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Weather permitting on Thursday, June 10th, we will see the first partial solar eclipse visible from Ireland since August 2017.
Four years ago, only a tiny nick was taken out of the sun but this month up to 33 per cent of the solar disc is covered by the moon’s silhouette.
The eclipse is annular, or ring-shaped, along a narrow track in Arctic regions, while areas outside that see a partial eclipse with the sun hidden to a lesser extent the further you are from the centre line.
An eclipse is annular if it coincides with a new moon occurring at apogee, or the furthest point in the moon’s orbit around the Earth. The lunar disc is then too small to fully cover the sun mid-eclipse and a ring of light, or annulus, remains. Mid-eclipse is when the maximum percentage of the solar disc is obscured.
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The eclipse will begin at 10am and end at 12.21pm reaching maximum percentage at 11.08am in Dublin. The website timeanddate.com shows the local circumstances along with an animation of the eclipse from start to finish.
Observers will first see a small bite taken out of the sun’s limb which will grow over the next hour to a larger helping. There should not be any noticeable drop in light levels even at mid-eclipse as a large area of the sun’s disc remains uncovered. After maximum, the events then play out in reverse as the moon moves away to return our star to full light.
Eclipse safety
Safety is paramount when observing a partial solar eclipse. Even a quick glance through any unfiltered optical instrument runs the risk of instant blindness.
People have been left with permanent eye damage after wearing ordinary sunglasses or using aluminium or packaging foil as filter material to look directly at a partial solar eclipse. These items do nothing to filter out harmful infra-red wavelengths that can scar your retina without realising it at the time.
Specialised eclipse glasses have energy-rejection filters that allow you view the sun with the unaided eye but for most the only safe way is to project the image via binoculars or a refractor telescope on to a piece of card.
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Tips on how to project the solar eclipse can be found on here, along with other information. In addition, a kitchen strainer can demonstrate the pinhole effect to see multiple solar crescents. The crescents can also be seen under trees where the gaps between leaves act as pinholes.
Eclipse photography will require a proper solar filter securely fitted in front of the lens, while a camera phone will likely overexpose the sun – and run the risk of damaging the sensor. Therefore, taking a snap of the projected eclipse image is probably the best thing to do.
Live-streams
The Dublin Institute for Advanced Studies will livestream the eclipse and feature running commentary by astronomers at Dunsink Observatory and the I-LOFAR radio telescope facility in Birr Castle.
Astronomy Ireland also plan a live-stream, as well as timeanddate.com.
We must wait until the year 2090 for the next total solar eclipse to cross Ireland but June’s event kicks off a remarkable run of a partial solar eclipse visible from our shores every year for the rest of this decade except for 2023. It is an umbraphiles delight.
What you can see in the sky
The moon
Last quarter occurs on June 2nd, new moon on the 10th coincides with an annular solar eclipse (partial from Ireland), and first quarter is on the 18th. Full moon on the 24th is the last of the trio of supermoons for 2021.
The planets
Mercury is not visible this month, but the June evening sky does feature Venus along with a somewhat-subdued Mars.
Bright Venus can be seen a little after sunset low in the northwest where it glimmers in the twilight. The planet is beautifully paired with the thin lunar crescent on the 11th after 10.30pm when it lies to the upper left of the moon. Both then set about 11.15pm.
Two new missions to Venus have recently been granted approval by Nasa and are expected to reach the planet in 2030. The veiled world still has many mysteries including whether volcanic activity continues and why has Venus experienced a runaway greenhouse effect.
The moon is a little further from Venus on the 12th when it is to the planet’s upper left, but the sight is still quite lovely. On the 13th the moon is close to Mars which is currently about as dim as it can get. Look for an orange-tinted “star” to the moon’s lower left that evening.
Jupiter and Saturn require staying up a bit later, but both will rise just before midnight at the end of June. Jupiter lies in Aquarius while Saturn can be found in Capricornus.
The gap between the pair is now quite striking a half year after their very close encounter on the solstice last December. Jupiter moves the equivalent of a full moon diameter in six days. The moon lies between Saturn and Jupiter as they rise after midnight on the night of June 27th/28th.
Jupiter reaches its eastern-most stationary point in Aquarius on June 21st and then begins to retrograde, moving southwest towards the constellation’s border with Capricornus, which it will cross back into mid-August.
Retrograding was a great puzzle to the ancients. It is due to the faster-moving Earth overtaking an outer planet so that it then appears to reverse course for a few months – like an athlete falling behind on a racetrack – before resuming its eastward motion on the sky.
A horrendously complicated system called epicycles was used for a long time to explain the phenomenon and even Copernicus adhered to the arrangement. Johannes Kepler's later work eventually banished their need, though epicycles were not employed either in earlier works by the 12th century Arabic astronomer Ibn Bajjah.
Noctilucent clouds
Noctilucent clouds (NLCs) are the highest-occurring clouds at 83km altitude and can be seen above the northern skyline from Ireland during the summer months between the end of May and roughly mid-July.
The best time to look for NLCs is about 90 minutes after sunset or the same period before sunrise. They remain illuminated by the sun just below the horizon while the world below is still in darkness. NLCs appear silvery-white or electric blue in colour and show a ripple or wave-like structure somewhat akin to cirrus clouds.
NLCs form when water vapour crystalises around specks of meteor dust as temperatures in the mesosphere drop. Nasa scientists have found that 2021 appears to be among the coldest years in that region of our atmosphere for the last 14 years, so they are predicting a good NLC season ahead.
Some preliminary sightings of NLCs have already been reported from Ireland. Martin McKenna's introduction to the phenomenon on his website includes many examples photographed by himself.