Pedro Castle, December 16, 2012, 6.30

              In last months newsletter I noted that the bright star Alpheratz, shown above, is shared between the constellations Pegasus and Andromeda.
         Andromeda is famous for containing the Andromeda galaxy, shown as the red oval marked M31 above, within its boundaries.
    This spiral galaxy is the nearest to our Milky Way galaxy, but not the closest galaxy overall. At an apparent magnitude of 3.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects, making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution, approximately 2.5 million light-years (2.4×1019 km) from Earth
       The Andromeda Galaxy is the largest galaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, the Andromeda Galaxy may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and could be the most massive in the grouping. The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars: at least twice the number of stars in the Milky Way galaxy, which is estimated to be 200–400 billion.
      The Andromeda Galaxy is approaching the Milky Way at about 100 to 140 kilometres per second (62 to 87 mi/s) which is about 1.96 billion to 2.74 billion miles per year, making it one of the few blueshifted galaxies. The Andromeda Galaxy and the Milky Way are thus expected to collide in about 4.5 billion years, although the details are uncertain since Andromeda's tangential velocity with respect to the Milky Way is known to only within about a factor of two.
      Two scientists with the Harvard–Smithsonian Center for Astrophysics stated that when, and even whether, the two galaxies collide will depend on Andromeda's transverse velocity. Based on current calculations they predict a 50% chance that in a merged galaxy the solar system will be swept out three times farther from the galactic core than it is currently located. They also predict a 12% chance that the Solar System will be ejected from the new galaxy some time during the collision. Such an event would have no adverse effect on the system and chances of any sort of disturbance to the Sun or planets themselves may be remote.
       Without intervention, by the time that the two galaxies collide, the surface of the Earth will have already become far too hot for liquid water to exist, ending all terrestrial life, which is currently estimated to occur in about 1.4 billion years due to gradually increasing luminosity of the Sun.
        Jupiter is bright in the eastern sky at viewing time, close to the bright star Aldebaran, Alpha Tauri, in the ascending constellation of Taurus.

Pedro Castle, November 16, 2012

      High in the sky as darkness falls is the constellation Pegasus. 
      Four stars of nearly equal brightness make up the asterism known as the “Great Square of Pegasus”, Scheat, Alpheratz, Markab and Algenib.
      The "Great Square" forms the body of the Winged Horse. To connect the rest of Pegasus, you'll need to use the right side of the "square." Pegasus is flying upside down across the sky. From Markab (lower right corner) extends the head of the Winged Horse.  
   The two front legs of Pegasus can be found off the star Scheat (upper right corner).  
   The star Alpheratz is shared by two constellations, Pegasus and Andromeda. The star is actually considered to be a star of Andromeda.

The Babylonian constellation IKU  had four stars of which three were later part of the Greek constellation Hippos (Pegasus). Pegasus, in Greek mythology, was a winged horse with magical powers. One myth regarding his powers says that his hooves dug out a spring, Hippocrene, which blessed those who drank its water with the ability to write poetry. Pegasus was the one who delivered Medusa's head to Polydectes, after which he travelled to Mount Olympus in order to be the bearer of thunder and lightning for Zeus. Eventually, he became the horse to Bellerophon, who was asked to kill the Chimera and succeeded with the help of Athena and Pegasus. Despite this success, after thedeath of his children, Bellerophon asked Pegasus to take him to Mount Olympus. Though Pegasusagreed, he plummeted back to Earth after Zeus either threw a thunderbolt to buck him off.
     In ancient Persia, Pegasus was depicted by al-Sufi as a complete horse facing east, unlike most other uranographers, who had depicted Pegasus as half of a horse, rising out of the ocean.
    In Hindu astronomy, the Great Square of Pegasus contained the 26th and 27th lunar mansions. More specifically, it represented a bedstead that was a resting place for the Moon.
   Warrau and Arawak peoples in Guyana used the stars in the Great Square to represent a grill on stilts.
     51 Pegasi, a star in this constellation, is the first Sun-like star known to have an extrasolar planet. IK Pegasi is the nearest supernova candidate.
    Messier 15 or M15 (shown on the illustration above) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 12.0 billion years old, it is one of the oldest known globular clusters.
      M15 is about 33,600 light-years from Earth, and 175 light years in diameter. It has an absolute magnitude of -9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as 'core collapse' and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.                                                                                                                        
      Home to over 100,000 stars, the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15 C. M15 also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928. Just three others have been found in globular clusters since then.
     Pegasus is also noted for its more unusual galaxies and exotic objects. Einstein's Cross is a quasar that has been lensed by a foreground galaxy. The elliptical galaxy is 400 million light-years away with a redshift of 0.0394, but the quasar is 8 billion light-years away. The lensed quasar resembles a cross because the gravitational force of the foreground galaxy on its light creates four images of the quasar.
      A quasi-stellar radio source ("quasar") is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than extended sources similar to galaxies. While the nature of these objects was controversial until as recently as the early 1980s, there is now a scientific consensus that a quasar is a compact region in the center of a massive galaxy surrounding its central supermassive black hole. Its size is 10–10,000 times the Schwarzschild radius of the black hole. The quasar is powered by an accretion disc around the black hole.
        Stephan's Quintet is another unique object located in Pegasus. It is a cluster of five galaxies at a distance of 300 million light-years and a redshift of 0.0215. First discovered by Édouard Stephan, a Frenchman, in 1877, the Quintet is unique for its interacting galaxies. Two of the galaxies in the middle of the group have clearly begun to collide, sparking massive bursts of star formation and drawing off long "tails" of stars. Astronomers have predicted that all five galaxies may eventually merge into one large elliptical galaxy.

                   ASTRONOMICAL SOCIETY: OCTOBER 2012
                
       Weather permitting; we will meet on Thursday, 18th October, 6.30 p.m. at Pedro Castle.
If the sky is more than 50% cloud covered, we cancel. This can be, as you will appreciate, a sometimes difficult decision.
    Almost directly overhead at viewing time is the constellation Aquila.  Aquila lies just a few degrees north of the celestial equator and is located along the Milky Way. Because of this location along the line of our galaxy, many clusters and nebulae are found within its borders, but they are dim and there are few galaxies.
    Astronomers observed two major novae in Aquila, the first one being in 389 BC. It was recorded as brighter than the planet Venus. The second one was observed in the year 1918 (Nova Aquilae). It was brighter than Altair. A nova should not be confused with a supernova. A nova is an old star that brightens temporarily, and a supernova (dying star) is a massive star exploding.                                                      NASA’s Pioneer 11 mission will pass near one of constellation Aquila’s stars in about four million years.                                                                                                                                                  Altair (Alpha Aquila), the brightest star of the constellation, is a multiple star system. It is about eight times brighter than the sun and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitude of 0.77. Class A stars are among the more common naked eye stars, and are white or bluish-white. Other examples include Sirius, Deneb, Vega and Fomalhaut.  Altair is located 16.7 light-years (5.13 parsecs) from Earth and is one of the closest stars visible to the naked eye. Altair is a type-A main sequence star with approximately 1.8 times the mass of the Sun and 11 times its luminosity. Altair possesses an extremely rapid rate of rotation; it has a rotational period of approximately 9 hours. For comparison, the equator of the Sun requires just over 25 days for a complete

                  CAYMAN ISLANDS ASTRONOMICAL SOCIETY
                         NEWSLETTER; OCTOBER 2012
       Weather permitting; we will meet on Thursday, 18th October, 6.30 p.m. at Pedro Castle.
If the sky is more than 50% cloud covered, we cancel. This can be, as you will appreciate, a sometimes difficult decision.
    Almost directly overhead at viewing time is the constellation Aquila.  Aquila lies just a few degrees north of the celestial equator and is located along the Milky Way. Because of this location along the line of our galaxy, many clusters and nebulae are found within its borders, but they are dim and there are few galaxies.
    Astronomers observed two major novae in Aquila, the first one being in 389 BC. It was recorded as brighter than the planet Venus. The second one was observed in the year 1918 (Nova Aquilae). It was brighter than Altair. A nova should not be confused with a supernova. A nova is an old star that brightens temporarily, and a supernova (dying star) is a massive star exploding.                                                     
    NASA’s Pioneer 11 mission will pass near one of constellation Aquila’s stars in about four  million years.
                                                                                                                                                   Altair (Alpha Aquila), the brightest star of the constellation, is a multiple star system. It is about eight times brighter than the sun and the twelfth brightest star in the night sky. It is an A-type main sequence star with an apparent visual magnitude of 0.77. Class A stars are among the more common naked eye stars, and are white or bluish-white. Other examples include Sirius, Deneb, Vega and Fomalhaut.  Altair is located 16.7 light-years (5.13 parsecs) from Earth and is one of the closest stars visible to the naked eye. Altair is a type-A main sequence star with approximately 1.8 times the mass of the Sun and 11 times its luminosity. Altair possesses an extremely rapid rate of rotation; it has a rotational period of approximately 9 hours. For comparison, the equator of the Sun requires just over 25 days for a complete

The name Altair comes from the Arabic al-nasr al-ta’ir, meaning ‘flying eagle’ or ‘vulture’. Ptolemy called this star Aetus, the eagle, the same as the constellation. The German scholar Paul Kunitzsch notes that the Babylonians and Sumerians referred to Altair as the eagle star, testimony to an even more ancient origin of the name. Altair’s neighbouring stars Beta and Gamma Aquilae lie in the eagle’s neck and in its left shoulder respectively, according to Ptolemy’s description. These two stars have their own names, Alshain and Tarazed, which come from a Persian translation of an old Arabic word meaning ‘the balance’.
           In China, Altair and its two flanking stars, Beta and Gamma Aquilae, were known as Hegu, a large battle drum – beating the drum was a signal for the army to attack. The line to the south formed by Theta, 62, 58 and Eta Aquilae was Tianfu, the drumstick. Delta Aquilae and surrounding stars including Mu, Sigma and Iota were Youqi, a banner flying on the right side of the drum, while the stars of Sagitta to the north were a banner on the left of the drum.
    Altair and its attendant stars also had two other identifications. In one they were known as the Three Generals, the commanding officer in the centre flanked by two subordinates.

Aquila represents an eagle, the thunderbird of the Greeks. There are several explanations for the presence of this eagle in the sky. In Greek and Roman mythology, the eagle was the bird of Zeus, carrying (and retrieving) the thunderbolts which the wrathful god hurled at his enemies. But the eagle was involved in love as well as war.
   According to one story, Aquila is the eagle that snatched up the beautiful Trojan boy Ganymede, son of King Tros, to become the cup-bearer of the gods on Olympus. Authorities such as the Roman poet Ovid say that Zeus turned himself into an eagle, whereas others say that the eagle was simply sent by Zeus. Ganymede himself is represented by the neighbouring constellation of Aquarius, and star charts show Aquila swooping down towards Aquarius. Germanicus Caesar says that the eagle is guarding the arrow of Eros (neighbouring Sagitta) which made Zeus love-struck.

Pedro Castle, September 19th, 7.00 p.m. 2012

Mars will be very close to the crescent moon in the faint constellation of Libra on viewing night.  Libra was known in Babylonian astronomy as MUL Zibanu ("the scales"), or alternatively as the Claws of the Scorpion. The scales were held sacred to the sun god Shamash, who was also the patron of truth and justice. It was also seen as the Scorpion's Claws in ancient Greece. Since these times, Libra has been associated with law, fairness and civility. In Arabic zubānā means "scorpion's claws", and likely similarly in other Semitic languages: this resemblance of words may be why the Scorpion's claws became the Scales.

    Alternatively, another source says the Romans made it into a separate constellation in the time of Julius Caesar. Since then the Scales of Libra have become regarded as the symbol of justice, held aloft by the goddess of justice, Astraea. One legend identifies Astraea with the neighbouring figure of Virgo.

     The two brightest stars, the alpha and beta of the constellation, are called Zubenelgenubi and Zubeneschamali respectively. Zubeneschamali, the northern one of the two, comes from an Arabic phrase meaning "the northern claw," that of the Alpha star meaning "the southern claw”.

    The illustration above comes from Alexander Jamieson’s Celestial Atlas which appeared in February 1822, with a second edition following in September that same year. For all the fame that the Atlas achieved, its author remains little known. He evidently had a wide knowledge of science, mathematics and languages, for he wrote a number of educational works on subjects as diverse as cartography, logic, rhetoric, algebra, mechanics and hydrostatics as well as editing a Latin dictionary and running a series of private schools

   Jamieson was born in Rothesay on the Isle of Bute, west Scotland, in 1782, the son of a wheelwright. He obtained MA and LLD degrees from Marischal College, Aberdeen, in 1821 and 1823. In 1825 he became a mature student at St John’s College Cambridge but there is no record that he ever resided there or obtained any degree. In fact, he seems to have spent most of his working life in and around London as a writer, teacher and finally an actuary.

     Venus shines bright in the east before long before dawn, and Jupiter is overhead, close to the red giant star Aldebaran in the constellation Taurus.

Cayman Islands Astronomical Society News Letter

 No observing sessions are planned for the immediate future.
The chart above is for 8.00 p.m. 05th August and applies all month.
Perhaps the most interesting spectacle this month, and a naked eye event, will be the changing pattern formed by Saturn, Mars and the bright star Spica, shown by the white dot beside Mars.
The brightest constellations, and easy ones to make out, at that time of the evening, are Sagittarius and Scorpio in the south, and Cygnus, the Swan, or Northern Cross high in the NE.
Cygnus contains the bright star Deneb, which forms a point of the Summer Triangle, an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega, being the brightest stars in the three constellations of Aquila, Cygnus, and Lyra.

The English term was popularized by British astronomer Sir Patrick Moore in the 1950s, although he did not invent it. The Austrian astronomer Oswald Thomas described these stars as "Grosses Dreieck" (Great Triangle) in the late 1920s and "Sommerliches Dreieck" (Summerly Triangle) in 1934. The asterism was remarked upon by J. J. Littrow, who described it as the "conspicuous triangle" in the text of his atlas (1866), and Bode connected the stars in a map in a book in 1816, although without label.
The Perseid meteor shower peaks on the night 11-12 August, conveniently a Saturday night, Sunday morning for those of you who want to stay up late.

Pedro Castle, Friday 22nd June, 2012

The viewing of the Transit of Venus was, if you weren’t there, a huge success. Fortunately, we had seven telescopes for more than a thousand people to look through, and the atmosphere was orderly and convivial.

    Early risers can see Venus and Jupiter before and in the dawn, while Saturn, Mars and Mercury are visible when darkness falls.

      Saturn is close to the 15^th brightest star in the sky, Spica, which lies in the constellation of Virgo. Roughly halfway between this brilliant duo and the star Regulus in Leo, Mars glows distinctly in an area of dim stars. Mercury is visible as the sun sets, a good excuse to go the beach for the waning of the day.

    Further north from this line of the ecliptic, the bright star Arcturus is unmistakable. In the illustration above it is the alpha, α, orange star in the kilt of the Herdsman, Boötes.

    In ancient Babylon the stars of Boötes were known as SHU.PA. They were apparently depicted as the god Enlil, who was the leader of the Babylonian pantheon and special patron of farmers.

    Exactly whom Boötes is supposed to represent in Greek mythology is not clear. According to one version, he was a ploughman who drove the oxen in the constellation Ursa Major using his two dogs Chara and Asterion (from the constellation Canes Venatici). The oxen were tied to the polar axis and so the action of Boötes kept the heavens in constant rotation.

     The Boötes void, or the Great Void is a huge and approximately spherically shaped region of space, containing very few galaxies. It is located in the vicinity of the constellation Boötes, hence its name. At nearly 250 million light-years in diameter (approximately 0.27% of the diameter of the visible universe), the Boötes void is one of the largest known voids in the universe, and is referred to as a supervoid. According to astronomer Greg Aldering, the scale of the void is such that "If the Milky Way had been in the center of the Boötes void, we wouldn't have known there were other galaxies until the 1960s."

   The Boötes Dwarf Galaxy is a faint, satellite galaxy of the Milky Way located in Boötes about 197 000 light-years  away from Earth.

     To the naked eye, orange-yellow Arcturus has a visual magnitude of −0.04, making it the brightest star north of the celestial equator, and the fourth brightest star in the night sky, after −1.46 magnitude Sirius, −0.86 magnitude Canopus, and −0.27 magnitude Alpha Centauri. However, Alpha Centauri is a bright binary star, whose unresolved components to the naked eye are both fainter than Arcturus. This makes Arcturus the third brightest individual star, just ahead of Alpha Centauri A (α Cen A), whose visual magnitude is −0.01.

     The apparent (visual) magnitude (m) of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere. The brighter the object appears, the lower the value of its magnitude.