Analysis: The autumn night sky in Ireland is an observer's treasure-trove and the first celestial event of the season arrives on September 7 with a lunar eclipse and blood moon
Spending even a few minutes gazing at a starry night or at our faithful Moon can be both humbling and empowering, connecting us with the grand stage of the cosmos itself. As my dear friend Dr. Niall Smith, founder of Blackrock Castle Observatory in Cork points out: you don't need to go into space to experience the overview-effect, just look up at a blanket of stars on a clear night to experience the grandeur of the Universe of which we are each a part.
There is also satisfaction in discovering for ourselves something of the make-up and clock-like movements of the sky, and of the countless celestial objects within it. As a matter of cosmic origins, Earth both rotates on its axis eastward and orbits the Sun eastward; and so, our perception of the movement of the sky itself is to witness everything rise from the east and set in the west, daily through Earth's rotation, and yearly because of its orbit about the Sun.
So on any given night you will see, even over a few hours, a constellation move from east to west. But watch it nightly over a few weeks and you will also notice it rise earlier from the east and set earlier westward as we move along our orbit about the Sun.
No clearer is this yearly drift of the constellations westward than in the autumn sky over Ireland. We've enjoyed months of glorious constellations, such as Cygnus, Aquila and Lyra nested in the Milky Way overhead each night, but by now noticeably drifting westward earlier in the evenings. Meanwhile the winter constellations Taurus and Orion - behind the Sun during the summer - are now coming round from the east late at night, giving us our first glimpse of the winter sky to come.
The Autumn Sky
And so the autumn sky represents a hand-over from summer to winter; but still, including the best of both: early evening for summer constellations, late night anticipation of the winter sky. And for observers new, experienced, young and old, conditions are good: the nights getting longer so better even for youngsters before bedtime, yet not too cold as to be a deterrent.
Accompanying this seasonal change are the circumpolar constellations high in the sky all year round. We mentioned some in our summer piece: Cassiopeia, Pegasus and Andromeda - all now overhead and gloriously visible. Finding Cassiopeia the great 'W' is a stirring moment; while Pegasus, which contains a gigantic square of four stars directly overhead, is so obvious you'll wonder how you missed it - once you find it for the first time, that is! The huge size of constellation often surprises new observers, so forget binoculars and telescopes - just look up: they're directly in front of you.
The Plough
One of the oldest constellations - included in a list by Ptolemy himself - is Ursa Major or Great Bear, the brightest part of which we call The Plough. In mythology Ursa Major was Callisto, beautiful servant to the goddess Juno whose jealousy spurred Juno's husband, Jupiter, to protect Callisto by turning her into a great bear! Arcas, Callisto's son, intent on killing it, was also turned into a bear by Jupiter, placing both in the sky as Ursa Major and Ursa Minor, the constellation containing the Pole Star, Polaris.
Although Ursa Major is a challenge to identify, the Plough is easily seen high in the north sky. It is also an excellent signpost constellation: its front two stars point toward Polaris and continue to Pegasus and Cassiopeia; meanwhile its handle points toward the red-supergiant star Arcturus, among others.
Celestial Events: September to December
While constellations are permanent, there's also a plethora of activity occurring in the sky: planets wandering through the Zodiac as they circle the Sun, lunar eclipses that dim the Moon as it passes through Earth's shadow, meteors as Earth passes through dust trails from comets, and conjunctions as the Moon passes close to more distant planets and stars.
These wondrous events reveal the perpetual motion of the universe - the harmony of the spheres - which over time have inspired myths and love songs, and profound astronomical discovery. This autumn will not disappoint:
Lunar Rendezvous
September 7, 2025 brings a lunar eclipse. Here, the full Moon passes through the Earth's shadow. Our atmosphere scatters blue light (why the sky is blue), leaving only the Sun's red light to illuminate the Moon as it passes through the Earth's shadow. It will be an arresting sight just before 8pm on Sunday evening, when a blood-red Moon rises above the eastern horizon. The eclipse lasts until 10pm, when it returns to full brightness exiting the Earth's shadow. Look carefully to see the curvature of Earth on the Moon.
The Moon beguiles again before sunrise on September 19, 2025 when in conjunction (close approach) with both Venus and Regulus, the brightest star in Leo the Lion. A beautiful event to witness for early risers: look east after 5am.
September 22, 2025 is the autumnal equinox, when Earth is tilted neither toward nor away from the Sun, meaning a 12-hour day and 12-hour night, after which the nights are longer than the days until the next spring equinox. October 7's Harvest Full Moon is also a Supermoon, meaning it is closest to the Earth and appearing 14% larger and 30% brighter. This coincides with World Space Week from October 4th to 10th, where in Ireland you'll find hundreds of events.
Orionids Meteor Shower
October 20, 2025 brings the Orionids Meteor Shower as Earth passes through the dust trail of Halley's comet. While not spectacular, it will be excellent to watch this year because the Moon is not up. To observe, rap up well and head out when dark. No equipment is needed: just look south-east toward Orion and with a little patience you will see about 20 shooting stars criss-crossing the sky every hour!
Planetary Giants
Toward November the two giant planets Jupiter and Saturn appear in the southern sky after about 9pm. Jupiter in the constellation of Gemini, Saturn in Pisces. Both appear as golden star-like objects but do not twinkle because we are seeing them as tiny discs in the sky, and not star-like points of light.
Saturn is intriguing through a small telescope because its rings are currently edge-on to Earth and appear as a thin line of light across the equator of the planet. Jupiter is spectacular through binoculars or a small telescope where you’ll also see four bright points of light: the four large Galilean moons Io, Europa, Callisto and Ganymede that spurred Galileo to ponder that if they orbit Jupiter, perhaps Earth orbits the Sun - an idea for which he was placed under house arrest for the final nine years of his life.
Geminids Meteor Shower
We round off this whistlestop tor of the autumn night sky with our first glace into the December winter sky. By now the winter constellations of Orion, Taurus and Gemini are in full view looking south, and on December 14th the spectacular Geminids meteor shower will peak - delivering about 120 shooting stars per hour. Look south toward Gemini after dark.
Winter Solstice
The Winter Solstice - the shortest day of the year in the northern hemisphere on December 21st - has been spectacularly marked in Ireland for 5000 years by the neolithic tomb Newgrange in County Meath, when the Sun shines into its inner chamber at sunrise. Consider a visit to Newgrange on the winter solstice where it bestows a potent sense of renewal as we head toward the new year.
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
