Analysis: From meteor showers to constellations, here's what you need to know about observing the summer sky using the unaided eye and binoculars
The summer sky at night from Ireland offers a feast for the eyes. Dominant is the enigmatic Milky Way - our galactic home comprised of 200 billion stars, the collective light from which we see with the unaided eye as a band of white-light spanning the sky.
Stars and their brightness
First, let's talk about the brightness of stars. On a dark night we can see about two thousand stars grouped into constellations with names based on Greek mythology. One star called Vega, in the constellation Lyra and seen directly overhead from Ireland in July, is designated the brightness standard of the sky, with a magnitude of 0. Each magnitude change of '1' means a brightness change of 2.5 times. Brighter stars have negative magnitudes, so a magnitude '-1' star is 2.5 times brighter than Vega, a magnitude '+1' star is 2.5 times dimmer.
The brightest star in the sky is Sirius at magnitude -1.44. Venus can reach magnitude -4.8, the Moon is -12.8 and the Sun -26. In the other direction the faint limit for the unaided eye is +6.5 or about one hundred times dimmer than Vega. The Hubble Space Telescope can see to magnitude +31: 50-billion times fainter than Vega!
Our celestial neighbourhood: May to August
Before we venture deep into the summer skies, let's next look at some relevant local celestial phenomena.
The Summer Solstice
Because the Earth's rotation is tilted by 23o to its orbit, Ireland leans toward the Sun during daylight in summer, giving us long days and short nights.
The longest day of the year is the Summer Solstice, occurring on June 21st this year and delivering a 17-hour day and 7-hour night. Indeed, Ireland doesn't experience official "night" (where the Sun must drop to 18-degrees below the horizon) from mid-May to late July, during which time you'll notice the brightness of the twilight Sun below the northern horizon even during the night. One intriguing gain from this is the occasional appearance of Noctilucent Clouds - high altitude clouds that reflect sunlight from below the horizon, appearing in the northern sky as silvery, rippled clouds in the dead of night.
Lunar matters
To see the Milky Way in all its glory, it matters where the Moon is; with the best Milky Way views when the Moon is new, waxing (just after new Moon) or waning (just before new Moon). A bonus here is that through binoculars the resulting crescent Moon reveals its many craters in detail because their shadows are at their longest. But in preparation of viewing the Milky Way, choose a week before or ahead of the New Moon of June 25th, July 24th or August 22nd.
The planets and Perseid meteor shower in August
Through May and June this year many of the planets are behind the Sun and not on view. Toward August however, Venus, Jupiter and Saturn appear in the eastern sky before sunrise. One spectacle to watch out for is on the morning of August 12th when Venus and Jupiter appear close together in the eastern sky, offering a glistening display for early risers.
Every year the Earth passes through the residue dust trail from comet Swift-Tuttle, which takes 133 years to orbit the Sun; and treating us to a meteor shower called the Perseids which peaks on the night of August 12th. The resulting shooting stars seemingly emanate from the direction of the constellation Perseus, with up to 150 shooting stars seen per hour! To observe, after 10pm, wrap up well and look north toward Perseus, with no equipment needed. A great activity to do with family and friends, where bragging rights reign for whomever saw the brightest one of the evening.
The Milky Way and the summer sky constellations
As the summer unfolds, you'll witness the splendour of the Milky Way running south to north across the sky. Also filling the sky are the several thousand stars that are in fact our close galactic neighbours.
Looking overhead and south are the three summer constellations of Cygnus, Aquila and Lyra. Each possesses one noticeably bright star: Deneb in Cygnus, Altair in Aquila and Vega in Lyra, that form the Summer Triangle. Deneb is in the heart of the Milky Way. Find a comfortable spot to lie down, using a sleeping bag or similar for comfort, and simply look directly up to take in the splendour of it all. Through binoculars, be prepared for breath-taking views of countless thousands of distant stars of the galaxy not visible to the naked eye, reminiscent of a scene from Star Wars.
Further north is Cassiopeia, the giant "W" of the sky, below which is Perseus. To the east are Andromeda and Pegasus - all readily visible once you know where to look. Indeed, you are now gazing into the heart of Greek mythology: queen Cassiopeia, boasting of her daughter Andromeda's beauty, angered the sea god Neptune who sent a monster to ravage their lands. In despair, Cassiopeia chained Andromeda to a rock on the seashore - as prey! But there's a happy ending when Perseus, riding his winged-horse Pegasus, saves Andromeda in the nick of time.
Perseus is, as we've said already, where the Perseid meteors emanate from; but also on view here is a gem of the summer sky: the Perseus Double Cluster. Residing halfway between Cassiopeia and Perseus and just visible to the naked eye, binoculars reveal its true glory as a double cluster of new-born stars. Not far away is the Andromeda Galaxy - just about discernible as a small faint oval of light - the furthest object visible to the human eye at over 2 million light years distance. If you spot it, the light rays you are seeing started on their journey before humans walked the Earth.
A celestial island
As an island on the western edge of Europe beyond which is the Atlantic Ocean, Ireland is blessed with world-class dark skies. This was not lost on our ancestors, nor on us today; exemplified both by magnificent ancient astronomical monuments and precious new space-centres and dark-sky reserves across the island and along the Wild Atlantic Way.
Newgrange is a neolithic monument overlooking the river Boyne in county Meath. Built around 3100BC, the Sun has shone directly into an inner chamber on the shortest day of the year for 5000 years, making it one of the earliest known astronomical monuments. A visit to Newgrange today includes a visit to a wonderful interpretive centre nearby, and indeed entrance to the inner chamber itself.
Move forward to the 19th century and for 70 years Birr Castle in County Offaly hosted the largest telescope in the world. Called The Leviathan of Parsonstown, astronomers from around the world used The Great Telescope to make many important discoveries. Now restored and open to the public on 120 acres of magnificent gardens, one cannot but sense the echoes of our astronomical heritage upon seeing The Leviathan in person.
Indeed, astronomers across our island never relinquished such legacy, and today you can visit a number of exciting astronomy and space centres. Dunsink Observatory in north Dublin is a leading astrophysics institute and invites the public for observing nights from September to May. Blackrock Castle Observatory just a few kilometres from Cork city centre on the banks of the river Lee is also both an astronomical research institute and a wonderful space-centre with exquisite exhibits and events open to the public, with extended hours over the summer.
Armagh Observatory hosts one of the world's premier planetariums with stunning shows. And if choosing a great-outdoors adventure along the western coast, the new Kerry International Dark Sky Reserve and Mayo Dark Sky Park run astronomy viewing events and offer extensive guidance on how to avail of our world-class dark skies where on clear nights, better viewing of the night sky cannot be experienced anywhere else on Earth.
We experience many cloudy nights in Ireland, but we are graced with ample clear nights where our naturally dark location and just a little know-how offer transformative views of the heaven's above.The summer sky in particular is a treasure trove even to the unaided eye, forever rewarding your explorations, a reminder that the Great Outdoors - the Grand Universe itself - is but a 'look upwards' away.
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The views expressed here are those of the author and do not represent or reflect the views of RTÉ
