Messier 2 - M2 - Globular Cluster

M2 is a rich compact globular cluster at the edge of naked eye visibility that's located in the constellation of Aquarius. It's an easy binocular object (mag. +6.3) but requires a dark site with extremely good seeing conditions to be spotted with the naked eye.

M2 was discovered on September 11, 1746 by French astronomer Jean-Dominique Maraldi while observing a comet with Jacques Cassini, the son of legendary Italian astronomer Giovanni Cassini. Charles Messier then rediscovered it exactly 14 years later. He described the cluster, like many of his other objects, as "a nebula without any stars associated with it". William Herschel was the first to resolve individual stars in 1783.

Finding M2 can be initially challenging as it's located in a relatively sparsely populated area of sky. The key is to locate the two brightest stars in Aquarius, Sadalsuud (β Aqr - mag. +2.90) and Sadalmelik (α Aqr - mag. +2.95). Sadalsuud is positioned 10 degrees southwest of Sadalmelik and located 5 degrees north of Sadalsuud is M2. Together the two stars and the globular cluster form a large right-angled triangle.

M2 straddles the celestial equator and is therefore visible from all over the World, although it appears higher in the sky when viewed from tropical latitudes. It's best seen between July and October.

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Capella - Alpha Aurigae - α Aur

Capella is a bright yellow star located in the northern section of sky. With an apparent magnitude of +0.08, it's marginally fainter than another bright northern star, Vega. Capella is the standout star of the relatively large constellation of Auriga, the Charioteer. The Milky Way passes through the heart of Auriga and as a result it contains numerous bright open clusters, nebulae and interesting stars.

Capella is the northernmost first magnitude star and is circumpolar from latitudes greater than +44 degrees. The star can still be spotted from most southerly regions including Australia, New Zealand and Argentina. However, it's not visible from the Falkland Islands or Antarctica.

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Algol eclipse dates and times for October 2017

Algol (β Per) is a bright eclipsing binary system located in the northern constellation of Perseus and one of the best-known variable stars in the sky. Often referred to as the "Demon Star", most of the time it shines at mag. +2.1 but every two days, 20 hours and 49 minutes it suddenly dips in brightness to mag. +3.4, remaining dim for about 10 hours before returning to its original state.

Why the change in brightness? The Algol system consists of at least three-stars (β Per A, β Per B and β Per C) with the orbital plane of Algol A and B directly in line with the Earth. The regular dips in brightness occur when the dimmer B star moves in front of and eclipses the brighter A star. There is also an extra dimension in that a secondary eclipse occurs when the brighter star occults the fainter secondary, resulting in a very small dip in brightness that can be detected with photo-electrical equipment.

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NGC 869 and NGC 884 - The Double Cluster - Open Clusters

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.

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Messier 76 - M76 - The Little Dumbbell Nebula (Planetary Nebula)

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.

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NGC 6541 - Globular Cluster

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.

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NGC 752 - Open Cluster

NGC 752 is a large spawling open cluster in the constellation of Andromeda. With an apparent magnitude of +5.7, it's visible to the naked eye from a dark site appearing as a large unresolved fuzzy patch of light. The cluster is one of the finest large open clusters in the sky and contains over 70 stars spread across a huge 1.25 degrees of apparent sky. Due to its size, NGC 752 is best observed with binoculars or through wide field telescopes at low powers.

NGC 752 is located 5 degrees south and slightly west of outstanding double star Almach (γ And - mag. +2.1) the third brightest star in the constellation. It was discovered by Caroline Herschel on September 29, 1783 although it was probably observed sometime before 1654 by Italian astronomer Giovanni Battista Hodierna. Caroline's brother William Herschel subsequently added it to his catalogue a couple of years later. It's best seen from northern latitudes during the months of October, November and December. The cluster is number 28 in the Caldwell catalogue.

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Almach - Gamma Andromedae - γ And - Double Star

Almach (γ And) is one of the finest double stars in the sky. To the naked eye, it appears as a single bright star of magnitude +2.10, but small scopes reveal an outstanding double, made up of a bright yellow or slightly orange primary and a fainter deep blue secondary. It's widely regarded as the second best colour contrast double in the sky, surpassed only by Albireo in Cygnus.

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NGC 457 - Owl Cluster - Open Cluster

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.

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