Pedro Castle, 2nd September 2011, 7.30

The illustration above shows the three day old Moon in the faint constellation of Libra.
The stars forming the triangle which the moon appears to be exiting are, from the “top”, Zubeneschamali, Zubenelgenubi, a visual binary, and Brachium, an eclipsing variable.
A much fainter star in the constellation of the Scales is Gliese 581, a red dwarf star with spectral type M3V, located 20.3 light years away from Earth. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least four, and possibly six, planets: Gliese 581 e, b, c, g (unconfirmed), d and f (unconfirmed).
Gliese 581 has been the subject of a "huge amount of attention" in the quest to discover the first habitable planet; in 2010, attention focused on unconfirmed planet g, which would have been close to the middle of the star's habitable zone, but more recently, in a study published in The Astrophysical Journal Letters, planet d "can be considered the first confirmed exoplanet that could support Earth-like life."
The star system first gained attention after Gliese 581 c, the first low-mass extrasolar planet found to be near its star's habitable zone, was discovered in April 2007. It has since been shown that under known terrestrial planet climate models, Gliese 581 c is likely to have a runaway greenhouse effect, and hence is probably too hot to be habitable, analogous to Venus. A subsequently discovered planet Gliese 581 d, may be just inside or just outside the outer boundary of the habitable zone (depending in part on the greenhouse properties of its atmosphere), analogous to Mars The discovery of exoplanet Gliese 581 e the least-massive planet known around a normal star, was announced in April 2009.
Excitement spiked again in September 2010 with the claimed discovery of Gliese 581 g, orbiting between c and d, believed to be the planet with the greatest likelihood of having conditions suitable for liquid water at its surface found to date because it is within the middle of the habitable zone. However, its existence was later put in "serious doubts" following further analysis.
The much more distinctive, and much larger, constellation of Scorpius follows Libra in the sky. Scorpius occupies an area of 497 square degrees and contains ten stars with known planets.
The brightest star in the constellation is alpha Scorpii, or Antares ("like Mars"), named for its reddish-orange colour, which resembles that of the planet Mars. Antares is a red supergiant with a radius about 800 times that of the Sun. It is classified as a variable star; its apparent magnitude varies between 0.9 and 1.8. It has a hot blue companion star about 2.9 arcseconds away. Antares is the 16th brightest star in the sky. It is approximately 600 light-years distant from Earth. It is also of the brightest stars near the ecliptic, the Sun’s apparent path in the sky.
The only planets in the night sky are Saturn, which is setting at viewing time, and Jupiter which does not rise until past 10 o’clock.

Pedro Castle, 1st August, 2011, 7.30

The Dawn probe has successfully entered orbit around the asteroid Vesta. Pictured above is the asteroid’s southern polar region, seen from a distance of about 10,500km
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones. They are grouped with the outer bodies as minor planets, which is the term preferred in astronomical circles
A meteoroid is a suggested term for a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are called a meteor shower.
A comet is an icy, small Solar System body which, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. Comets have been observed since ancient times and have traditionally been considered bad omens.
The probe has taken four years to get to Vesta and will spend the next year studying the huge rock before moving on to the "dwarf planet" Ceres.
Asteroid Vesta looks like a punctured football, the result of a colossal collision sometime in its past that knocked off its south polar region.
Vesta was discovered in 1807, the fourth asteroid to be identified in the great belt of rocky debris orbiting between Mars and Jupiter.
At the time, its great scale meant it was designated as another planet but it later lost this status as researchers learnt more about the diversity of objects in the Solar System.
Asteroids can tell us about the earliest days of the Solar System. These wandering rocks are often described as the rubble that was left over after the planets proper had formed.
Vesta and Ceres should make for interesting subjects. They are both evolved bodies - objects that have heated up and started to separate into distinct layers.
Vesta is thought to have a metal core in the centre - an iron core - and then silicate rock around it. Sometime in its history, it got banged on the bottom and a lot of material was liberated. Some of this material was pulled into the Earth's atmosphere. One in 20 meteorites seen to fall to Earth has been identified with Vesta.
Ceres, which, at 950km in diameter, is by far the largest and most massive body in the asteroid belt, probably did not evolve as much as Vesta.
Scientists think it likely that it retains a lot of water, perhaps in a band of ice deep below the surface.
Dawn's quest at Vesta over the coming months will be to map the asteroid's surface.
We will not be able to observe these small, dark objects, but Saturn is still visible, as are some distinctive asterisms. Scorpius is in the south, Ursa Major in the north, and the Summer Triangle is rising in the east.

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.