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NGC 869 and NGC 884 are two bright open clusters in the constellation of Perseus, that are separated by only half a degree of apparent sky. Together they are commonly known as the "Double Cluster" and form a famous showpiece object, that's easily visible to the naked eye and a wonderful sight in binoculars and telescopes. Both clusters have been known since antiquity and probably pre-historically. Greek astronomer Hipparchus first catalogued them around 130 B.C, with early celestial cartographers naming them as "h Persei" (NGC 869) and "χ Persei" (NGC 884).
The Double Cluster is located in the far northwestern part of Perseus, close to the border with Cassiopeia. With a declination of 57N, it's circumpolar from many northern locations and therefore never sets. To locate the object, draw an imaginary line from Mirfak (α Per - mag +1.8) in a northwesterly direction towards the centre of the "W" of Cassiopeia. The Double Cluster lies just over halfway along this line.
It's listed as number 14 in the Caldwell catalogue.
M76, also known as the Little Dumbbell nebula, is a planetary nebula located in Perseus. At magnitude +10.1 and spanning 2.7 x 1.8 arc minutes, it's one of the faintest and smallest objects in the Messier catalogue. The nebula was discovered by Pierre Méchain on September 5, 1780 and first recognised as a planetary nebula by American astronomer Heber Doust Curtis in 1918. However, Isaac Roberts, in 1891, suggested it was similar to the Ring Nebula (M57).
M76 looks like a miniature version of the famous Dumbbell Nebula (M27) in Vulpecula, from which it derives its name. Interestingly, it was assigned two NGC numbers - NGC 650 and 651 - as it was suspected of consisting of two separate emission nebulae. The structure is now classed as a bipolar planetary nebula.
The Little Dumbbell Nebula is faint, but not difficult to locate as it's positioned just south of the prominent "W" asterism of Cassiopeia and a degree north-northwest of Phi Persei (φ Per - mag. +4.0). It's best seen from the Northern Hemisphere during the months of October, November and December. From latitudes 40N or more, the planetary is circumpolar and therefore never sets. However from southern temperate latitudes, it's a difficult object that never climbs high above the northern horizon.
NGC 6541, also known as Caldwell 78, is a globular cluster in the southern constellation of Corona Australis. It shines at mag. +6.3 and therefore just beyond naked eye visibility, but easily seen with binoculars and small scopes. Although often overlooked and not as spectacular as the great southern showpiece globulars, it's still a fine object in its own right.
NGC 6541 was discovered by Niccolò Cacciatore at the Palermo Astronomical Observatory, Sicily, on March 19, 1826. James Dunlop independently found it a few months later on July 3, 1826. The cluster is best seen from southern regions during the months of June, July and August. From locations north of latitude 47N, it never rises above the horizon.
NGC 457 is the brightest open cluster in Cassiopeia and one of the finest objects of its type in the northern sky. At magnitude +6.4, it's just beyond naked-eye visibility but easily seen with binoculars and a beautiful sight through telescopes. The brightest cluster stars are arranged in prominent lines and curves that resemble an Owl shape, hence the popular name "The Owl Cluster".
NGC 457 was discovered by William Herschel in 1787. Finding the Owl Cluster is easy as it's located two degrees south-southeast of eclipsing binary star system Ruchbah (δ Cas - mag. +2.7). This star is one component of the characteristic "W" asterism of Cassiopeia. The brightest star inside NGC 457 is Phi Cassiopeiae (φ Cas - mag. +5.0). Despite not being a member of the cluster, this foreground star is visible to the naked eye. Together with another non-cluster star, seventh magnitude HD 7902 (HIP 6229), they form the bright eyes of the Owl.
NGC 457 is best seen from Northern Hemisphere latitudes during August, September and October. It appears high in the sky and even overhead from many locations. From latitudes greater than 32N, the Owl is circumpolar and therefore never sets.
Astronomers dream of nights where thousands of stars dazzle in pitch-black skies with the band of the Milky Way flowing like a great river from one side to another. Alas for most of us this is often just a dream. We live in towns and cities polluted by artificial lighting from streets, building and factories that significantly diminish our view of the night sky.
However, it's not all that bleak as things do seem to be improving. Recently more efficient street lights have been installed in many areas, significantly reducing the amount of light beamed up to the heavens rather than down on the ground. Of course there are always out of town regions, especially forests and mountainous areas, away from the bulk of civilisation where the beauty of the night sky still rules. But have you ever wondered, how dark are your night skies? One way to check is by looking towards the constellation of Pegasus.
Pegasus is the 7th largest constellation in the sky covering an impressive 1,121 square degrees. For Northern Hemisphere observers, it's easily recognisable during the autumn months. The prominent asterism known as "Great Square of Pegasus" dominates the constellation. It's made up of reasonably bright stars between 2nd and 3rd magnitude:
Scheat (β Peg) - mag. 2.44
Markab (α Peg) - mag. 2.49
Algenib (γ Peg) - mag. 2.83
Alpheratz (α And) - mag. 2.07
M39 is a very loose naked eye open cluster of at least 30 young stars, located in a dense portion of the Milky Way in Cygnus. The cluster is positioned in a beautiful rich region of the sky, with many other open clusters, thousands of stars, regions of dark nebulae, wispy emission and reflection nebulae visible nearby.
The discovery of M39 is an interesting story. It's often credited as one of Charles Messier's original discoveries, which he made on October 24, 1764. However, the discovery has also been credited to French astronomer Guillaume Le Gentil in 1750 and even suggested that Aristotle observed it as far back as 325 BC.
The cluster is relatively easy to find. It's located in the northeastern part of Cygnus, not far from the constellation's brightest star, Deneb (α Cyg - mag. +1.25). This blue-white luminous supergiant forms the faintest corner of the well-known and much observed "Summer Triangle". The other two stars that make up the triangle are Vega (α Lyr - mag. +0.03) and Altair (α Aqr - mag. +0.77). Once you have located Deneb, move approx. 4.5 degrees east-southeast to ξ Cyg (mag. +3.72) and then hop another 5.5 degrees northeast to ρ Cyg (mag. +3.98). Positioned 3 degrees directly north of this star is M39. The cluster is best seen from northern latitudes during July, August and September.
NGC 7293 is a large and well-known planetary nebula located in the faint zodiac constellation of Aquarius. Also known as Caldwell 63, it's one of the nearest objects of its type and a beautiful example of a remnant of a dying star. It contains a double ring structure, not unlike two coils of a spring; hence the popular name the Helix Nebula.
Although the area of sky surrounding the Helix Nebula is devoid of bright stars, it can be easily located by star-hoping. The nebula lies roughly halfway along an imaginary line connecting Fomalhaut (α PsA - mag. +1.2), the brightest star in the constellation Piscis Austrinus, and ι Aqr (mag. +4.3). Just over a degree east of the Helix is υ Aqr. At magnitude +5.2, this star is faintly visible to the naked eye under dark skies and acts as a good marker.
M57, the Ring Nebula, is a showpiece planetary nebula located in the constellation of Lyra. It's probably the most well-known, studied and photographed object of its kind and a perennial favourite with amateur astronomers. The nebula is relatively bright at magnitude +8.8 and easy to locate. It can be found about 40% the way along an imaginary line connecting stars, Sheliak (β Lyr - mag. +3.5) and Sulafat (γ Lyr - mag. +3.2). For Northern Hemisphere observers, it appears high in the sky during the warm summer months although from southern latitudes it appears much lower down.
M57 was discovered by Antoine Darquier de Pellepoix in January 1779.
The Seated Queen
Cassiopeia is a prominent northern constellation named after Queen Cassiopeia, the wife of King Cepheus of Ethiopia. In Greek mythology, the Queen was arrogant and extremely boastful about her beauty. Legend has it she claimed both her and her daughter, Andromeda, were more beautiful than all the Nereids the nymph-daughters of the sea god Nereus. This brought the wrath of the ruling god of the sea Poseidon who decided to destroy the kingdom.
After consulting a wise oracle, the only way the King and Queen could stop Poseidon from carrying out his threat was to scarify Andromeda. The princess was left helplessly chained to a rock at the sea edge, awaiting her fate at the hands of Cetus, the sea monster. However, just in time, the hero Perseus arrived to save Andromeda and in the process killed the sea monster. Although Andromeda lived to marry Perseus, Poseidon deemed that Cassiopeia should not escape punishment and banished her to the sky forever, tied to the chair of torture!