As the Earth makes its annual orbit around the Sun, we are able to see different constellations in the night sky depending upon the season of the year, and our location on the planet. While all observers have their own favorites when it comes to the constellations, the onset of summer in the northern hemisphere brings the return of a familiar crop of constellations which each stargazer will no doubt welcome, albeit for different reasons.
Famously heading the list of summer constellations are three contained within an asterism known as the Summer Triangle, which appears in the east during early evening, before dominating the overhead sky around midnight. The three brightest stars in this arrangement are Deneb in Cygnus, Antlia in Aquila, and Vega in Lyra, with the Milky Way passing between the latter two stars in the triangle.
Not far north-east of the star Vega in Lyra is the constellation of Hercules, which is the night sky’s fifth largest constellation, and whose four main stars form an asterism called The Keystone, although it is sometimes difficult to spot because its stars are all between magnitudes of just 3 and 4.
Meanwhile, low in the southern sky can be found the stunning constellation of Scorpius, which resembles the scorpion which it depicts, and never rises much above the horizon as it makes its way across the summer sky. Scorpius lies on a band of sky reserved for zodiac constellations called the ecliptic, with one of its nearby companions including Sagittarius to its east, which is recognizable by its distinctive asterism known as The Teapot.
Finally, there are five circumpolar constellations that can be observed in the northern hemisphere throughout the year, regardless of the season, which are Ursa Major, Ursa Minor, Cassiopeia, Cepheus, and Draco.
All the summer constellations mentioned above have been covered in detail already on this site, and more information on them can be discovered by following their links. However, in this article I will take the opportunity to explore three of the summer time’s most prominent constellations further, namely Hercules, Cygnus, and Lyra.
Although Hercules has no first-magnitude stars, it is one of the most iconic northern hemisphere summer constellations, dating back as it does to ancient Sumerian times. In fact, Hercules is so old that even the ancient Greek astronomers were somewhat uncertain as to its exact origins. Nonetheless, the constellation is associated with the Roman demigod Hercules, who has an equivalent in the Greek hero Heracles, who in his turn, appears to have been modeled on the Sumerian hero, Gilgamesh.
• Coordinates: Between latitudes +90° and -50
• Best seen: 21:00 (9 p.m.) Local Time during the month of July
• Brightest star: Kornephoros (Beta Herculis)- Apparent magnitude: 2.81
• Stars with planets: 15
• Size: Fifth largest constellation
• Area: 1225 square degrees
• Neighbouring constellations: Aquila, Boötes, Corona Borealis, Draco, Lyra, Ophiuchus, Sagitta, Serpens Caput, and Vulpecula.
Hercules is one of the few constellations that do not require loads of imagination to recognize. The figure of a man-like creature is fairly easy to discern, especially when the Keystone asterism that marks out the figure’s “torso” is identified. Look for the star, Alpha Herculis, (Ras Algethi) atop the Keystone; this star marks out the figures’ head in traditional depictions. One meteor shower, the Tau Herculids, is associated with the constellation.
Objects of Interest
Despite its prominence in the summer sky, Hercules contains relatively few objects of real interest to amateur astronomers. However, it does contain two Messier objects, both of which are spectacular globular star clusters that are easy targets for small amateur telescopes. Below are some details:
Messier 13 (M13, NGC 6205), also known as the Great Globular Cluster, or sometimes as the Hercules Globular Cluster, is 22,200 light years away, 145 light years wide, and contains about 300,000 stars that span a full 20 minutes of arc of the sky. The cluster was included in Messiers’ catalogue in June of the year 1764. In 1974, a message, now known as the Arecibo Message, was transmitted towards M13 in the hope that hypothetical extraterrestrials living in the cluster might one day intercept it. At the time, it was thought that since the star density was a high as it is, there might be a more than even chance that there will be many habitable planets in the cluster as well. However, by the time the message arrives at the cluster in 20,000 years’ time, the cluster will no longer be in its current position.
Messier 92 (M92, NGC 6341) is another perennial favorite of amateur observers because it is relatively easy to find, having an apparent visual magnitude of 6.3. The cluster was discovered by Johann Elert Bode in 1777, but Charles Messier rediscovered it independently a few years later, in 1781. Located about 26,700 light years away, this cluster has an estimated age of around 14.2 billion years, which being about as old as the Universe itself, makes it one of the oldest star clusters known.
Apart from the fact that the brightest star in Cygnus is also the 19th most luminous star in the entire night sky, this constellation is like Hercules, one of few constellations that actually look somewhat like the figure it is named after, which in this case is a swan with outstretched wings. Cygnus also contains the famous (and hard to miss) asterism called the Northern Cross, which is made up of the stars Deneb (Alpha Cygni), Delta Cygni, Albireo (Beta Cygni), Gienah (Epsilon Cygni) and Sadr (Gamma Cygni), marking the centre of the asterism.
• Coordinates: Between latitudes +90° and -40°
• Best seen: 21:00 (9 p.m.) Local Time during the month of September
• Brightest star: Deneb ( Alpha Cygni) – Apparent visual magnitude 1.25
• Stars with planets: 97
• Size: 16th largest constellation
• Area: 804 square degrees
• Neighbouring constellations: Cepheus, Draco, Lacerta, Lyra, Pegasus, and Vulpecula.
Cygnus contains several objects of scientific interest, such as Cygnus X-1, a powerful x-ray source, a spectacular galaxy known as the Fireworks Galaxy (NGC 6946), the Pelican Nebula (IC 5070), the North America Nebula (NGC 7000), the Crescent Nebula (NGC 6888), and the famous Veil Nebula that is so big that various parts of it have their own NGC designations (NGC 6960, NGC6962, NGC6979, NGC6992, and NGC6995). Two meteor showers, the October Cygnids and the Kappa Cygnids, are associated with the constellation.
Objects of Interest
Apart from the beautiful double star Albireo, the constellation only contains two Messier objects, both of which are open clusters, and visible with modest amateur equipment. Below are some details-
Messier 29 (M29, NGC 6913), located relatively close-by at a mere 4,000 light years distant, has an apparent visual magnitude of 7.1, making it an easy target for binoculars. M29 is also relatively young, being only about 10 million years old. The most luminous star in the little cluster has an apparent magnitude of 8.75, and the five hottest stars are all B0-type stars. Look for the cluster roughly 1.7 degrees to southeastward of the star Gamma Cygni.
Messier 39 (M39, NGC 7092), located about 800 light years away, was discovered by Messier in 1764, and is estimated to be between 200-300 million years old, which puts it in the intermediate age bracket for clusters of this type. Having an apparent visual magnitude of 5.5, all the observed stars in the cluster are still on the main sequence, although the brightest stars in the cluster are expected to begin their transition into the red giant phase within the next several million years or so. Look for the M39 about 2.5 degrees to the southward of the star Pi-2 Cygni.
Lyra may be among the smallest constellations, but it has a unique claim to fame, and therefore deserves its place on this list of prominent summer constellations. It contains the star Vega, which is not only its brightest star, but also the second most luminous star in the northern hemisphere, and the fifth brightest star in the entire night sky overall. Moreover, Vega is the first star after the Sun to have its picture taken and its spectrum recorded which happened in July of 1850, and August of 1872, respectively. Another star of interest in Lyra is Epsilon Lyrae, a multiple star system also referred to as “The Double Double”.
• Coordinates: Between latitudes +90° and -40°
• Best seen: 21:00 (9 p.m.) Local Time during the month of August
• Brightest star: Vega (Alpha Lyrae) – Apparent magnitude 0.03
• Stars with planets: 9
• Size: 52nd largest constellation
• Area: 286 square degrees
• Neighbouring constellations: Cygnus, Draco, Hercules, and Vulpecula
Lyra contains several objects of scientific interest, among which is NGC 6745, a trio of galaxies that is caught in a violent merger, and the open star cluster NGC 6791. Three meteor showers, the Lyrids, the June Lyrids, and the Alpha Lyrids, are associated with the constellation.
Objects of Interest
For amateur observers with modest equipment, Lyra offers two Messier objects, one of which is M57 aka The Ring Nebula, which is so well-known that it hardly needs an introduction. The other object is a globular cluster that is well worth observing, since in a large telescope, its stars seem to sparkle like ice crystals; Messier 56 (M56, NGC 6779), located about 33,000 light years away, is a large, 13.70 billion-year-old cluster that stretches across a full 84 light years. With binoculars, this 8.3 magnitude cluster appears as a big, fuzzy star but telescopes of 8-inch aperture will easily resolve the outer fringes of the cluster if seeing conditions are good. Larger instruments resolve more stars, but to see the cluster in all its finery requires an instrument of 12-inch aperture or larger. The most luminous stars in the cluster are all about 13th magnitude, and it contains about a dozen or so known variable stars.