Pedro Castle, Thursday, 9th December 2010, 6.00 p.m.

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky reaches its northernmost or southernmost extremes. The name is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the apparent movement of the Sun's path north or south comes to a stop before reversing direction.
The winter solstice occurs exactly when the Earth's axial tilt is farthest away from the sun at its maximum of 22 1/2° 26'. Though the winter solstice lasts only an instant in time, the term is also colloquially used as midwinter or contrastingly the first day of winter to refer to the day on which it occurs. More evident to those in high latitudes, this occurs on the shortest day, and longest night, and the sun's daily maximum position in the sky is the lowest. The seasonal significance of the winter solstice is in the reversal of the gradual lengthening of nights and shortening of days. Depending on the shift of the calendar, the winter solstice occurs on December 21 or 22 each year in the Northern Hemisphere, and June 20 or 21 in the Southern Hemisphere.
Worldwide, interpretation of the event has varied from culture to culture, but most cultures have held a recognition of rebirth, involving holidays, festivals, gatherings, rituals or other celebrations around that time.

The solstice itself may have been a special moment of the annual cycle of the year even during neolithic times. Astronomical events, which during ancient times controlled the mating of animals, sowing of crops and metering of winter reserves between harvests, show how various cultural mythologies and traditions have arisen. This is attested by physical remains in the layouts of late Neolithic and Bronze Age archaeological sites such as Stonehenge in Britain and Newgrange in Ireland. (The picture above shows how the sunlight enters the tomb at Newgrange via the roofbox built above the door)
The primary axes of both of these monuments seem to have been carefully aligned on a sight-line pointing to the winter solstice sunrise (New Grange) and the winter solstice sunset (Stonehenge).
The winter solstice may have been immensely important because communities were not certain of living through the winter, and had to be prepared during the previous nine months. Starvation was common in winter between January and April, also known as the famine months. In temperate climates, the midwinter festival was the last feast celebration, before deep winter began. Most cattle were slaughtered so they would not have to be fed during the winter, so it was almost the only time of year when a supply of fresh meat was available. The majority of wine and beer made during the year was finally fermented and ready for drinking at this time. The concentration of the observances were not always on the day commencing at midnight or at dawn, but the beginning of the pre-Romanized day, which falls on the previous eve.
Before the scientific revolution many forms of observances; astronomical, symbolic or ritualistic, had evolved according to the beliefs of various cultures, many of which are still practiced today.
Weather permitting, this is how the sky will look on the observing night.

The Summer Triangle can still be clearly seen. It 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, being the brightest stars in the three constellations of Aquila, Cygnus, and Lyra The Great Square of Pegasus is overhead, with bright Jupiter to the south.

An Introduction To Astronomy Evening

Open to Everyone -Please Come along

26th Nov at 7:00 PM UCCI George Town

Cayman Islands

Pedro Castle , November 9th 6.30.

The illustration above comes from heavens-above.com, as it gives a picture of the most easily seen objects and patterns in the night sky for the day and time of the viewing session.

If you don’t already use the website, I cannot recommend it highly enough.

As shown, the small constellation Delphinus is directly over head. It is the small group of stars above the name on the chart above. It is on the edge of the Summer Triangle (see previous posts), and should be easy to find. Or so it looks.

Delphinus is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. It is one of the smaller constellations, ranked 69th in size out of 88. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical Union.

Delphinus's brightest stars form a distinctive asterism that can easily be recognized. It is bordered (clockwise from north) by Vulpecula the fox, Sagitta the arrow, Aquila the eagle, Aquarius the water-carrier, Equuleus the foal and Pegasus the flying horse.

The two brightest stars of this constellation, Sualocin (Alpha Delphini) and Rotanev (Beta Delphini), are not, as one might expect, names dating from antiquity, but instead date from a star catalogue of 1814 that was published at the Palermo Observatory in Italy. When read backwards they form the name Nicolaus Venator which is the Latinized version of the name of the assistant director of that observatory at that time, Niccolò Cacciatore (both Cacciatore and Venator mean hunter).

Delphinus is associated with two stories from Greek mythology. According to the first one, the Greek god Poseidon wanted to marry Amphitrite, a beautiful nereid. She, however, wanting to protect her virginity, fled to the Atlas Mountains. Her suitor then sent out several searchers, among them a certain Delphinus. Delphinus accidentally stumbled upon her and was able to persuade Amphitrite to accept Poseidon's wooing. Out of gratitude the god placed the image of a dolphin among the stars.

The second story tells of the Greek poet Arion of Lesbos (7th century BC), a court musician at the palace of Periander, ruler of Corinth. Arion had amassed a fortune during his travels to Sicily and Italy. On his way home from Tarentum his wealth caused the crew of his ship to conspire against him. Threatened with death, Arion asked to be granted a last wish which the crew granted: he wanted to sing a dirge. This he did, and while doing so, flung himself into the sea. There, he was rescued by a dolphin which had been charmed by Arion's music. The dolphin carried Arion to the coast of Greece and left.

The asterism is rather curious, for its four main stars form a rectangle called "Job's Coffin". This is probably a hang-over from the time Delphinus was interpreted as a whale, as in Chapter 41 of Job where God challenged Job: "Canst thou draw out leviathan with an hook?" However there is no reference to Job being swallowed by a whale, as happened with Jonah, so the name Job's Coffin remains a bit of a mystery.

Delphinus has several fine binaries and a very remote globular cluster.

Beta Delphini is a very close visual binary with orbit of 26.7 years.

Gamma¹ and gamma² Del form a fine binary with (perhaps) subtle colour change (observers argue over this; some find them both yellow, others that the companion is greenish or bluish).

NGC 7006 is a very remote globular cluster, perhaps as far as 200,000 light years away. Because of its distance it is extremely difficult to resolve. It is located fifteen arc minutes due east of gamma Delphini.

Much closer, and much brighter, is the planet Jupiter, unmistakable in an area of dim stars.

To compensate for the inclement weather conditions this year, we will be giving “An Introduction to Astronomy”, a presentation at the University College of the Cayman Islands, on Friday 26^th November, 7.00 p.m. in the Cascade Room.

Also, the society has a presence on Facebook now, feel free to join, and also the society.

There is now a very real reason for joining, in that only paid –up members will be notified of viewing sessions at a very dark,private site with the automated Meade.

CAYMAN ISLANDS ASTRONOMICAL SOCIETY: MEMBERSHIP FORM
NAME
ADDRESS
EMAIL
TEL # (s)

PLEASE SUBMIT WITH $25 TO:

Cayman Islands Astronomical Society

PO Box 584

Grand Cayman KY1-1502

Grand Cayman

Please make cheque payable to:

Cayman Islands Astronomical Society

NB: WE PREFER TO USE THE EMAIL ADDRESS AS THE PRIMARY CONTACT.

Pedro Castle, Wednesday 14th July 2010 7.30 pm

The third brightest star in the night sky, Arcturus is overhead as darkness falls. Look to the north, find the handle of the dipper as illustrated above, and follow the arc as shown above. Continue down to Spica, and follow the ecliptic to the west to find Saturn, Mars and Venus, which will be close to the Moon.
Arcturus, or Alpha Boötis, is located about 36.7 light-years from the Sun. It is the brightest star of Constellation Boötes, the Herdsman or Bear Driver, forming his left foot.
Boötes may be a hunter, on the tracks of the Great Bear, accompanied by his two dogs Asterion and Chara (the "Canes Venatici"). And yet the constellation was once known as Arctophylax which means the protector of the Bear. Perhaps it was the Romans who changed his role, for they called him Venator Ursae: the Bear Hunter.
Nowadays Boötes is generally considered to be a Herdsman (as in French: Le Bouvier), as he eternally shepherds the stars around the North Pole.
The constellation was known in antiquity, with the first recorded appearance being in Homer's Odyssey. In Book V Odysseus sails his ship by the stars, using the Pleiades, the Bear, and Boötes ("which set late") to reach his destination.
Arcturus is a type K1.5 IIIpe orange 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 visually 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.
Arcturus is notable for its high proper motion, larger than any first magnitude star in the stellar neighborhood other than α Centauri. It is moving rapidly (122 km/s) relative to the solar system, and is now almost at its closest point to the Sun. Closest approach will happen in about 4000 years, when the star will be a few hundredths of a light year closer to Earth than it is today. Arcturus is thought to be an old disk star, and appears to be moving with a group of 52 other such stars. Its mass is hard to exactly determine, but may be slightly larger than that of the Sun (1.1-0.4+0.6 solar mass). Arcturus is likely to be considerably older than the Sun, and much like what the Sun will be in its red giant phase.
53 probable members of a group of old disk stars appear to be moving with Arcturus.
Arcturus may be a Population II star and a member of the Milky Way galaxy's thick disk. The thick disk is generally formed of old stars that may lie several thousand light-years (ly) above or below the galactic plane, unlike thin disk stars such as the Sun which typically lie within a thousand ly. Such stars tend to have larger apparent motions, with rapid passages in highly inclined and elliptical orbits around the galactic core. Their movements tend to pierce the galactic disk that the Sun moves within, leading to a large relative motion. As they were born when the galaxy was less enriched or outside metal-rich thin disk areas, such stars also tend to be low in "metals," averaging around 25 percent of the Sun's. Thick disk stars make up only about four percent of all stars in the solar neighborhood
As the star is more massive than Sol, it has evolved faster into a helium-burning "clump" giant, possibly within five to eight billion years since hydrogen ignition. As a star that has evolved out of the "main sequence," Arcturus has fully shifted from the fusion of hydrogen to helium in at its core to the fusion of helium to carbon and oxygen, with trace activity of other nuclear processes. However, Arcturus is somewhat brighter than expected for a stable helium-burning star. Among the heavier elements and molecules detected in its stellar atmosphere have been iron (Fe-0.5) and CN. This helium-burning, orange-red giant stage is relatively brief, lasting tens to hundreds of million years (e.g., lasting around 700 million years for a star of one Solar mass like the Sun).
Eventually, the star will lose much of its current mass, from an intensified stellar wind that eventually puffs out its outer gas envelopes of hydrogen and helium (and lesser amounts of higher elements such as carbon and oxygen) into interstellar space as a planetary nebula. The result will be a planet-sized, white dwarf core that gradually cools and fades in brightness from the shutdown of thermonuclear fusion.
Prehistoric Polynesian navigators knew Arcturus as Hōkūleʻa, the "Star of Joy". Arcturus is the zenith star of the Hawaiian Islands. Using Hōkūleʻa and other stars, the Polynesians launched their double-hulled canoes from Tahiti and the Marquesas Islands. Traveling east and north they eventually crossed the equator and reached the latitude at which Arcturus would appear directly overhead in the summer night sky. Knowing they had arrived at the exact latitude of the island chain, they sailed due west on the trade winds to landfall. If Hōkūleʻa could be kept directly overhead, they landed on the southeastern shores of the Big Island of Hawaiʻi. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island. Since 1976, the Polynesian Voyaging Society's Hōkūle‘a has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.
The Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, and its appearance in the north signified the arrival of larvae of the wood-ant (a food item) in spring. The beginning of summer was marked by the star's setting with the sun in the west and the disappearance of the larvae. The star was also known as the mother of Djuit (Antares), and another star in Bootes, Weet-kurrk.

Pedro Castle, Tuesday, June 15th. 7.30 p.m. 2010

The constellation Corona Borealis is found nearly midway between Arcturus and Vega; a little closer to the first of these stars. It is characterized by a half-moon shaped line of stars, among which Gemma is conspicuous, similar to a precious stone on the crown (this star is also known with the name of Alphecca), which is a 2.2 magnitude star 75 light years away.

Although faint, the constellation is quite easy to make out.

The loop of nine stars from Pi to Rho Coronae Borealis was known in China as Guansuo, the prison for working-class miscreants; the prison for the upper classes was more auspiciously placed farther north, in Ursa Major.

Corona Borealis was sometimes considered to represent a crown that was given by Dionysus to Ariadne, the daughter of Minos of Crete. At other points it was considered to belong, in a sense, to Boötes, the herdsman. The Cheyenne nation of Native Americans called it the "Camp Circle" as they arranged their camps in a semicircle. In Welsh mythology, the Northern Crown was called Caer Arianrhod, ‘the Castle of the Silver Circle,’ and was the heavenly abode of the Lady Arianrhod.

Venus, Mars and Saturn are still bright in the sky.

Pedro Castle, Sunday, 16th May 2010, 7.30 p.m.

The sky is brilliant in the early evenings this month with three planets and bright stars along the line of the ecliptic.
The ecliptic is the apparent path that the Sun traces out in the sky during the year, appearing to move eastwards on an imaginary spherical surface, the celestial sphere, relative to the (almost) fixed stars.
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the celestial equator and the celestial poles.
Most planets go in orbits around the sun, which are almost in the same plane as the Earth's orbital plane, differing by a few degrees at most. As such they always appear close to the ecliptic when seen in the sky.
The name ecliptic arises because eclipses occur when the full or new Moon is very close to this path of the Sun.

On the 16th, Venus will be close to the crescent Moon in the west. Moving eastwards along the ecliptic, the Twins of Gemini, Castor and Pollux, come before Mars.
Saturn is roughly halfway between Regulus, in the constellation Leo, and Spica, α Virginis.
The distinctive constellation of Ursa Major is high in the north, and Crux, the Southern Cross is in the south.

Pedro Castle,April 18th, 7.00 p.m. 2010

Canis Minor, as shown above on the sky chart, is a small constellation which was included in the 2nd century astronomer Ptolemy's 48 constellations, and is still included among the 88 modern constellations. Its name is Latin for "smaller dog" in contrast to Canis Major, the larger dog, and it is commonly represented as one of the dogs following the constellation of Orion the hunter

Canis Minor contains only two bright stars, Procyon, which means "before the dog" in Greek, as it rises an hour before the 'Dog Star', Sirius, of Canis Major, and Gomeisa.

Procyon is the brighter of the two. To the naked eye, it appears to be a single star, the eighth brightest in the night sky with a visual apparent magnitude of 0.34. It is actually a binary star system, consisting of a white main sequence star, named Procyon A, and a faint white dwarf companion of spectral type DA, named Procyon B. The reason for its brightness is not its intrinsic luminosity but its closeness to the Sun; at a distance of 3.5 pc or 11.41 light years, Procyon is one of our near neighbours.

Procyon forms one of the three vertices of the Winter Triangle, along with Sirius and Betelgeuse.

Procyon A is a white star of spectral type F5; it is 1.4 times the mass, twice the diameter, and 7.5 times more luminous than the Sun. It is bright for its spectral class, suggesting that it is a subgiant that has completely fused its core hydrogen into helium, and begun to expand as "burning" moves outside the core. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years. It is expected that the Sun will also go through this process when hydrogen fusion ceases at its core.

The chart also shows the four planets visible. Mercury might be a little hard to see on Sunday, but it has been visible for the last two weeks.

This is a list of the 20 brightest stars as seen from the Earth (not including the Sun). The stars are numbered from 1 to 20 in sequence.

	Common Name	Constellation	Apparent Magnitude	Spectral Type	Luminosity (Sun = 1)	Distance (Light Years)	Radial Velocity (km / sec)
1	Sirius	Canis Major	-1.46	A1	26	8.7	-8
2	Canopus	Carina	-0.72	F0	15,000	310	+21
3	Alpha Centauri	Centaurus	-0.04	G2	1.7	4.3	-22
4	Arcturus	Boötis	0.00	K2	115	36	-5
5	Vega	Lyra	0.03	A0	52	25	-14
6	Capella	Auriga	0.08	G8 F0	90 70	43	+30
7	Rigel	Orion	0.12	B8	60,000	910	+21
8	Procyon	Canis Minor	0.38	F5	7	11.4	-3
9	Achernar	Eridanus	0.46	B5	400	85	+19
10	Betelgeux	Orion	0.0 - 0.9	M2	105,000 v	640	+21
11	Agena	Centaurus	0.61	B1	10,000	460	-11
12	Altair	Aquila	0.77	A7	10	16.6	-26
13	Acrux	Crux Australis	0.83	B1	3,200	360	-11
14	Aldebaran	Taurus	0.85	K5	120	68	+54
15	Antares	Scorpius	0.96	M1	7,500	330	-3
16	Spica	Virgo	0.98	B1	2,100	260	+1
17	Pollux	Gemini	1.14	K0	60	36	+3
18	Fomalhaut	Piscis Australis	1.16	A3	13	22	+7
19	Deneb	Cygnus	1.25	A2	70,000	1,800	-5
20	Becrux	Crux Australis	1.25	B0	8,200	425	+20