Guides / Star Charts
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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.
Messier 45 - M45 - The Pleiades (Open Cluster)
M45, commonly known as the Pleiades or Seven Sisters, is the finest open cluster in the sky. It's a breathtaking site, known since antiquity and easily visible to the naked eye. Located in the large and prominent zodiac constellation of Taurus, this showpiece object is best seen during the Northern Hemisphere Winter and the Southern Hemisphere Summer months.
Finding M45 is easy. The cluster is positioned about 14 degrees northwest of orange giant star Aldebaran (mag. +0.9), the brightest star in Taurus. At first glance with the naked eye, it's obvious that something is special about this small section of sky. On closer inspection, M45 reveals itself to be a beautiful cluster of about half a dozen white stars, covering an area much greater than that of the full Moon. At the heart of the cluster is a set of stars that form a small dipper shape, similar to the brightest stars of Ursa Major. Even under light polluted skies the dipper shape is readily visible. From dark sites, the Pleiades is an outstanding naked eye object. The main stars appear bright and striking, with up to 10 or more visible under ideal conditions.
The Planets this Month - November 2018
Mercury
Mercury reaches greatest elongation east (GEE) on November 6th when it's 23 degrees in the sky from the Sun. From equatorial and southern locations, the inner planet can be found low down in the western evening sky early in the month just after sunset. It will set up to two hours after the Sun on the day of GEE and shine at magnitude -0.3. Each subsequent evening, the planet's visibility slightly decreases until it's eventually lost to the bright twilight. Mercury reaches inferior conjunction on November 27th.
From mid-latitude northern locations, the shallow angle of the ecliptic to the horizon means it will be a difficult low down target, best seen around GEE.
Venus
Venus returns to the morning sky this month. The brilliant planet is unmistakable before sunrise above the eastern horizon. As the month progresses it climbs higher in the sky, with its brightness increasing from magnitude -4.6 to -4.9 as the month progresses. Its angular size decreases from 60 to 41 arc seconds this month with its illuminated phase increasing from only 1% to 25%.
Mars
Mars is now an evening object. The 'Red planet' starts November in Capricornus before crossing into Aquarius on the 12th where it remains for the rest of November. Mars continues to fade with its magnitude decreasing from -0.6 to -0.1 as the month progresses. From southern locations, it appears high in the north-western sky after sunset. From northern locations, Mars can be seen in the southern sky and improves in elevation each subsequent evening.
The angular size of the planet decreases from 11.9 arc seconds to 9.3 arc seconds during the month. However, this is still large enough to spot major features, such as Syrtis Major, on its pink surface. The waxing gibbous Moon passes a degree south of Mars on November 16th.
Mars during November 2018 - pdf format (credit:- freestarcharts)
Algol eclipse dates and times for November 2018
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 35 - M35 - Open Cluster
M35 is a fantastic open cluster located in the constellation of Gemini. At magnitude +5.2, it's visible to the naked eye under good conditions. Curiously, despite being a naked eye object, it wasn't discovered until 1745-46 by Philippe Loys de Chéseaux and then independently "re-discovered" by John Bevis sometime before 1750. Since the cluster is reasonable close at 2,800 light-years it presents a large apparent diameter of some 28 arc minutes - almost exactly the same as that of the full Moon. Without a doubt, M35 is a magnificent sight in all types of optical instruments.
The constellation Gemini covers a reasonable 514 sq. degrees and is partially located in the rich star fields of the Milky Way. During the winter months, it's positioned high in the sky for Northern Hemisphere observers although less well placed for those located further south. Surprisingly, despite such a prime Milky Way location, M35 is the only Messier object in Gemini. It's located at the western edge of the constellation in a corner of the sky close to the Taurus, Orion and Auriga borders. Finding M35 is quite easy as it's 3.5 degrees northwest of mag. +2.9 star, Mu (μ) Gem.
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)
The Planets this Month - October 2018
Mercury
Mercury is an early evening object during the second half of October from southern and tropical latitudes. The fast moving planet can be seen low above the western horizon just after sunset. During the visibility period its brightness hardly changes at about magnitude -0.2. By month's end, from mid-latitude southern locations, Mercury sets 1 hour and 45 minutes after the Sun. From mid-latitude northern locations, the planet is not so well placed, but might just be spotted very low in the west towards the tail end of the month.
On October 14th, Mercury (mag. -0.3) passes 7 degrees north of much brighter Venus (mag. -4.5) and on October 30th, Mercury passes 3 degrees south of Jupiter (mag. -1.7).
Venus
Venus is an early evening object visible during the first half of the month from southern and equatorial latitudes. However, the planet will move closer to the Sun with each passing day. Observers at mid-latitude northern locations will struggle to spot Venus at all this month.
As previously mentioned on October 14th, Venus and Mercury are located in the same region of sky. Venus reaches inferior conjunction on October 25th.
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.
Algol eclipse dates and times for October 2018
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.