The largest-ever gathering of space scientists will take place in Cork this summer

Summer is now truly upon us with the longest day of the year in the Northern Hemisphere occurring on June 21. Since the Winter Solstice in December, the Sun has been rising higher in the sky each day, but on June 21 this behaviour stops and the sun is said to “stand still”. The word ‘solstice’ is derived from the Latin solstitium, from ‘sol’ (sun) and ‘stitium’ (to stop).

One somewhat overlooked consequence of this motion is that the sun never sets very far below the horizon at this time of the year as seen from Ireland, and the night-time skies never fully darken. This is generally not good news for skywatchers as the glow from the sun washes out fainter objects.

The sun is not the only object this month that seems to change direction. The giant planet Jupiter has been moving slowly east against the background stars since roughly February 6, but on June 10 that motion ceases and Jupiter appears to reverse its direction and move westward relative to the background stars. This subtle change of direction might not seem important to the casual observer, but in the words of the science writer Isaac Azimov: “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny...” And this “funny” change in Jupiter’s motion turned out to have huge consequences for our understanding of how our solar system, and ultimately our universe, works.