The Double Cluster in Perseus, the Heart Nebula, the Soul Nebula, and nearby star clusters
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Perseus is one of the larger constellations in the northern sky, ranking 24th in size among those recognized today. It belongs to the group of autumn constellations and is most prominently visible from mid-latitude regions, such as Poland, during that season. The number of stars visible to the naked eye in this constellation is estimated to be around 90. Perseus is also one of the 48 constellations described by Ptolemy.
According to ancient Greek mythology, Perseus was the son of Zeus and Danaë and one of the greatest heroes in Greek lore.
The king of Argos, Acrisius, had been told by an oracle that he would die at the hands of his own grandson. After Perseus was born, the king had his daughter Danaë and her child sealed inside a chest and cast into the sea in an attempt to prevent the prophecy from coming true. However, Zeus ensured that the chest washed ashore on the island of Seriphos, where Diktys, the brother of King Polydectes, took them in. As Perseus grew up, Polydectes sent him on a seemingly hopeless quest to obtain the head of the fearsome Medusa, the youngest of the Gorgon sisters, Stheno and Euryale, whose gaze could turn anyone who looked at her into stone. With the help of the gods, Perseus received several divine gifts: winged sandals, a magic pouch, and the Helmet of Invisibility from the nymphs, a steel sickle from Hermes, and a polished shield from Athena. Using these, he succeeded in beheading Medusa. From her blood sprang the famous winged horse Pegasus, who was later ridden by Bellerophon. On his way back through Ethiopia, Perseus rescued the beautiful princess Andromeda from a sea monster called Cetus. He then took her to Seriphos as his bride. Upon returning to the island, he discovered Polydectes’s treachery and used Medusa’s head to turn the king and his court to stone. Perseus later traveled with his wife and mother back to his homeland of Argos. During an athletic competition, an accidental throw of a discus struck his grandfather’s head, fulfilling the prophecy. After his death, Perseus was placed among the stars by the gods, alongside Andromeda, her parents Cassiopeia and Cepheus, as well as Cetus and Pegasus.
Within the boundaries of the constellation Perseus lie many fascinating deep-sky objects. Several of them are described in the following observations.
Observations
September 15, 2020, around 11:30 PM – Jaworzno (Poland)
suburban conditions, high level of light pollution
That night, the sky was occasionally a bit hazy, and at times there were some passing clouds. Undeterred, I went out to my garden to enjoy the view of the night sky. After setting up my equipment, I noticed that the region of Perseus appeared to be free of clouds, haze, or any atmospheric disturbances that could hamper observations. Consequently, I managed to gather enough data, which resulted in Photo 1.
The photograph shows a region of the sky near the boundary between Perseus and Cassiopeia, as indicated by the presence of both Eta (η Persei), known as Miram, and Epsilon (ε Cassiopeiae, or Segina), where the hero’s hand holding a sword was traditionally imagined. There are so many interesting objects visible here that it is difficult to decide which one to start with.
NGC 663 (Caldwell 10) is a young open cluster formally located within the boundaries of Cassiopeia. It was discovered by William Herschel on November 3, 1787, and lies about 8,000 light years from the Sun. The cluster contains around 400 stars, estimated to be roughly 20 to 25 million years old. It includes at least five so-called blue stragglers, stars that appear significantly hotter and bluer than others of similar brightness, making them seem much younger.
Another comparable object is NGC 1027, which is closer at just over 3,000 light years away. It too was discovered by Herschel in 1787. NGC 1027 is an open cluster in Cassiopeia that lies between two emission nebulae but is not physically associated with them. Its brightest star has an apparent magnitude of about 9.3m.
A similarly intriguing object is the open cluster Stock 2. Its stars are spread out rather loosely, and the cluster’s angular diameter can reach up to 1°, about twice the size of the full Moon. It lies roughly 1,050 light years from Earth. The cluster’s overall brightness is usually given as about 4.4m, but with a good pair of binoculars (10×50 is sufficient, though 15×70 is better), one can discern around 20 stars of approximately 8m. Many observers find that this cluster, sometimes nicknamed the Muscle Man or the Ballerina Cluster, resembles a stylized human figure, shown schematically in Photo 2.
This collection is relatively understudied. The cluster’s age is estimated at 450 ± 150 million years, and the average mass of its stars is around 2.8 M⊙.
A delightful surprise was that, in addition to star clusters, the simple photographic technique I used also captured as many as three nebular objects: the Heart Nebula, the Fish Head Nebula, and the Soul Nebula.
The Heart Nebula (IC 1805) is both an H II region and an emission nebula located in the Perseus Arm (one of the spiral arms of our Galaxy). This nebula, which resembles the human heart symbol (Photo 3), lies about 7,500 light-years from Earth and spans roughly 200 light-years.
Its vivid red glow is primarily produced by hydrogen (H2), the most abundant element in the Universe. At the center of the Heart Nebula lies the open cluster Melotte 15, a very young group of stars only about 1.5 million years old. This cluster contains several bright OB-type stars with masses up to 50 times that of the Sun, along with many fainter stars that possess only a fraction of the Sun’s mass.
Right next to the Heart Nebula is the Fish Head Nebula (IC 179), another emission nebula. It is part of a complex star-forming region located along the edge of a large molecular cloud in the Perseus Arm of the Milky Way.
The Soul Nebula (IC 1848) is in many ways similar to the Heart Nebula. Like its neighbor, it is an H II region and an emission nebula. However, it lies slightly closer to us, at a distance of about 6,000 light years. The designation IC 1848 also refers to the associated open cluster discovered by Edward Barnard in the late 1890s, which illuminates the nebula and has an apparent magnitude of about 6.5m.
The Double Cluster in Perseus occupies the 14th position (Caldwell 14) in the catalog compiled by the renowned amateur astronomer and science communicator Sir Patrick Alfred Caldwell-Moore. It is also known as the Sword Handle or h+χ Persei.
The Double Cluster, consisting of the two open clusters NGC 869 and NGC 884, was first recorded by the Greek astronomer Hipparchus. It was almost certainly observed much earlier, however, since it is easily visible to the naked eye under favorable conditions.
Both clusters are located more than 7,000 light years from Earth but lie very close to each other, separated by only a few hundred light years. They are also similar in age, as inferred from the properties of their member stars. These are relatively young groups: NGC 869 is about 5.6 million years old, while NGC 884 is approximately 3.2 million years old. Both clusters are moving toward Earth at a speed of just over 20 km/s.
Each cluster spans an angular size roughly equal to the apparent diameter of the full Moon. NGC 869 is brighter, more compact, and contains more stars than NGC 884. Most of the stars in these clusters are blue-white, but in and around NGC 884 there are several red giants. Through binoculars, one can see a curved stream of stars extending toward the previously mentioned cluster, Stock 2.
The Double Cluster in Perseus has also appeared in literature. In the People as Gods (Люди как боги) novel cycle by Soviet writer Sergey Snegov, this region is described as the home of the malevolent Demiurges who threaten humanity.
Photos 1, 2, 3 Parameters: Photo 4 Parameters:
Marek Ples