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Ursa Minor - Constellation Guide
Ursa Minor
Ursa Minoris
UMi
The Little Bear
Introduction
Ursa Minor is a medium size constellation located in the far northern reaches of the sky. Also known as the Little Bear, its main group of stars resemble a smaller version of the Great Bear of Ursa Major. Greek astronomer Thales first mentioned the constellation, around 600 BC, after realising it could be used as a better guide to finding true north than Ursa Major. Over the years it has been visualised as many things, including a dog's tail revolving its tip and a bunch of jewels.
Ursa Minor has been important for navigation since it contains the North Celestial Pole (NCP). Currently, the constellation's brightest star Polaris (mag. +1.97) is only three quarters of a degree from the NCP, thereby providing a convenient marker. Polaris is slowly edging nearer and on March 24, 2100 it will be less than half a degree removed. After that it gradually moves away.
Like Ursa Major, the main seven stars of Ursa Minor form the handle of a ladle. The bowl contains second magnitude Kochab (β UMi) and third magnitude Pherkad (γ UMi), which are collectively known as the guardians of the pole. The remaining members of the group are fainter, down to fifth magnitude, but do provide a useful sky darkness check scale. On good nights all seven stars can be seen with the naked eye.
In terms of size, Ursa Minor covers 256 square degrees and is the 56th largest constellation in the sky. It's devoid of bright deep sky objects but contains a few interesting galaxies within amateur range, including the Ursa Minor Dwarf galaxy, a satellite of the Milky Way. Ursa Minor also contains some variable stars and a few double stars of interest.
From locations north of latitude 25N, the constellation is circumpolar and therefore never sets. For those living south of 25S, it always remains below the horizon and can never be seen.
Ursa Minor Star Chart - pdf format (credit:- freestarcharts)
Aries - Constellation Guide
Aries
Arietis
Ari
The Ram
Introduction
Aries is a medium-sized northern constellation of the zodiac that lies in a rather barren part of the sky. It contains mostly inconspicuous faint stars and is bordered by Taurus to the east, Perseus and Triangulum to the north, Pisces to west and Cetus to the south. The constellation was one of the original 48 constellations plotted by second century astronomer Ptolemy and remains today as one of the modern 88 constellations defined by the IAU (International Astronomical Union).
In Greek mythology, Aries represents the golden ram that was sent to rescue Phrixos and Helle, the children of King Athamus of Boeotia and his first wife Nephele. The King's second wife, Ino, was resentful and wanted the children, in particular, Phrixos killed. She induced a famine in the Kingdom and then falsified a message to the King, indicating Phrixos must be sacrificed in order to save the land. Athamus was about to sacrifice his son, when Aries - sent by Nephele - arrived. The ram managed to rescue Phrixos, but Helle didn't survive. Phrixus then sacrificed the ram to Zeus with its Golden Fleece presented to King Aeëtes of Colchis. In a later myth, Jason and the Argonauts who actively sought the fleece eventually managed to steal it. In ancient Egyptian astronomy, Aries was associated with the god Amon-Ra, who was depicted as a man with a ram's head and represented fertility and creativity. The Arabs knew Aries as a sheep and the Chinese as a dog.
The constellation contains a single second magnitude star, one third magnitude star, three fourth magnitude stars and over a dozen fifth magnitude stars. It contains no Messier objects and no bright deep sky objects. However, its boundaries contain numerous faint galaxies within the range of medium / large size amateur scopes. For small scopes, there are a handful of nice double stars, including some bright ones.
Two thousand or so years ago Aries contained the vernal equinox, the point where the Sun annually passes from south to north across the celestial equator. This occurs on or about March 20th and signals the start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. Due to precession the vernal equinox has now moved into neighbouring Pisces.
Aries covers 441 square degrees of sky, ranking it 39th in overall size. It's best seen from Northern Hemisphere locations during the months of October, November and December. There are several meteor showers that radiate from Aries, including the Daytime Arietids and the Delta Arietids.
Gemini - Constellation Guide
Gemini
Geminorum
Gem
The Twins
Introduction
Gemini is a northern zodiac constellation and one of the 48 constellations described by second century astronomer Ptolemy. Its name is Latin for the twins and it's one of the few constellations in the sky that actually looks like what it suppose to represent. This bright grouping contains two-standout stars, Castor (α Gem) and Pollux (β Gem). At mag. +1.16, Pollux is the brighter while multiple system Castor shines at mag. +1.58. Surprisingly, Pollux was assigned beta Geminorum by Johann Bayer - the German astronomer who labelled the stars with Greek letters in 1603 - even though it easily outshines Castor. Some astronomers have suggested that maybe Pollux has since brightened or Castor faded, but both possibilities seem extremely improbable. The likelihood is that Bayer simply made a mistake and didn't carefully distinguish which was the brighter star.
In Greek mythology, Castor and Pollux were twin brothers whose mother was Queen Leda although Castor was the mortal son of King Tyndareus and Pollux the divine son of Zeus. Together the twins were known as the Dioscuri, which means the sons of Zeus. However, in most versions of the myth only Pollux was Zeus's child. The twins were the patron saints of mariners, appearing in ships rigging as the St Elmo's fire phenomena. When Castor died, Pollux begged Zeus to give Castor immortality, which he did, thereby reuniting the twins together in the heavens forever.
In Babylonian astronomy, the twins were regarded as minor gods. In Chinese astronomy, part of Gemini represented the White Tiger of the West and another part the Vermillion Bird of the South. In more modern times, William Herschel in 1781 discovered Uranus near eta Geminorum (η Gem). In 1930, Clyde Tombaugh discovered Pluto on photographic plates centered on Wasat (δ Gem). Project Gemini was also the name of NASA's second human spaceflight program during the 1960's.
Gemini occupies 514 square degrees of sky and is partly located among the rich star fields of the Milky Way. The constellation is positioned high in the sky for Northern Hemisphere observers during the winter months. It's less well placed from southern locations but nevertheless can still be seen at latitudes as far as 60 degrees south. Deep sky objects within amateur range include some fine open clusters, planetary nebulae, a reflection nebula and a supernova remnant. In addition, there are many nice double stars. Gemini contains only one Messier object, open cluster M35.
The Sun passes through Gemini from late June to late July. The constellation is also the radiant for the Geminids, a rich December meteor shower and highlight of the annual meteor calendar.
NGC 2261 - Hubble's Variable Nebula - Reflection Nebula
NGC 2261 is a curious reflection nebula in Monoceros that's known as Hubble's Variable Nebula. It was discovered by William Herschel in 1783 and is illuminated by variable star R Monocerotis (R Mon). The nebula is unusual in that it changes shape over a period of just days and can vary by up to 2 magnitudes in brightness. The variations are believed to be due to periodic changes in the amount of dust surrounding R Mon, thus affecting the amount of light that reaches us. With an apparent magnitude of +9.0, it can be spotted with binoculars under dark skies.
The variability of R Mon (between magnitudes +10 and +12) was discovered at the Athens Observatory in 1861, but it wasn't until 1916 when Edwin Hubble realised that the nebula also changes in brightness. The variations are such that even on images taken only days apart, structural changes can be seen.
NGC 2261 was chosen as the "first light" photograph on January 26, 1949 for the 200-inch (5.1 m) Hale reflecting telescope under the direction of American astronomer Edwin Powell Hubble. At the time, the newly constructed Hale telescope was the largest telescope in the world and remained so until 1976. NGC 2261 is number 46 in the Caldwell catalogue.
NGC 4755 - Jewel Box - Open Cluster
NGC 4755, also known as the Jewel Box or Kappa Crucis Cluster, is one of the finest open clusters in the sky. It's located in the small southern constellation of Crux and at magnitude +4.2 is bright enough to be seen with the naked eye. It contains over 100 stars, mostly blue or red, spread over 10 arc minutes of apparent sky. This cluster is one of a handful of night time objects that offers something for all observers of all telescope sizes.
NGC 4755 is located 6,440 light-years distant and is best seen from southern latitudes during the months of March, April and May. It's circumpolar from locations south of 30S and can also be seen from the tropics, although for many Northern Hemisphere observers it never rises above the southern horizon.
NGC 891 - Silver Sliver - Unbarred Spiral Galaxy
NGC 891 is a tenth magnitude unbarred spiral galaxy located in Andromeda. Also known as the Silver Sliver, it's one of the best examples of an edge-on galaxy in the sky although a challenging object for small scopes. Due to its attractiveness and scientific appeal, NGC 891 was selected on October 12, 2005 to be the first light image of the Large Binocular Telescope at Mount Graham International Observatory in Arizona. In 2012, it was again selected as first light image, this time for the Discovery Channel Telescope (DCT) Large Monolithic Imager at the Lowell Observatory in Happy Jack, Arizona.
The Silver Sliver was discovered by William Herschel on October 6, 1784 and is best seen from the Northern Hemisphere during October, November and December. Astronomers think our Milky Way galaxy would look remarkably similar, if viewed edge-on.
Finder Chart for NGC 891 - pdf format (credit:- freestarcharts)
The Silver Sliver is located in eastern Andromeda close to the Perseus border. It's positioned 3.5 degrees east of beautiful double star Almach (γ And - mag. +2.1) with naked-eye open cluster M34 (mag. +5.5) a further 3.5 degrees to the east.
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.
Messier 81 - M81 - Bode's Galaxy (Spiral Galaxy)
M81, also known as Bode's galaxy, is a large bright spiral galaxy located 11.8 million light-years away in the constellation of Ursa Major. With an apparent magnitude of +6.9, it's easily visible with binoculars and is a superb target for all sizes of telescopes. This galaxy is a striking example of a grand design spiral and exhibits near perfect and well defined spiral arms.
In the same binocular and low magnification telescope field of view as M81 is another prominent galaxy, M82. At mag. +8.4, M82 is fainter than M81 and a very different type of galaxy. It's a starburst galaxy, in which stars are been formed at exceptionally high rates. Also known as the Cigar galaxy, M82 is the prototype object and provides a striking contrast to the near perfect spiral shape of M81. Together, they form a popular visual and imaging target for amateur astronomers.
Both M81 and M82 were discovered by Johann Elert Bode on December 31, 1774. Pierre Mechain independently rediscovered them in August 1779. He reported his observations to Charles Messier who added them both to his catalogue on February 9, 1781.
Finding M81 is not particularly difficult as the famous Plough asterism of Ursa Major can be used as a starting point. First focus on Dubhe (α UMa - mag. +1.8), the northwest corner star of the bowl. The M81 / M82 pair is located 10 degrees to the northwest of this star with M82 positioned 38 arc minutes directly north of M81.
Messier 31 - M31 - Andromeda Galaxy (Spiral Galaxy)
M31, the famous Andromeda Galaxy, is the largest member of the Local Group that also includes the Milky Way, the Triangulum Galaxy (M33) and about 50 other smaller galaxies. With an apparent mag. of +3.4, it's one of the brightest Messier objects and easily visible to the naked eye even from areas with a certain amount of light pollution. M31 is usually regarded as the most distant object that can be easily seen without optical aid.
The Andromeda Galaxy has been known for a long time. It was first recorded over 1000 years ago by Isfahan based Persian astronomer Abd-al-Rahman Al-Sufi. In 964 AD, he described it as the little cloud in his Book of Fixed Stars. This object was almost certainly known - for a number of years before this date - to other Persian astronomers. The first person to telescopically observe and describe M31, was German astronomer Simon Marius on December 15, 1612. Unaware of both Al Sufi's and Marius' discovery, Giovanni Batista Hodierna independently rediscovered the object sometime before 1654. Then on August 3, 1764, Charles Messier added the great spiral to his catalogue. Incidentally, Messier incorrectly credited Marius as the discoverer, apparently unaware of the earlier work of Al-Sufi.
For a long time, the true nature of M31 was unknown. It was simply regarded as a large nebula located within our galaxy. Up until the 20th century, it was referred to as either the Andromeda Nebula or the Great Andromeda Nebula. In the 18th century, William Herschel incorrectly believed M31 was one of the nearest nebulae, located at a distance of not more than 17,000 light-years. However, he was correct in viewing the galaxy as an island universe like the Milky Way, although at such a small distance it would be much smaller in size than our own galaxy.
