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Hercules - Constellation Guide
Hercules
Herculis
Her
The Strongman
Introduction
The constellation of Hercules is one of the original 48 constellations plotted by 2nd century astronomer Ptolemy and remains today as one of the modern 88 constellations. Hercules is the 5th largest constellation and spans an impressive 1,225 square degrees of sky. However, despite its large apparent size it's rather faint. Although easily traceable under dark skies, the constellation can become elusive with just a hint of light pollution or when viewed under a moonlit sky.
The centrepiece of Hercules is a trapezoid shaped asterism commonly known as the Keystone. The four stars of the Keystone are Eta Herculis, Zeta Herculis, Epsilon Herculis and Pi Herculis. They are all between magnitudes 3 and 4 in brightness. The brightest of the four, Zeta Herculis, shines at magnitude + 2.81 and is the second brightest star in the constellation. Along with marginally brighter Kornephoros (Beta Herculis) these are the only two stars in Hercules above magnitude +3.0.
For deep sky enthusiasts Hercules contains a sprinkle of globular clusters, challenging planetary nebulae and a host of faint galaxies.
Algol eclipse dates and times for June 2022
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 brightness change. 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.
Messier 44 - M44 - The Praesepe (Open Cluster)
M44, also known as the Praesepe or Beehive cluster, is a sprawling open cluster. It's the brightest and most prominent deep sky object in the constellation of Cancer. Visible to the naked eye under dark skies, the cluster appears like a large misty cloud covering over 1.5 degrees of sky. The brightness and size of M44 results from its close proximity to Earth; it lies a mere 577 light-years distant. Only the Hyades (at 153 light-years), Coma cluster (280 light-years), the Pleiades (M45) (425 light-years), Southern Pleiades (480 light-years) and IC 2391 (500 light-years) are nearer. Consequently, M44 is one of the brightest and largest objects of its type in the night sky.
The constellation of Cancer is a faint zodiac constellation that's bordered by much brighter Leo to the east and Gemini to the west. To the north is faint Lynx, with Canis Minor and Hydra located on the southern side. At the heart of Cancer is a grouping of four faint stars. They are Asellus Australis (δ Cnc - mag. +3.9), Asellus Borealis (γ Cnc - mag. +4.7), η Cnc (mag. +5.3) and θ Cnc (mag. +5.3). Of these, the brighter two are relatively easy naked eye objects, the fainter ones more difficult. Positioned at the centre of this grouping is M44. An alternative method of locating M44 is to imagine a line extending in a southeastern direction from Pollux (β Gem - mag. +1.1) for 37 degrees to Regulus (α Leo - mag. +1.4). M44 is positioned approximately at the mid-point of this line.
Algol eclipse dates and times for July 2022
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 brightness change. 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.
Messier 57 - M57 - The Ring Nebula (Planetary Nebula)
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.
Messier 13 - M13 - Great Hercules Globular Cluster
M13 is a spectacular globular cluster and the best example of its type in the northern section of sky. It's the standout deep sky object in the constellation of Hercules and is sometimes referred to as the Great Hercules Globular Cluster. At mag. +5.8, it's just about visible to the naked eye and an easy binocular target. The popularity of M13 is mainly due to its declination; it lies at 36N and from northern temperate latitudes is well placed high in the sky during summer months. There are many other globulars larger and brighter than M13, but all are located in the southern section of the sky. As a result, they either never rise or appear low down from most North America, European and Asian locations. Hence, M13 is perhaps the most observed and studied globular cluster of all.
M13 was discovered by the Astronomer Royal, Sir Edmond Halley in 1714. He described it as "a little patch, but shews itself to the naked eye, when the sky is serene and the Moon is absent". Fifty years later, Charles Messier catalogued it on June 1, 1764.
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.
Finder Chart for NGC 869 and NGC 884 The Double Cluster - pdf format (credit:- freestarcharts)
Messier 67 - M67 - Open Cluster
Messier 67 is a very old open cluster located in the constellation of Cancer. Estimations of its age vary between 3.2 and 5 billion years, with recent valuations putting it at 4 billion. This makes it one of the oldest known open clusters. As a consequence, M67 contains a variety of stellar types including many Sun like stars, red giants and white dwarfs. It's easily the most ancient Messier open cluster. For comparison, the Praesepe (M44) is 600 million years old and the brilliant Pleiades (M45) a very youthful 100 million years.
The constellation of Cancer is a faint zodiac constellation that's bordered by much brighter Leo to the east and Gemini to the west. To the north lies Lynx, with Canis Minor and Hydra positioned on the southern side. To find M67, first locate stars Asellus Australis (δ Cnc - mag. +3.9), Asellus Borealis (γ Cnc - mag. +4.7), η Cnc (mag. +5.3) and θ Cnc (mag. +5.3). This quadrangle forms the main part of the constellation and located at its centre is M44. Next focus on another faint star, α Cnc (mag. +4.3), which is positioned 9 degrees further to the southeast. M67 is positioned 1.75 degrees west of this star.
M67 was discovered sometime before 1779 by German astronomer Johann Gottfried Koehler. He described it as being rather conspicuous and nebula like, although with his basic telescope he was unable to resolve any stars. Charles Messier then independently rediscovered M67, resolved it into stars and catalogued it on April 6, 1780. He noted it as a "cluster of small stars with nebulosity, below the southern claw of Cancer. The position determined from the star Alpha [Cancri].".
M67 is best seen from the Northern Hemisphere during the months of February, March and April.
Algol eclipse dates and times for May 2022
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 brightness change. 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.