipse in August 2027 after this one, and an annular in January 2028 – it is rare for one country to get three solar eclipses in quick succession. Next year’s totality is the second longest of the 21st century too and lasts almost six-and-a-half minutes from Luxor in Egypt.
August’s other celestial highlights
The August 12th solar eclipse also coincides with the maximum of the Perseid meteor shower, offering a moon-free and darker sky to see one of the best shooting star displays of the year.
Perseus, where the meteors appear to diverge if you trace their path back, rises in the northeast as night falls and climbs higher in the sky as the hours pass. You should see 40 or more meteors per hour from a rural location during the peak.
A lunar eclipse almost always precedes or follows a solar eclipse by a fortnight, and we get a deep partial in the early hours of the morning of August 28th prior to moonset. The area of the moon immersed deepest in the earth’s shadow then will take on the typical orange-brown hues of a lunar eclipse. Binoculars will enhance the view.
Should you take the opportunity to travel to totality this year, next, or in future years, then it is worth reflecting on how eclipses are no longer a mystery or feared. Yet they still convey that same sense of insignificance in a vast cosmos as they did in the past.