In the northern hemisphere, the months of July, August and September, are often termed “quiet,” astronomically as the profuse number of bright winter stars in the constellations of Orion, Gemini, Taurus and Canis Major and the spring trio of Leo, Bootes, and Virgo have all disappeared into the western twilight sky.
This seasonal change is brought about by the Earth’s changing position as we orbit the Sun, so as we head into July and beyond, it is noticeable that not only do we get fewer hours of daylight, but the night sky just does not have as many bright stars as the preceding months. Many of the night-sky features visible earlier in the year are still visible but these bright stars and constellations will soon disappear into the evening twilight.
In early July, the evening skies are still dominated by the giant planets, Jupiter and Venus; both still unmistakable in the western sky after sunset. Jupiter is directly below the stars Castor and Pollux in Gemini, which is rapidly receding into the western twilight, which incidentally is notably prolonged in more northerly latitudes. Just above Jupiter but rapidly ascending is the brilliant planet, Venus. Venus is very bright and notably brighter than Jupiter and is higher above the horizon. As Jupiter sets in the west, Venus is rising into the twilight and darkening sky. These two planets were very close to each other on 9 June and passed each other in a spectacular planetary conjunction. Jupiter will disappear into the sunlit sky, go through solar conjunction (behind the sky) on 29 July, and will emerge to be visible in the morning sky from mid-August. Venus, in the meantime, will continue to climb in the evening sky, reaching its maximum elongation from the Sun on 14 August, it will be at its brightest on 18 September, and then pass through inferior conjunction on 24 October.
From an aircraft, both planets and Venus’ elongation will be spectacular for a few weeks. I suggest flight crews on northbound or southbound aircraft advise passengers to look towards the western horizon on and around this date.
Whilst Venus, and to a lesser extent, Jupiter can be seen, even in a light sky this time of year, the stars are not particularly easy to see where the sky does not get very dark—from latitudes above about 50 degrees where we don't go beyond what is termed “astronomical twilight,” which means the Sun is between only 12 to 18 degrees below the horizon.
This does, however, give us the opportunity to see a feature in the sky known as noctilucent clouds (NLC). These are fascinating to see. They tend to be seen best from latitudes between 50 and 70 degrees north, during the period from June to August. Look above the northwestern horizon in the evening sky, an hour or more after sunset or in the northeastern sky an hour or more before sunrise. (In the southern hemisphere they will be seen between December and January.) Quite often spotted, these clouds are very high, about 50 miles above the Earth. They are made of ice crystals that have formed on dust from meteors giving them a silvery, electric-blue, or white glow. They are quite distinctive and tend to exhibit a thin wave-like pattern which is indicative of the strong winds at this altitude.
In the northern skies, the stars of Ursa Major which contain the well-known asterism of the Big Dipper, tend to be difficult to see at this time of year. However, the stars of Cassiopeia sit astride the northern horizon and can be easily identified with a distinctive “W” shape. The two constellations of Ursa Major and Cassiopeia are roughly equidistant to each side of the constellation of Ursa Minor and the Pole star, Polaris (which sits at the northern celestial pole—always the same height above your horizon as your latitudes). Polaris is an age-old useful navigational aid!
The astronomical asterism of the Summer Triangle (or Winter Triangle from antipodean skies) connects the bright stars Deneb in Cygnus, Vega in Lyra, and Altair in Aquila. The relative brightness of these stars is misleading. Vega is 25 light-years away and appears to be the brightest of the three. At magnitude 0.0, it is often regarded as a “standard candle”. Altair at magnitude 0.76 is even closer at 16.7 light-years. Deneb however, at magnitude 1.25, is the faintest of the three but is an estimated distance of 2,600 light-years, so it is the most luminous by far. If you placed all three at a similar distance, Deneb would far outshine Vega and Altair. Deneb’s luminosity is estimated to be 200,000 times that of our Sun. (In astronomy, stellar magnitude or luminosity is measured in a backwards scale—the higher the number, the dimmer the star to our eyes.)
In these lighter nights of summer, the summer constellations of Cygnus (The Swan), Lyra (The Lyre), and Aquila (The Eagle) are joined by Hercules. The strongman will be high in the sky along with the zodiacal constellations of Libra (The Scales), Scorpio (The Scorpion), and Sagittarius, (The Archer) just visible above the southern horizon. Whilst difficult to see, Scorpio is worth the effort as it contains the distinctively red coloured star Antares, one of the largest stars in the sky.
Just above Sagittarius and left of Scorpio are the constellations of Ophiuchus (The Serpent Bearer) and Serpens (The Snake). Serpens is unique among the 88 constellations as it is in two parts—the head (Caput) and the tail (Cauda). Ophiuchus holds the two parts in his hands. Whether the snake is in two distinct parts or if the two are linked behind Ophiuchus is a matter of conjecture. All three are very faint. The brightest star in Ophiuchus is Rasalhague at magnitude 2.08.
The Perseid Meteor Shower
August also brings us the annual spectacle of the Perseid meteor shower. This shower is caused by the Earth on its orbit around the Sun passing through the orbital path of Comet Swift-Tuttle. The shower peaks on 12 August, which fortunately is the same date as the New Moon, so viewing in 2026 may be excellent and you may see up to a meteor a minute, or 60 per hour, which is one of the highest rates for shooting stars annually.
Finally, during September, the Sun heads southwards and will cross the celestial equator on 23 September at 00:05 UTC—the autumnal equinox. There is a popular myth that day and night are precisely equal at the time of the equinox, but this is not truly the case. Atmospheric refraction affects the exact time. While this myth is correct at the equator, the actual date and time of “Equilux” can occur a few days earlier or later, depending on an observer’s latitude.
