Pedro Castle, 3rd July 2011 7.30

The constellation illustrated above, Virgo, is high in the south at the meeting time.
Though a large constellation, Virgo, the Virgin, does not have much of any prominent stellar pattern, relying on Spica to tell us where it is. Also shining brightly in the faint asterism is the planet Saturn, which is very close to Porrima at the moment.
With 26 known exoplanets orbiting around 20 stars in this constellation, Virgo has more confirmed exoplanets than any other constellation. 8 planets in this constellation were discovered in 2009, which is the most planets discovered in a single constellation in a single year.
The star 70 Virginis has one of the first known extrasolar planetary systems with one confirmed planet 7.5 times the mass of Jupiter. Chi Virginis has one of the most massive planets ever detected, at a mass of 11.1 times that of Jupiter. The sun-like star 61 Virginis has three planets: one is a super-Earth and two are Neptune-mass planets.
Because of the presence of a galaxy cluster (consequently called the Virgo cluster) within its borders 5° to 10° west of Vindemiatrix (which can be seen at the “top” on the cart above) this constellation is especially rich in galaxies.
A noted galaxy that is not part of the cluster is the Sombrero Galaxy (M104), an unusual spiral galaxy. It is located about 10° due west of Spica
Though at a distance of 250 light years Spica is still first magnitude (1.04), showing its absolute brilliance, the star visually 1900 times more luminous than the Sun. The apparent brightness is deceptive, however, as Spica actually consists of two stars very close together (a mere 0.12 Astronomical Units apart) that orbit each other in slightly elliptical paths with a period of only 4.0145 four days, which makes them difficult to study individually. Both are blue class B (B1 and B4) hydrogen-fusing dwarfs (the brighter nearing the end of its stable lifetime), making Spica one of the hottest of the first magnitude stars. The high temperature produces a great deal of radiation in the ultraviolet, which renders Spica vastly brighter than visually indicated.
The brighter primary star has a temperature 22,400 Kelvin, a true luminosity of 12,100 Suns, a radius 7 solar, and a mass 10.5 times solar, which may be enough to send it someday into a supernova explosion.
Just up and to the right of Spica lies dimmer, third magnitude Porrima, Virgo's Gamma star (or Gamma Virginis). Unlike most star names, which are Arabic, this one is Latin and honors a Roman goddess of prophecy. A telescope shows a remarkable sight, one of the finest double stars in the sky. The components are almost perfect identical twins, both white class F (F0) dwarf stars with surface temperatures of about 7100 degrees Kelvin, significantly warmer than the Sun. They orbit each other on highly elliptical paths in only 169 years. Thirty-eight light years away, the stars average 43 Astronomical Units from each other, about the distance between the Sun and Pluto, the orbital eccentricity taking them between 81 and 5 AU.
The best Saturn viewing window is nearing its end, just as the ring tilt begins to widen. Saturn moves away from Porrima, and on July 3, it will look more three dimensional as the shadows of the rings and the globe are visible.

Pedro Castle, 4th June 2011, 7.30 p.m.

The meeting this month celebrates the 20th year of the society's existance.
The constellation illustrated above is a constant source of interest to anyone who looks up and is living here, so here is a compendium of what I have found out about it trawling the web.
Crux is visible from latitudes south of 25 degrees North and completely invisible in latitudes above 35 degrees North. Crux, being Latin for cross, is commonly known as the Southern Cross (in contrast to the Northern Cross), and is the smallest of the 88 modern constellations, but nevertheless one of the most distinctive. It is surrounded on three sides by the constellation Centaurus.
The invention of Crux is generally attributed to Royer in 1679, but we know it was written about some two centuries earlier than that. It was defined as a separate asterism in the 16th century after Amerigo Vespucci's expedition to South America in 1501. Vespucci mapped the two stars, Alpha Centauri and Beta Centauri as well as the stars of the Crux.
With the lack of a significant pole star in the southern sky (Sigma Octantis is closest to the pole, but is so faint as to be useless for the purpose), two of the stars of Crux (Alpha and Gamma, Acrux and Gacrux respectively) are commonly used to mark south.
Following the line defined by the two stars for approximately 4.5 times the distance between them leads to a point close to the Southern Celestial Pole.
The Coalsack Dark Nebula (or simply the Coalsack) is the most prominent dark nebula in the skies, easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way.
A dark nebula is a type of interstellar cloud that is so dense that it obscures the light from the background emission or reflection nebula (e.g., the Horsehead Nebula) or that it blocks out background stars (e.g., the Coalsack Nebula). The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. Like other interstellar dust/material, things it obscures are only visible using radio waves in radio astronomy or infrared in infrared astronomy.
The Jewel Box is an open cluster in the constellation of Crux. This famous group of young bright stars was named the Jewel Box from its description by Sir John Herschel as "a casket of variously coloured precious stones," which refers to its appearance in the telescope.
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. They are loosely bound to each other by mutual gravitational attraction and become disrupted by close encounters with other clusters and clouds of gas as they orbit the galactic center resulting in a migration to the main body of the galaxy, as well as a loss of cluster members through internal close encounters.[1] Open clusters generally survive for a few hundred million years. In contrast, the more massive globular clusters of stars exert a stronger gravitational attraction on their members, and can survive for many billions of years. Open clusters have been found only in spiral and irregular galaxies, in which active star formation is occurring.

Pedro Castle, May 6th 2011 7.30 p.m.

High in the north this month lies the small constellation of Canes Venatici.
The Polish astronomer Johannes Hevelius formed this constellation in 1687 from a scattering of faint stars beneath the tail of Ursa Major. Canes Venatici represents two dogs held on a lead by Boötes, snapping at the heels of the Great Bear. The southern dog contains the two brightest stars in the constellation, Alpha and Beta Canum Venaticorum. Ptolemy had listed both these stars in the Almagest as among the “unformed” stars outside the figure of the Great Bear, and hence not belonging to any particular constellation.
The idea of dogs being held by Boötes was not original to Hevelius. On a star chart published in 1533 the German astronomer Peter Apian showed Boötes with two dogs at his heels and holding their leash in his right hand. On another chart published by Apian three years later the number of dogs had grown to three and the leash had moved to the left hand, but the dogs were still following Boötes and not the bear. In neither case was any attempt made to connect the dogs with charted stars, nor were they named, so the credit for showing the dogs in their current position and for making them a separate constellation remains with Hevelius.
The Alpha star is known as Cor Caroli, meaning Charles’s Heart, in honour of King Charles I of England. It was given this title by Sir Charles Scarborough, physician to King Charles II. Scarborough said that the star shone particularly brightly on the night of 1660 May 29, when King Charles II returned to London at the Restoration of the Monarchy. Because of this there has been much confusion over which King Charles the star is supposed to commemorate, but it definitely refers to the first King Charles. It was originally shown in 1673 on a star map by the English cartographer Francis Lamb under the name Cor Caroli Regis Martyris, a reference to the fact that King Charles I was beheaded. Lamb and others, such as the Englishman Edward Sherburne in 1675, drew a heart around the star surmounted by a crown, turning it into a mini-constellation.
The Beta star is called Chara, from the Greek for ‘joy’, the name given by Hevelius to the southern dog. The northern dog, called Asterion (‘little star’), is marked only by a scattering of faint stars. Johann Bode drew the dogs with their names engraved on their collars in his Uranographia atlas.
Canes Venatici contains a globular cluster of stars, M3, and a beautiful spiral galaxy, M51, called the Whirlpool. M51 was the first galaxy in which spiral form was noticed, by the Irish astronomer Lord Rosse in 1845. It consists of a large galaxy in near-collision with a smaller one.

Pedro Castle, 6th April 2011,7.00 p.m.

The Trapezium, or Orion Trapezium Cluster is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On February 4, 1617 he sketched three of the stars (A, C, D), but missed the surrounding nebulosity. The fourth component (B) was identified by several observers in 1673, and several more components were discovered later, for a total of eight by 1888. Subsequently several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5 inch aperture can resolve six stars under good seeing conditions. The Trapezium is a relatively young cluster that has formed directly out of the parent nebula. The five brightest stars are on the order of 15-30 solar masses in size. They are within a diameter of 1.5 light-years of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years. The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula situated south of Orion's Belt. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of 1,344 ± 20 light years and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light years across. Older texts frequently referred to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula. The Orion Nebula is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely studied celestial features. The nebula has revealed much about the process of how stars and planetary systems are formed from collapsing clouds of gas and dust. Astronomers have directly observed protoplanetary disks, brown dwarfs, intense and turbulent motions of the gas, and the photo-ionizing effects of massive nearby stars in the nebula. There are also supersonic "bullets" of gas piercing the dense hydrogen clouds of the Orion Nebula. Each bullet is ten times the diameter of Pluto's orbit and tipped with iron atoms glowing bright blue. They were probably formed one thousand years ago from an unknown violent event. The Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets. He therefore compiled a list of these objects, in collaboration with his assistant Pierre Méchain.

Pedro Castle 7th March 2011

The illustration above neatly fits what can be seen looking toward the south on observation night. The Winter Hexagon or Winter Circle/Oval is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux/Castor, Procyon, and Sirius. It is mostly upon the Northern Hemisphere's celestial sphere. On most locations on Earth (except the South Island of New Zealand and the south of Chile and Argentina and further south) this asterism is prominently in the sky from approximately December to March. In the tropics and southern hemisphere this (then called "summer hexagon") can be extended with the bright star Canopus in the south. Smaller and more regularly shaped is the Winter Triangle (also known as the Great Southern Triangle), an approximately equilateral triangle that shares two vertices (Sirius and Procyon) with the larger asterism. The third vertex is Betelgeuse. These three stars are three of the ten brightest objects, as viewed from Earth, outside the Solar System. Betelgeuse is also particularly easy to locate, being a shoulder of Orion, which assists stargazers in finding the triangle. Once the triangle is located, the larger hexagon may then be found. Several of the stars in the hexagon may also be found independently of one another by following various lines traced through various stars in Orion. The stars in the hexagon are parts of six constellations. Counter-clockwise around the hexagon, starting with Rigel, these are Orion, Taurus, Auriga, Gemini, Canis Minor, and Canis Major. Canopus , which our latitude fortunately enables us to see, is the brightest star in the southern constellation of Carina, and the second brightest star in the night-time sky, after Sirius. Since Canopus is so far south in the sky, it never rises in mid- or far-northern latitudes; in theory the northern limit of visibility is latitude 37°18' north. This is just south of Athens and San Francisco, and very close to Seville. It is almost exactly the latitude of Lick Observatory on Mt. Hamilton, California, from which it is readily visible due to the effects of elevation and atmospheric refraction, which add another degree to its apparent altitude. Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most luminous stars in our galaxy. Hipparcos established Canopus as lying 310 light years from our solar system. Canopus is 13,600 times more luminous than the Sun and the most intrinsically bright star within approximately 700 light years. In fact, from 1 astronomical unit, Canopus would have an apparent magnitude of -37. For most stars in the local stellar neighborhood, Canopus would appear to be one of the brightest stars in the sky. Canopus appears less bright than Sirius in our sky only because Sirius is much closer to the Earth (8.6 light years). To anyone living in the northern hemisphere, but far enough south to see the star, it served as a southern pole star. This lasted only until magnetic compasses became common. In modern times, Canopus serves another navigational use. Canopus' brightness and location well off the ecliptic makes it popular for space navigation. Many spacecraft carry a special camera known as a "Canopus Star Tracker" plus a sun sensor for altitude determination. To the right of the illustration (the west) Jupiter is setting low on the horizon. On March 12th through 16th, Mercury is close to Jupiter, just after sunset, and the smaller planet’s proximity to the giant makes it easy to find. Find a clear view to the west to observe this. Seven Mile beach would be ideal.

Pedro Castle, 7.00 p.m. Friday 4th February 2011

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with a mass slightly less than one-thousandth of the Sun but is two and a half times the mass of all the other planets in our Solar System combined.
Jupiter is classified as a gas giant along with Saturn, Uranus and Neptune. Together, these four planets are sometimes referred to as the Jovian planets.
The planet was known by astronomers of ancient times and was associated with the mythology and religious beliefs of many cultures. The Romans named the planet after the Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of −2.94, making it on average the third-brightest object in the night sky after the Moon and Venus. (Mars can briefly match Jupiter's brightness at certain points in its orbit.)
Jupiter is primarily composed of hydrogen with a quarter of its mass being helium; it may also have a rocky core of heavier elements. Because of its rapid rotation, Jupiter's shape is that of an oblate spheroid (it possesses a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding the planet is a faint planetary ring system and a powerful magnetosphere. There are also at least 63 moons, including the four large moons called the Galilean moons.
Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. The most recent probe to visit Jupiter was the Pluto-bound New Horizons spacecraft in late February 2007. The probe used the gravity from Jupiter to increase its speed. Future targets for exploration in the Jovian system include the possible ice-covered liquid ocean on the moon Europa.
The Galilean moons, easily visible even with modest magnification, are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance. They are among the most massive objects in the Solar System outside the Sun and the eight planets, with a radius larger than any of the dwarf planets. Ganymede, the largest of these moons, has a diameter greater than that of the planet Mercury.
The four moons were discovered sometime between 1609 and 1610 when Galileo made improvements to his telescope, which enabled him to observe celestial bodies more distinctly than had ever been possible before. Galileo’s discovery showed the importance of the telescope as a tool for astronomers by proving that there were objects in space that cannot be seen by the naked eye. More importantly, the incontrovertible discovery of celestial bodies orbiting something other than the Earth dealt a serious blow to the then-accepted Ptolemaic world system, or the geocentric theory in which everything orbits around the Earth.
Galileo initially named his discovery the Cosmica Sidera ("Cosimo's stars"), but names that eventually prevailed were chosen by Simon Marius. Marius claimed to have discovered the moons at the same time as Galileo, and gave them their present names in his Mundus Jovialis, published in 1614.
The planet is sinking lower in the evening sky, becoming invisible in April. On the eastern side of the sky, at dawn, Venus remains prominent, appearing as a brilliant "morning star," through March and beyond.
The glittery, bright "Winter Constellations" of Orion, Taurus, Auriga, Gemini, Canis Major, and Canis Minor are best seen during the early evening hours of late January and early February.

Pedro Castle, 6.30 p.m. Friday 7th January 2011

The constellation Perseus is in the northern half of the sky, neighbouring the distinctive asterisms that are Cassiopeia, Auriga and Taurus.
It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations defined by the International Astronomical Union. It contains the famous variable star Algol (β Per), and is also the location of the radiant of the annual Perseids meteor shower.
The brightest star of this constellation is also called Algenib (a name which is used for other stars as well, e. g. γ Peg). Mirfak (Arabic for elbow) is a supergiant of spectral type F5 Ib with an apparent brightness of 1.79m lying at a distance of ca. 590 light-years. Its luminosity is 5,000 times and its diameter is 42 times that of our sun.
One of the brightest and most interesting stars in Perseus is Algol. The name Algol means "demon star." Ancient skywatchers thought it was cursed because its brightness changes. That's because Algol — which is about 75 light-years from Earth — is the most famous "eclipsing binary" star. Today, astronomers know that Algol is two separate stars. About once every three days, the fainter member of the pair passes in front of the brighter one, and Algol grows fainter.
Perseus was a Greek hero most famous for his slaying of Medusa. If anyone looked at Medusa's face they would turn to stone. With the help of Hermes' wings and Athena's shield, Perseus killed Medusa without looking at her. On his way home, Perseus came across the monster, Cetus, getting ready to eat Andromeda. Perseus used Medusa's head to turn Cetus into stone and saved the princess.
With a little imagination, you can see the image of a man in the stars. He has a sort of triangular body, with two legs and feet that look like they are curling up towards the head. There are also two arms stretching out, possibly carrying some sort of weapon or the head of Medusa.
To the south in the sky, Jupiter is the brightest object, with the bright, unmistakable pattern of Orion rising in the east.