Pedro Castle, October 30th 6.30 p.m.

This is what the sky will look like at 7.00 on viewing night.
I am going to continue with the theme of the Summer Triangle while it is still high in the early evening sky.
The alpha star of Aquila, Altair, is a vertex of the Summer Triangle asterism.
Aquila (Latin: eagle; sometimes named the Vulture), is one of the 48 constellations listed by Ptolemy, also mentioned by Eudoxus (4th century BC) and Aratus (3rd century BC) and now also part of the list of 88 constellations acknowledged by the IAU. It lies roughly at the celestial equator.
NASA's Pioneer 11 mission, which flew by Jupiter and Saturn (in 1974 and 1979 respectively) will pass near one of the stars in the constellation in about four million years.

The constellation resembles a wide winged, soaring, short necked, bird, which the ancients identified as an eagle. In classical Greek mythology, it was identified as the eagle which carried the thunderbolts of Zeus and was sent by him to carry the shepherd boy Ganymede who he desired, represented by the neighbouring Aquarius, to Mount Olympus where he became the wine-pourer for all the gods. This explains why the largest moon of Jupiter was called Ganymede, Jupiter being the Roman name of Zeus. The eagle was used to carry or retrieve the lightning bolts that were thrown by Zeus.
In the Chinese love story of Qi Xi, Niu Lang (Altair) and his two children (β and γ Aquilae) are separated forever from their wife and mother Zhi Nu (Vega in Lyra, another vertex of the Summer Triangle) who is on the far side of the river, the Milky Way.
In Hinduism, the constellation Aquila is identified with the half eagle, half human deity, Garuda.
Altair (α Alpha Aquilae) is the brightest star in the constellation Aquila and the twelfth brightest star in the nighttime sky, at visual magnitude 0.77. It is an "A" type or white star located 17 light-years (5.2 pc) away from Earth, one of the closest stars visible to the naked eye.
The name "Altaïr" is Arabic for "the bird". The spelling "Atair" is also used frequently. The name was given by Arabic astronomers and adopted by Western astronomers.

Pedro Castle,Thursday, 2nd October, 7.00 p.m.

As darkness falls on viewing night, the constellation of Cygnus, the Swan, is overhead, in the orientation that is shown above, up being north.
Because of the pattern of its main stars, it is sometimes known as the Northern Cross (in contrast to the Southern Cross).
One of the most recognizable constellations of the northern summer and autumn, it resembles a swan flying south along the Milky Way. Albireo, a double star with blue and yellow components is at the "head". Deneb, its brightest star, is at the tail and is one star of the summer triangle.
The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega. This triangle connects the constellations of Aquila, Cygnus, and Lyra.
Looking toward the south, Jupiter, the fourth brightest object in the sky, is in the constellation of Sagittarius. Venus is setting in the west.

Wednesday 3rd September 2008. Pedro Castle 7.30 pm

There are “winds” in space as well as around the Cayman Islands, albeit of a very different nature.
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star.
Different types of stars have different types of stellar winds.
Post-main sequence stars nearing the ends of their lives often eject large quantities of mass in massive slow winds. These include red giants and supergiants, and asymptotic giant branch stars. These winds are likely to be driven by radiation pressure on dust condensing in the upper atmosphere of the stars.
G stars like the Earth's Sun have a wind driven by their hot, magnetized corona. The Sun's wind is called the solar wind. These winds consist mostly of high-energy electrons and protons (about 1 keV) that are able to escape the star's gravity because of the high temperature of the corona.
Massive stars of types O and B have stellar winds with lower mass loss rates but very high velocities. Such winds are driven by radiation pressure on the resonance absorption lines of heavy elements such as carbon and nitrogen. These high-energy stellar winds blow stellar wind bubbles.
Although stellar winds from main sequence stars do not strongly influence the evolution of the stars, during the later, post-main sequence phase, mass lost by stellar winds can decide the fate of the star. Many intermediate mass stars become white dwarfs at the ends of their lives rather than exploding as supernovae only because they lost enough mass in their winds.
A Stellar wind bubble is the astronomical term usually used to describe a cavity light years across filled with hot gas blown into the interstellar medium by the high-velocity (several thousand km/s) stellar wind from a single massive star of type O or B. Weaker stellar winds still blow bubble structures though, and these are also called astrospheres.
The heliosphere blown by the solar wind, within which all the major planets of the Solar System are embedded, is in fact a small example of a stellar wind bubble.

Above is a Hubble Space Telescope image of a bubble-like cavity, called N44F, 35 light-years in diameter, which is being inflated by a stellar wind from a very hot star once buried inside a cold dense cloud. The central star in N44F is ejecting mass at a rate greater than a 100 million times that in the solar wind. The particles in this stellar wind move at 7 million kilometers per hour, compared with about 1.5 million km per hour in the case of the Sun. N44F is located about 160,000 light-years away in the Large Magellanic Cloud.
Jupiter will be high in the south on Wednesday, easily spotted in the Teapot of Sagittarius, which is pouring onto the tail of the scorpion, Scorpius.

Pedro Castle, Monnday, 4th August 2008

The constellation Hercules is overhead when darkness falls. Although it holds no first magnitude stars, it is easy to distinguish the “Keystone” asterism.
Hercules contains two of the most conspicuous globular clusters: M13, the brightest globular cluster in the northern hemisphere, and M92.
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is derived from the Latin globulus—a small sphere. A globular cluster is sometimes known more simply as a globular.
Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk. Globular clusters are fairly common; there are about 158 currently known globular clusters in the Milky Way, with perhaps 10–20 more undiscovered. Large galaxies can have more: Andromeda, for instance, may have as many as 500. Some giant elliptical galaxies, such as M87, may have as many as 10,000 globular clusters. These globular clusters orbit the galaxy out to large radii, 40 kiloparsecs (approximately 131 thousand light-years) or more.
The Great Globular Cluster in Hercules was discovered by Edmond Halley in 1714, and catalogued by Charles Messier on June 1, 1764.
Its real diameter is about 145 light-years, and at its distance of 25,100 light years, its angular diameter of 20' corresponds to a linear 145 light years - visually, it is perhaps 13' large, and it is composed of several hundred thousand stars.
There are seven stars in Hercules known to be orbited by extrasolar planets. They were discovered in 1996, 2005, 2006, and the last four in 2007.
Four of the planets in our solar system are visible in the night sky, Venus setting in the west, closely followed by Saturn and Mars, and Jupiter can be seen in the south, close to the “Teapot” of Sagittarius.

Pedro Castle, Sunday, 6th July 2008

We will aim to meet 7.30. p.m. on Sunday 6th July at Pedro Castle.
However, it is the rainy season. If the sky is more than 50% cloud covered we cancel. Given the changeableness of the weather, you can appreciate that this can sometimes be a difficult decision to make.
In the west Saturn, Mars, the bright star Regulus and the Moon will all be close to each other in the sky when darkness falls. Jupiter will be rising in the east.
Close to the zenith, Arcturus is the most luminous object in that part of the night sky.
The brightest star in the constellation Boötes, it is the third brightest star in the night sky, with a visual magnitude of −0.05, after Sirius and Canopus. It is the second brightest star visible from northern latitudes and the brightest star in the northern celestial hemisphere.
Researching Arcturus led me to this wonderful piece of astronomical lore, quite new to me.
The Local Interstellar Cloud, casually called the Local Fluff, is the interstellar cloud (roughly 30 light years across) through which our solar system is currently moving. The cloud has a temperature of 6000° C, about the same temperature as the surface of the Sun. It is very thin, with 0.26 atoms per cubic centimeter; approximately one-fifth the density of the galactic interstellar medium and twice that of the gas in the Local Bubble. In comparison, Earth's atmosphere at STP has 2.7 × 1019 molecules per cubic centimeter.
The Sun, with a few other local stars, is embedded in the Local Fluff. Notable nearby planetary systems include those of Alpha Centauri, Vega, Arcturus, and Fomalhaut.
Our Sun may exit the Local Interstellar Cloud during the next 10,000 years. Much remains unknown about the local ISM, including details of its distribution, its origin, and how it affects the Sun and the Earth, although it is thought that the Local Interstellar Cloud's effects on Earth are effectively cancelled by the solar wind and the Sun's magnetic field.
Arcturus is a type K1.5 IIIpe red giant star — the letters "pe" stand for "peculiar emission," which indicates that the spectrum of light given off by the star is unusual and full of emission lines. This is not too uncommon in red giants, but Arcturus has a particularly strong case of the phenomenon. It is at least 110 times more luminous than the Sun, but this underestimates its strength as much of the "light" it gives off is in the infrared; total power output is about 180 times that of the Sun. The lower output in visible light is due to a lower efficacy as the star has a lower surface temperature than the Sun.
Its mass is hard to exactly determine, but may be about the same as the Sun, and is no more than 1.5 solar masses. Arcturus is likely to be considerably older than the Sun, and much like what the Sun will be in its red giant phase.
According to the Hipparcos satellite, Arcturus is 36.7 light years (11.3 parsecs) from Earth, relatively close in astronomical terms. Hipparcos also suggested that Arcturus is a binary star, with the companion about twenty times dimmer than the primary and orbiting close enough to be at the very limits of our current ability to make it out. Recent results remain inconclusive, but do support the marginal Hipparcos detection of a binary companion.

Pedro Castle, Thursday June 5th, 7.30 p.m.

Crux, the Southern Cross, will be visible for the rest of this month. On the night of the 5th, the constellation will be hanging above the southern horizon.
Crux is the smallest constellation in the sky, but one of the most celebrated. The early Portuguese navigators saw it as a symbol of their faith, and the mystery of the unknown lent it an additional charm in the minds of those from whom the southern skies were hidden. There are other cross patterns formed by stars, but the distinguishing feature of the two bright pointers alpha and beta Centauri make Crux unmistakable.
Crux lies in a dense and brilliant part of the Milky Way, which makes the famous dark nebula known as the Coalsack striking in silhouette against the star background.
This is the head of the Emu to the native aborigines of Australia. The rest of the Emu is made from the dark lanes in the Milky Way.
Alpha Crucis was too far south to have been given an ancient name so Acrux is simply a combination of the A in alpha and Crux. Being of first magnitude (0.83), it is the 12th brightest star in the sky and 321 light years distant from us. Under high power, a telescope reveals it to be a binary system with two very similar B type stars having magnitudes of 1.33 and 1.73 separated by 4 arc seconds. With surface temperatures of around 27,000K they are highly luminous, the brightest 25,000 time more luminous than our Sun. In fact, the brighter star is itself a double, the two component stars orbit each other every 76 days but are too close to split with a telescope. So Acrux is a triple star system. A further, type B4, star lies 90 arc seconds away and may belong to the system as well. It has a similar proper motion - that is, its direction of motion through space - but is probably a more distant star that just happens to lie in the same direction.
NGC 4755 (k, kappa Crucis) is an open cluster of stars, that contains about 100 stars and is about 10 million years old. It lies some 7500 light years away and spans a 10 arc minutes field of view so filling a volume of space about 20 light years across. Lying close to Beta Crucis, it is easy to find and best seen with binoculars or a telescope at low power. It contains many highly luminous blue-white stars along with a central red supergiant that makes a beautiful colour contrast. It was named the Jewel box by Sir John Herschel who called it a "casket of variously coloured precious stones". It can easily be seen by the unaided eye as a star, and indeed was originally catalogued as such in pre-telescope times.
Saturn and Mars are visible in a line (called the ecliptic) with the three day old crescent Moon.
The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year. The orbit of the Moon is inclined by about 5° on the ecliptic. The moon crosses the ecliptic about twice per month. If this happens during new moon a solar eclipse occurs, during full moon a lunar eclipse. This was the way the ancients could trace the ecliptic along the sky; they marked the places where eclipses could occur and the name ecliptic is derived from being the place where eclipses occur.

Pedro Castle,Thursday, 8th May

The familiar constellation of the Great Bear, Ursa Major, is visible in the north, although it may appear “upside down” to anyone from the higher latitudes.
The seven brightest stars, located in the Bear's hindquarters and tail, form the well-known Big Dipper asterism. (In Britain, this asterism is known as the Plough.) The stars Merak (β Ursae Majoris) and Dubhe are known as the "pointer stars" because they are helpful for finding Polaris, also known as the North Star. By visually tracing a line from Merak through Dubhe and continuing, one's eye will land on Polaris, accurately indicating true north.
Mizar, a star in the Big Dipper, forms the famous optical double star with Alcor.
Several bright galaxies are found in Ursa Major, including the pair Messier 81 (one of the brightest galaxies in the sky) and Messier 82 above the bear's head, and Pinwheel Galaxy (M101), a beautiful spiral northwest of η Ursae Majoris.
Polaris, sometimes known as the Lodestar, is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole (42′ away as of 2006), making it the current northern pole star.
Polaris has the common reputation of being the brightest star in the sky, whereas near dead-on second magnitude (2.02) it comes in at number 48. Its lower rank, however, is largely determined by its great distance of 430 light years. The star is actually an evolved class F (F7) yellow supergiant 2500 times more luminous than our Sun with a temperature of about 6000 Kelvin, which leads to a radius 45 times that of the Sun and a mass of six times solar. Hydrogen fusion has stopped in the star's core, and it is now passing through a phase of instability wherein it pulsates over a period of about four days, almost invisibly changing its brightness as the brightest "Cepheid" variable star in the sky.
Polaris has the distinction of having a pair of companions, one near, the other far. About 18 seconds of arc away lies an eighth magnitude F3 1.4 (or so) solar mass dwarf, which at the distance of Polaris must be at least 2400 Astronomical Units away and take at least 42,000 years to orbit. Much closer is an F7 dwarf (noted from spectroscopy and resolved by the Hubble Space Telescope, giving us three F stars in one pot), that at a measured average distance of only 17 AU takes but 29.6 years to go around, a high eccentricity running it between 27 and 6.7 AU.