Guides / Star Charts
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Sirius - Alpha Canis Majoris - α CMa
There are at least 6,000 stars bright enough to be visible with the naked eye. Under dark skies, up to about 3,000 can be seen at any one time (since one half of the Earth is in daylight). However, none can rival the brilliance of Sirius, the brightest night time star.
Located in the constellation of Canis Major, Sirius shines with an apparent magnitude of -1.46. It's noticeably brighter than its nearest rival Canopus (α Car mag. -0.72) and four times more brilliant than Arcturus, the brightest star in the northern section of sky. Sirius is also known as the "Dog Star". When close to the horizon it twinkles. Of course, the colour variations are only a result of the Earth's unsteady atmosphere. In practice, all stars do twinkle and to a lesser extent the planets as well.
To the naked eye Sirius appears as a single star, but it's actually a binary system. The primary component is a white main sequence star of spectral type, A1V, named Sirius A. This star is the one visible to the naked eye. It has a radius of 1.7 times that of the Sun and is 25 times more luminous.
Messier 42 - M42 - The Great Orion Nebula (Emission/Reflection)
M42, also known as the Great Orion Nebula or Orion Nebula, is the prime deep sky attraction in the constellation of Orion and a showpiece deep sky object. With an apparent magnitude of +4.0, it's easily visible to the naked eye. This emission / reflection nebula and star forming region spans more than a degree of sky and is therefore one of the largest and brightest objects of its type.
Orion is a prominent constellation and one of the most recognizable and familiar sights. Located on the celestial equator, it's visible throughout the World and best seen during the months of December, January and February. The constellation is filled with bright stars, including first magnitude Rigel and Betelgeuse plus a further five second magnitude stars. Three of the second magnitude stars (Mintaka, Alnilam and Alnitak) form the famous belt of Orion. Positioned just 5 degrees south of the belt is the Orion Nebula itself, which is part of the Hunters Sword.
Orion - Constellation Guide
Orion
Orionis
Ori
The Hunter
Introduction
Orion is a prominent constellation that's one of the brightest and most familiar sights in the night sky. Straddling the celestial equator it can be seen from all locations on Earth. Named after a great hunter in Greek mythology, it contains two first magnitude stars, many other bright stars, a famous belt, spectacular nebulae, some impressive multiple stars and fine open clusters. Its most famous inhabitant, the Orion Nebula, is one of the most spectacular deep sky objects in the sky.
The distinctive pattern of Orion has been used historically and in the modern World extensively. The earliest linking is an ivory carving found in a cave in the Ach valley in Germany, which is estimated to be at least 32,000 years old. In Greek mythology, Orion was a handsome strong hunter, born to Euryale the daughter of King Minos of Crete and Poseidon, the god of the sea. Many myths surround the character particularly involving his death. Various versions exist, but generally Orion brought the wrath of goddess Artemis who sent the scorpion to kill him. The resulting outcome is that the hunter and the scorpion are placed on opposite sides of the sky. When Scorpius rises in the east, Orion is setting in the west.
In medieval Muslim astronomy, Orion was known as al-jabbar, the giant. In old Hungarian tradition, Orion was a magic Archer or Reaper and in China the constellation was one of the 28 lunar mansions that reflect the movement of the Moon. The Egyptians associated Orion with Osiris, the god of death, afterlife, resurrection, regeneration and rebirth. They also aligned part of the Great Pyramid of Giza with Alnitak, one of the stars of the belt. For the Aztecs, Orion rising in the east signaled the time to perform the "New Fire" ceremony, a ritual designed to postpone the end of the World. More recently, the film company Orion Pictures used the constellation's main shape as its logo.
Orion is best seen during the months of December, January and February.
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.