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Messier Catalogue
The Messier Catalogue is a famous catalogue in Astronomy. It consists of 110 deep sky objects, including open and globular star clusters, galaxies, nebulae, an asterism, a double star and even a supernova remnant. It was compiled in the 18th century by Charles Messier.
Messier was a comet hunter who was born in Badonviller, France on June 26, 1730. When searching for comets he was frustrated by fixed objects that looked like comets in the night sky but actually weren't. These fuzzy "comet" like objects hindered his searches so he catalogued them in order to avoid them in future.
The first version of his catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris. Over the next 7 years he updated the catalogue and published the final version in 1781, containing 103 objects. Many of these objects he actually discovered himself.
On several different occasions between 1921 and 1966, astronomers and historians discovered evidence of another 7 deep-sky objects that were observed either by Messier or his friend and assistant, Pierre Mechain, shortly after the final version was published. These objects, numbered M104 to M110, are now accepted by astronomers as "official" Messier objects.
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.
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.
Messier 41 - M41 - Open Cluster
M41 is a stunning, large bright open cluster located in the constellation of Canis Major. Of the many clusters in Canis Major, it's the stand out object and the constellation's only
M41 was discovered by Giovanni Batista Hodierna sometime before 1654, although it was probably known to Aristotle as far back as 325 BC. If true, this would make it the faintest object recorded in classical antiquity, but caution prevails as Aristotle may have described a nearby part of the Milky Way instead. The cluster was catalogued by Charles Messier on January 16, 1765 and is best seen during the months of December, January and February from the tropics and Southern Hemisphere.
Finder Chart for M41 - pdf format (credit:- freestarcharts)
Algol eclipse dates and times for January 2020
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.
Ursa Major - Constellation Guide
Ursa Major
Ursa Majoris
UMa
The Great Bear
Introduction
Ursa Major or the Great Bear is a prominent constellation in the northern celestial hemisphere. It's the third largest constellation in the sky and contains a central feature of seven stars, known as the Plough or Big Dipper, which is one of the most recognisable patterns. It's made up of stars, Dubhe, Merak, Phecda, Megrez, Alioth, Mizar and Alkaid. Ursa Major was listed by Ptolemy as one his 48 constellations in his second century Almagest and remains today as one of the modern 88 constellations.
The constellation spans a vast swath of the northern sky, covering almost 1,280 square degrees in surface area. Of course, the Plough is its standout feature, which has been referenced in drawings and writings since the dawn of civilisation. In Europe, the pattern symbolised a wagon or chariot that was associated with King Arthur. In Roman mythology, Jupiter the King of the God's, lusted after a beautiful woman named Callisto who was transformed into a bear by his jealous wife, Juno. Arcas the son of Callisto almost shoots the bear, but to avoid tragedy, Jupiter turns Arcas also into a bear, placing them both in the sky as Ursa Major and Ursa Minor. The Arabs viewed the grouping as a coffin and Ursa Major, along with Orion and the Pleiades, are mentioned in the Bible.
Most of the stars of the Plough belong to a nearby stellar group, known as the Ursa Major Moving Group or Collinder 285. All member stars are moving in roughly the same direction and at about 80 light-years distant it's the nearest cluster like object to Earth. Of the seven stars, only Dubhe and Alkaid are not actual group members.
The Plough asterism is a very useful guide for locating other stars. Two stars in the bowl Dubhe and Merak act as a pointer to Polaris, the Pole star. An imaginary line extending from Megrez through Dubhe and onwards leads to first magnitude Capella. The handle of the Plough points towards the brightest star in the northern section of the sky Arcturus.
Ursa Major is circumpolar from many Northern Hemisphere locations and is best seen during the months of March, April and May.
Ursa Major Star Chart - pdf format (credit:- freestarcharts)
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)
47 Tucanae - NGC 104 - Globular Cluster
47 Tucanae or 47 Tuc is a spectacular globular cluster located in the southern constellation of Tucana. At magnitude +4.5, it appears to the naked eye as a slightly fuzzy star similar to the head of a tail-less comet. Always hidden from view for European and North American observers, 47 Tuc was discovered by French astronomer Nicolas Louis de Lacaille on September 14, 1751. Initially Lacaille though he had found a comet until further inspection revealed its true nature.
47 Tuc is the second brightest globular in the sky, only Omega Centauri is more brilliant. It has an extremely dense core and is one of the most massive globular clusters surrounding the Milky Way. The cluster is located 2.5 degrees west of the Small Magellanic Cloud (SMC) and from most of the Southern Hemisphere it's circumpolar and never sets. In contrast from latitudes of 18N or greater, the globular can never be seen as it fails to rise above the horizon.
Through 7x50 or 10x50 binoculars, 47 Tuc appears as a bright starlight nucleus surrounding by a halo of soft pearly light. It's clearly non-stellar in nature. Telescopically the cluster is stunning and a showpiece object of the night sky. It total it spans 31 arc minutes of apparent sky, almost exactly the same diameter as the full Moon. For comparison, 47 Tuc is 50% larger and 3x brighter than M13 "the Great Hercules Globular Cluster" widely regarded as the finest globular in the northern section of the sky.
A small 100mm (4-inch) scope reveals a bright compact core surrounded by a large 15 arc minute sphere with the brightest members resolvable. Even through small telescopes it's a superb sight. A 200mm (8-inch) instrument shows a swarm of stars in a glittering 3D view. The dense centre remains unresolvable in stark contrast to the less dense outer regions. Overall it's a breathtaking object for all sizes and types of telescopes.
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.
Finder Chart for NGC 457 - pdf format (credit:- freestarcharts)