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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 May 2023
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.
Algol eclipse dates and times for June 2023
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.
Vulpecula - Constellation Guide
Vulpecula
Vulpeculae
Vul
The Fox / The Little Fox
Introduction
Vulpecula is a small, faint constellation located in the northern section of the sky. Strangely, it was not one of the original 48 constellations created by 2nd century astronomer Ptolemy, even though the pattern of stars were clearly visible to him and other ancient Greeks and Romans.
The constellation we know today was created by Johannes Hevelius. He included it in his influential 56 page star atlas, Firmamentum Sobiescianum, which was published posthumously in 1690. Originally it was known by two names, Vulpecula cum anser and Vulpecula et Anser. The first means the little fox with the goose and the second the little fox and the goose. In his original illustration, Hevelius depicted an unfortunate goose carried in the jaws of a fox. Later the constellation was divided into two separate parts, Vulpecula and Anser. It was then re-merged into a single entity - simply named Vulpecula - by the International Astronomical Union (IAU) in the 20th century. The only remains of the goose is the constellation's brightest star, Anser (α Vul).
Locating the area of the sky where Vulpecula lies is easy; it's wedged between Cygnus and Sagitta with the western half located roughly in the middle of the well observed Summer triangle (an asterism consisting of the bright stars Deneb, Vega and Altair). For deep sky observers, Vulpecula contains the superb Dumbbell Nebula, a famous coathanger shaped open cluster and a few other open clusters. At 288 square degrees, it's the 55th largest constellation in the sky.
Crux - Constellation Guide
Crux
Crucis
Cru
The Southern Cross
Introduction
Despite having the smallest size of all constellations - a mere 68 square degrees - Crux is the most celebrated of all southern constellations. Its name is Latin for cross, which refers to the main asterism of the four relatively bright stars at its centre. To some the cross shape is more resembling of a kite, but whatever you think it looks like it's superb and unmistakable.
Positioned in the sky at a declination of about -60 degrees, Crux is visible from all parts of the Southern Hemisphere and for many of these observers it's circumpolar. For residents just north of the equator the cross can be spotted during late spring, low down above the southern horizon. Unfortunately, for most Northern Hemisphere observers this superb constellation never manages to climb above the horizon and can never be seen.
NGC 5139 - Omega Centauri - Globular Cluster
Omega Centauri (NGC 5139) is the brightest and most spectacular globular cluster in the sky. Located in Centaurus and visible to the naked eye (mag. +3.7) it was believed by early astronomers to be star. In AD 140, Greek mathematician and astronomer Ptolemy included it in the "Almagest" his star catalogue. Using Ptolemy's data, Johann Bayer a German lawyer and uranographer (celestial cartographer) designated the "star" as Omega Centauri in his publication Uranometria (1603). It was Edmond Halley, in 1677, who first identified its non-stellar nature.
The cluster is best seen from southern locations during the months of March, April and May. From latitudes north of 42N it never rises above the horizon and can't be seen at all. It's listed as number 80 in the Caldwell catalogue.
The globular is positioned close to the middle of Centaurus. Located 5 degrees east of Omega is zeta Centauri (ζ Cen - mag. +2.6). About 15 degrees southeast of the globular are first magnitude stars Alpha and Beta Centauri and about the same distance on the southwestern side is the famous constellation of Crux, the Southern Cross.
18 Scorpii - The nearest Solar twin
Most of the stars visible to the naked eye in the night sky are much larger, more luminous and brilliant than the Sun. However, despite often labelled as an average star the Sun actually outshines most stars in the galaxy. It's believed up to 80% of all stars in the Milky Way are red dwarfs. This type of star is so dim that not one is bright enough to be seen from Earth with the naked eye. Even Proxima Centauri, the closest star to the Earth after the Sun, requires optical aid to be seen. When it comes to solar twins or stars that are incredibly similar to the Sun across all parameters, not many exist. One of the best examples is 18 Scorpii.
Albireo - Beta Cygni - β Cyg - Double Star
Albireo is a showpiece double star and one of the great small telescope objects. To the naked eye, it's the fifth brightest star in Cygnus (combined mag. +2.9) and the lone star that marks the head of "the Swan" constellation. When viewed through small scopes - or even good 10x50 binoculars - it splits into two components. The primary shines at mag. +3.1 (Albireo A) and the secondary at mag. +5.1 (Albireo B). The stars are separated by a generous 34.3 arc seconds, but what makes this special is the vivid colour contrast between the two components. A brilliant yellow primary, accompanied by a soft blue secondary.
Messier 92 - M92 - Globular Cluster
M92, mag. +6.4, is a bright globular cluster located in the northern part of the constellation of Hercules. Despite being almost visible to the naked eye, it's often overlooked due to its close proximity to more spectacular, M13.
M92 is one of the original discoveries of Johann Elert Bode who found it on December 27, 1777. He described it as "a nebula that's more or less round with a pale glow". Charles Messier independently rediscovered it and catalogued it on March 18, 1781. Incidentally, this proved to be Messier's most productive night, during which he discovered another 8 objects all of them Virgo Cluster galaxies (M84 to M91). As with many globulars, it was William Herschel who first resolved it into stars. To date, only about 16 variables have been discovered in M92 of which 14 are of the RR Lyrae type, and one is a rare globular eclipsing W Ursae Majoris type binary.
