Archive for July, 2010

Our summer almanac 30.07.2010 – 05.08.2010

Posted in astronomical time on July 30, 2010 by espacelab

More shooting stars
Keep looking out for the Perseid shooting stars, as they can include some of the most spectacular heavenly displays of the year.

NGC 7742
This unusual galaxy is a face-on unbarred spiral galaxy in the constellation Pegasus, and is unusual in that it contains a ring but no bar. O. K. Sil’chenko and A. V. Moiseev proposed that the ring was formed partly as the result of a merger event in which a smaller gas-rich dwarf galaxy collided with NGC 7742. As evidence for this, they point to the unusually bright central region, the presence of highly-inclined central gas disk, and the presence of gas that is counterrotating (or rotating in the opposite direction) with respect to the stars.

It is a type of galaxy called a Seyfert galaxy, a class of galaxies with nuclei that produce spectral line emission from highly ionized gas, named after Carl Keenan Seyfert, the astronomer who first identified the class in 1943. The centres of Seyfert galaxies form a subclass of active galactic nuclei (AGN), and are thought to contain supermassive black holes with masses between 107 and 108 solar masses.

Naming a month and stealing a Day for an Emperor
Why do the successive months of July and August have 31 days each when other months have alternate lengths of 30 days and 31 days? The answer has to do with flattering an emperor! On January 1 in the year 45 BC Julius Caesar instituted his reform of the Roman calendar, but soon after his death a year later in 44 BC, the calendar became inaccurate again due to the counting of leap years every three years instead of four.

In the year 8 BC Julius Caesar’s successor, the first Roman emperor Augustus, rectified this error by ordering the cancellation of the next three leap years, so that by the year 8 AD the calendar would be restored to its proper time. In the spirit of calendar reform, the Roman Senate went on to rename the month of Sextilis in honour of Augustus, but they decided that the new month of August should have an equal number of days as the month that honours his predecessor Julius Caesar.

This was achieved by taking a day from February, leaving it with 28 days, and switching the lengths of September, October, November and December, so that the very convenient system of alternating 30 day and 31 day months was completely messed up. What we are left with now is:

Thirty days hath September,
April, June and November,
February has twenty-eight alone
All the rest have thirty-one.
Excepting leap year – that’s the time
When February’s days are twenty-nine.

Lammas Day
In some English-speaking countries in the Northern Hemisphere, August 1 is Lammas Day (loaf-mass day), the festival of the wheat harvest, and is the first harvest festival of the year. On this day it was customary to bring to church a loaf made from the new crop. In many parts of England, tenants were bound to present freshly harvested wheat to their landlords on or before the first day of August. In the Anglo-Saxon Chronicle, where it is referred to regularly, it is called “the feast of first fruits”. The blessing of new fruits was performed annually in both the Eastern and Western Churches on the first or the sixth of August (the latter being the feast of the Transfiguration of Christ).

Lammas is also a Neo-Pagan holiday, often called Lughnasadh, celebrating the first harvest and the reaping of grain. It is a cross-quarter holiday halfway between the Summer Solstice (Litha) and the Autumnal Equinox (Mabon).

The Wheel of the Year
The Wheel of the Year is a Wiccan and Neopagan term for the annual cycle of the Earth’s seasons. It consists of eight festivals, spaced at approximately even intervals throughout the year. These festivals are referred to by Wiccans as Sabbats (pronounced /ˈsæbət/). While the term Sabbat originated from Abrahamic faiths such as Judaism and Christianity and is of Hebrew origin, the festivals themselves have historical origins in Celtic and Germanic pre-Christian feasts, and the Wheel of the Year, as has developed in modern Neopaganism and Modern Wicca, is really a combination of the two cultures’ solstice and equinox celebrations. When melded together, two somewhat unrelated European Festival Cycles merge to form eight festivals in modern renderings.

A flat Earth?
The Flat Earth model is a view that the Earth’s shape is a flat plane or disk, and is supported by ou much overvalued “common sense“. In the stories of the ancient Mesopotamians and the ancient Greeks the world was flat.

The early Greek maps such as those of Anaximander and Hecataeus of Miletus, describe the world in similar way.

The Hebrew Bible carried forward the ancient Middle Eastern cosmology, such as in the Enuma Elish, which described a flat earth with a solid roof, surrounded by water above and below, as illustrated by references to the “foundations of the earth” and the “circle of the earth”.

The Enûma Eliš is the Babylonian creation myth (named after its opening words). It was recovered by Austen Henry Layard in 1849 (in fragmentary form) in the ruined Library of Ashurbanipal at Nineveh (Mosul, Iraq), and published by George Smith in 1876. The text is composed of about a thousand lines and is recorded in Old Babylonian on seven clay tablets, each holding between 115 and 170 lines of text. Most of Tablet V has never been recovered, but aside from this lacuna the text is almost complete. A duplicate copy of Tablet V has been found in Sultantepe, ancient Huzirina, located near the modern town of Şanlıurfa in Turkey. This epic is one of the most important sources for understanding the Babylonian worldview. The first tablet begins:

When the sky above was not named,
And the earth beneath did not yet bear a name,
And the primeval Apsû, who begat them,
And chaos, Tiamat, the mother of them both,
Their waters were mingled together,
And no field was formed, no marsh was to be seen;
When of the gods none had been called into being.

However, early Greek philosophers alluded to a spherical Earth and by around 330 BC, Aristotle provided observational evidence for the spherical Earth, noting that travelers going south see southern constellations rise higher above the horizon. He argued that this was only possible if their horizon was at an angle to northerners’ horizon and that the Earth’s surface therefore could not be flat.

It has been suggested that seafarers probably provided the first observational evidence that the Earth was not flat. Writing around 10 BC, the Greek geographer Strabo cited various phenomena observed at sea as suggesting that the Earth was spherical. He observed that elevated lights or areas of land were visible to sailors at greater distances than those less elevated, and stated that the curvature of the sea was obviously responsible for this. He also remarked that observers can see further when their eyes are elevated, and cited a line from the Odyssey (“As he rose on the swell he looked eagerly ahead, and could see land quite near.”) as indicating that the poet Homer was already aware of this as early as the 7th or 8th century BC.

In the second century BC, Crates of Mallus devised a terrestrial sphere which divided the earth into four continents, separated by great rivers or oceans, with people presumed to be living in each of the four regions.

Lucretius (1st. century BC) opposed the concept of a spherical Earth, because he considered that in an infinite universe there was no center towards which heavy bodies would tend, thus he considered the idea of animals walking around topsy-turvy under the Earth to be absurd.

But by the 1st century AD, Pliny the Elder was in a position to claim that everyone agrees on the spherical shape of Earth, although there continued to be disputes regarding the nature of the antipodes, and how it is possible to keep the ocean in a curved shape. Pliny also considers the possibility of an imperfect sphere, “shaped like a pinecone”.

In the second century the Alexandrian astronomer Ptolemy advanced many arguments for the sphericity of the Earth. Among them was the observation that when sailing towards mountains, they seem to rise from the sea, indicating that they were hidden by the curved surface of the sea. He also gives separate arguments that the Earth is curved north-south and that it is curved east-west. Ptolemy derived his maps from a curved globe and developed the system of latitude, longitude, and climes. His writings remained the basis of European astronomy throughout the Middle Ages, although Late Antiquity and the Early Middle Ages (ca. 3rd to 7th centuries) saw occasional arguments in favor of a flat Earth.

In Europe in the ages following the Greeks and the Romans there are different ideas, but a recent study of medieval concepts of the shape of the Earth notes that since the eighth century, no cosmographer actually interested in the subject questioned the the idea that world was a sphere, that it was global!

Picture from a 1550 edition of On the Sphere of the World

In our summer almanac first post of July we mentioned Johannes de Sacrobosco, who produced “On the Sphere of the World”, the most influential astronomy textbook of the 13th century and required reading by students in all Western European universities, described the world as a sphere.

A world map by Muhammad al-Idrisi (1100-1166) depicts the Earth as round.

Introductory summary overview map from al-Idrisi’s 1154 world atlas. Note that south is at the top of the map.

In the Islamic world Abū Rayhān al-Bīrūnī (973-1048) solved a complex geodesic equation to accurately compute the Earth’s circumference, which was close to modern values of the Earth’s circumference. His estimate of 6,339.9 kilometres (3,939.4 mi) for the Earth radius was only 16.8 km (10.4 mi) less than the modern value of 6,356.7 km (3,949.9 mi). In contrast to his predecessors who measured the Earth’s circumference by sighting the Sun simultaneously from two different locations, al-Biruni developed a new method that used trigonometric calculations based on the angle between a plain and mountain top. This yielded more accurate measurements of the Earth’s circumference, and made it possible for a single person to measured it from a single location.

The myth of the Flat Earth
The myth of the Flat Earth is the modern misconception that the prevailing cosmological view during the Middle Ages saw the Earth as flat, instead of spherical.

James Hannam in his book “Science Versus Christianity?” wrote:
The myth that people in the Middle Ages thought the earth is flat appears to date from the 17th century as part of the campaign by Protestants against Catholic teaching. But it gained currency in the 19th century, thanks to inaccurate histories such as John William Draper’s History of the Conflict Between Religion and Science (1874) and Andrew Dickson White’s History of the Warfare of Science with Theology in Christendom (1896). Atheists and agnostics championed the conflict thesis for their own purpose …

The first accounts of the legend have been traced to the 1830s. In 1828, Washington Irving‘s highly romanticised and inaccurate biography, The Life and Voyages of Christopher Columbus, was published and mistaken by many for a scholarly work. In Book III, Chapter II of this biography, Irving gave a largely fictional account of the meetings of a commission established by the Spanish sovereigns to examine Columbus’s proposals. One of his more fanciful embellishments was a highly unlikely tale that the more ignorant and bigoted members on the commission had raised scriptural objections to Columbus’s assertions that the Earth was spherical.

Martin Behaim‘s Erdapfel, the oldest surviving terrestial globe and finished before the news of the discovery of the Americas had reached Europe (1492), demonstrates that knowledge of the round earth was common on the continent before.

In reality, the issue in the 1490s was not the shape of the Earth, but its size, and the position of the east coast of Asia, as Irving in fact points out.

Solar Flare 01.08.2010
Astronomers from all over the world witnessed the huge flare above a giant sunspot the size of the Earth, which they linked to an even larger eruption across the surface of Sun.

The solar fireworks at the weekend were recorded by several satellites, including Nasa’s new Solar Dynamics Observatory which watched its shock wave rippling outwards. The explosion, called a coronal mass ejection, was aimed directly towards Earth, which then sent a “solar tsunami” racing 93 million miles across space.

Images from the SDO hint at a shock wave travelling from the flare into space, the New Scientist reported. Experts said the wave of supercharged gas will likely reach the Earth on Tuesday, when it will buffet the natural magnetic shield protecting Earth. It is likely to spark spectacular displays of the aurora or northern and southern lights.


Our summer almanac 23.07.2010 – 29.07.2010

Posted in astronomical time on July 23, 2010 by espacelab

Our summer almanac makes mention of Vega (α Lyr / α Lyrae / Alpha Lyrae) regularly as it is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun’s neighborhood.

The name of this star comes from a loose transliteration of the Arabic word wāqi‘ meaning “falling” or “landing”, via the phrase an-nasr al-wāqi‘ “the alighting vulture”. The constellation was represented as a vulture in ancient Egypt, and as an eagle or vulture in ancient India.

Vega has been extensively studied by astronomers, leading it to be termed “arguably the next most important star in the sky after the Sun.” Vega was the northern pole star around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14′. Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was one of the first stars whose distance was estimated through parallax measurements.

Stars, dust and debris
Vega is an interesting star in the discovery of excess infrared flux coming from Vega, beyond what would be expected from the star alone in one of the early results from the Infrared Astronomy Satellite (IRAS). The Infrared Astronomical Satellite[2] (IRAS) was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths.

Launched on January 25, 1983, its mission lasted ten months. The telescope was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC).

Following the discovery of an infrared excess around Vega, other stars have been found that display a similar anomaly that is attributable to dust emission. As of 2002, about 400 of these stars have been found, and they have come to be termed “Vega-like” or “Vega-excess” stars. It is believed that these may provide clues to the origin of the Solar System.

By 2005, the Spitzer Space Telescope had produced high resolution infrared images of the dust around Vega. It was shown to extend out to 43″ (330 AU) at a wavelength of 24 μm, 70″ (543 AU) at 70 μm and 105″ (815 AU) at 160 μm. These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1–50 μm in size. The estimated total mass of this dust is 3 × 10−3 times the mass of the Earth. Production of the dust would require collisions between asteroids in a population corresponding to the Kuiper Belt around the Sun. Thus the dust is more likely created by a debris disk around Vega, rather than from a protoplanetary disk as was earlier thought.

Artist’s concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega.

Dark Matter and Shooting Stars
From July 27 until August 17 it is worth looking out for the meteor shower called the Perseids. Look toward the north east after midnight and see if you can find the constellation Perseus. It is because these shooting stars appear in a part of the night sky close to this constellation that this meteor shower is called the Perseids.

When we look out at our Universe we see stars and galaxies, and the more we explore deep into space, the more we find, but there is also a lot more mass and material in the Universe we cannot see. Even though we can’t see this mass and material, astronomers have calculated that it must be there having observed the gravitational motions of stars and galaxies, and that this missing mass must be about 20 times the amount visible as starlight.

Astronomers and cosmologists call this missing mass ‘Dark Matter’. This ‘missing matter’ was first discovered in the 1920’s when a Dutch astronomer called Jan Oort was measuring the speed of stars as they move in the disc of our galaxy. He was expecting to find them moving up and down in the galactic disc as they turn with the galaxy. He found that stars do indeed move in this way, but not as much as he expected, so he concluded that there must be a lot more matter in the disc of the galaxy than had previously been calculated. Jan Oort worked out that if the disc of the Milky Way had about 50% more matter than previously anticipated, then that would explain the movement of the stars he had observed.

In the 1970’s and 80’s, the American astronomer Vera Rubin was looking at other galaxies, studying the speed of stars as they orbit around various galactic discs. She expected to find that the further out from the centre stars were, the slower the star speeds would be. Instead they found that the orbital speed of stars was more or less constant. From this discovery they calculated that each galaxy must be surrounded by a halo of invisible material, weighing 10 times as much as the bright disc. What this dark matter actually is still puzzles astronomers and cosmologists today, but there are some very interesting theories and experiments going on to try and answer this question.

Dharma day
Dharma day on July 26 marks the beginning of the Buddha’s teaching. The word Dharma can be translated as truth and is the term used for the path to enlightenment, or the Buddhist teaching. Soon after his Enlightenment the Buddha went to find his former disciples and share his experience with them. This event could be seen as the start of the Buddhist religion, and is what Dharma day celebrates.

The first teaching to the Buddha’s original five disciples is known as “The First Turning of the Wheel of the Dharma (Dharmachakra).”

In early Buddhism, the time around what has now become Dharma Day (the eighth lunar month in the traditional Indian calendar) marked the beginning of the rainy season. At this point, the Buddha and his monks and nuns would suspend their nomadic lifestyle for three months. They would shelter together until the monsoon season was over, and use this time as a period of further meditation and reflection. At the end of this time, they would resume their travelling, passing on the Buddha’s teachings to those who were interested.

Dharma day is now seen as a chance to express gratitude that the Buddha, and other enlightened teachers, have shared their knowledge with others. Dharma day is usually celebrated with readings from the Buddhist scriptures, and is an opportunity to reflect deeply on their content.

Monsoon rains in modern Varanasi

Rainy seasons at home and away
Our wet weather days are connected to rainfall and heatwaves across the globe by the jet stream. The publication New Scientist makes connections between the floods and forest fires with our own dreary wet summer days:

Raging wildfires in western Russia have reportedly doubled average daily death rates in Moscow. Diluvial rains over northern Pakistan are surging south – the UN reports that 6 million have been affected by the resulting floods. It now seems that these two apparently disconnected events have a common cause. They are linked to the heatwave that killed more than 60 in Japan, and the end of the warm spell in western Europe. The unusual weather in the US and Canada last month also has a similar cause. According to meteorologists monitoring the atmosphere above the northern hemisphere, unusual holding patterns in the jet stream are to blame. As a result, weather systems sat still. Temperatures rocketed and rainfall reached extremes.

Monsoon winds are getting stronger as the northern hemisphere warms. Climate reconstructions reveal unprecedented warming in the last century, however little is known about trends in aspects such as the monsoon. Studies that have reconstructed the monsoon winds for the last 1,000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea, found that monsoon wind strength has increased during the past 4 centuries, as the northern hemisphere has warmed.

Our summer almanac 16.07.2010 – 22.07.2010

Posted in astronomical time on July 16, 2010 by espacelab

Regulus (α Leo / α Leonis / Alpha Leonis) is the brightest star in the constellation Leo and one of the brightest stars in the nighttime sky, and lies approximately 77.5 light years from Earth. Regulus is a multiple star system composed of four stars which are organised into two pairs.

Rēgulus is Latin for ‘prince’ or ‘little king’. The Greek variant Basiliscus is also used. It is known as Qalb Al Asad, from the Arabic قلب لأسد or Qalb[u] Al-´asad, meaning ‘the heart of the lion’. This phrase is sometimes approximated as Kabelaced and translates into Latin as Cor Leōnis. It is known in Chinese as 轩辕十四, the Fourteenth Star of Xuanyuan, the Yellow Emperor. In Hindu astronomy, Regulus corresponds to the Nakshatra Magha.
Persian astrologers around 3000 BC knew Regulus as Venant, one of the four ‘royal stars’. It was one of the fifteen Behenian stars known to medieval astrologers, associated with granite, mugwort, and a kabbalistic symbol.

Summer Stars
Looking in the night sky this week it is worth trying to find some of the bright stars of summer. In the north-northeastern part of the sky you may find the constellation Cygnus, the Swan. The brightest star in this star pattern is called Deneb and is one of the largest known super-giant stars. Deneb is 25 times as big and 60,000 times brighter than our Sun.

Look out for the bright star Vega in the constellation Lyra in the eastern sky. This star pattern can be found looking northeast at about 22.30h. It is to be found almost overhead late on July evenings. Vega has a brilliant bluish colour, and that together with its brightness makes it easy to recognize. Vega is only 25 light years away and is the fifth brightest star in the night sky. Vega is a brilliant blue-white star, two and a half times the size of our Sun, and twice as hot.

Only a few years after the invention of photography in the 1830’s the star Vega became the first star ever to be photographed through a telescope. American astronomers in the Harvard Observatory in Massachusetts USA made the photograph using the 15 inch refractor.

The Sky at Night
Have you ever wondered why the sky is dark at night? If space went on to infinity, and it was filled with stars, then everywhere you looked in the night sky there would be a star! If the night sky was filled with starlight then there would be no darkness, only light! A nineteenth-century German astronomer called Heinrich Olbers suggested that the darkness we see at night is due to the fact that we look out through gaps between stars. In what became known as the ‘Olbers’ paradox ‘, he suggested in 1823, incorrectly, that there must be an edge to the Universe, and that beyond that edge there were no stars, only dark empty space.

In February 1848, a brilliant amateur scientist, Edgar Allen Poe, better known today as the author of tales of ghoulish, gothic horror, gave a lecture setting out the solution to Olbers’ paradox. Even though his solution fits so well with current ideas about the Universe, his ideas were not taken up seriously in his own time. What Poe quite ingeniously realized was that by looking further out into space we are looking further back in time, to that time in the story of the Universe before stars were born.

Olbers’ edge in space turns out to be an edge in time. The darkness of the night sky means that the Universe was born at a definite moment in time.

According to Edward R Harrison, the first to conceive of anything like the paradox was Thomas Digges, who was also the first to exposit the Copernican system in English and may have been the first to postulate an infinite universe with infinitely many stars. Kepler also posed the problem in 1610, and the paradox took its mature form in the 18th century work of Halley and Cheseaux.

Although the paradox is commonly attributed to the German amateur astronomer Heinrich Wilhelm Olbers, who described it in 1823, but Harrison shows convincingly that Olbers was far from the first to pose the problem, nor was his thinking about it particularly valuable. Harrison argues that the first to set out a satisfactory resolution of the paradox was Lord Kelvin, in a little known 1901 paper, and that Edgar Allan Poe’s essay Eureka (1848) curiously anticipated some qualitative aspects of Kelvin’s argument:

Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy – since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all.

Looking towards the centre of our galaxy

The night sky at this time of year is full of stars of our galaxy the Milky Way. This is because on summer nights our view of space is directed towards the centre of our galaxy.

Space exploration in our part of the galaxy
In our last post we mentioned how European spacecraft Rosetta raced past the Lutetia asteroid at 15 km/s completing the flyby in just a minute. But the cameras and other instruments had been working for hours and in some cases days beforehand, and will continue afterwards. Shortly after closest approach, Rosetta began transmitting data to Earth for processing.

Lutetia has been a mystery for many years. Ground telescopes have shown that it presents confusing characteristics. In some respects it resembles a ‘C-type’ asteroid, a primitive body left over from the formation of the Solar System. In others, it looks like an ‘M-type’. These have been associated with iron meteorites, are usually reddish and thought to be fragments of the cores of much larger objects.

The new images and the data from Rosetta’s other instruments will help to decide but not tonight. Compositional information is needed for that.

This project has even bigger ambitions though. ESA’s Rosetta spacecraft will be the first to undertake the long-term exploration of a comet at close quarters. It comprises a large orbiter, which is designed to operate for a decade at large distances from the Sun, and a small lander. Each of these carries a large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted.

After entering orbit around Comet 67P/Churyumov-Gerasimenko in 2014, the spacecraft will release a small lander onto the icy nucleus, then spend the next two years orbiting the comet as it heads towards the Sun. On the way to Comet Churyumov-Gerasimenko, Rosetta will receive gravity assists from Earth and Mars, and will fly past main belt asteroids.

Why ‘Rosetta’?
The European Space Agency’s unprecedented mission of cometary exploration is named after the famous ‘Rosetta Stone’. This slab of volcanic basalt – now in the British Museum in London – was the key to unravelling the civilisation of ancient Egypt.

French soldiers discovered the unique Stone in 1799, as they prepared to demolish a wall near the village of Rashid (Rosetta) in Egypt’s Nile delta. The carved inscriptions on the Stone included hieroglyphics – the written language of ancient Egypt – and Greek, which was readily understood. After the French surrender in 1801, the 762-kilogram stone was handed over to the British, and so now everyone can see it in the British Museum in London.

By comparing the inscriptions on the stone, historians were able to begin deciphering the mysterious carved figures. Most of the pioneering work was carried out by the English physician and physicist Thomas Young, and the French scholar Jean François Champollion. As a result of their breakthroughs, scholars were at last able to piece together the history of a long-lost culture.

Just as the Rosetta Stone provided the key to an ancient civilisation, so ESA’s Rosetta spacecraft will unlock the mysteries of the oldest building blocks of our Solar System – the comets. As the worthy successor of Champollion and Young, Rosetta will allow scientists to look back 4600 million years to an epoch when no planets existed and only a vast swarm of asteroids and comets surrounded the Sun.

Tisha B’Av (Jewish )
Tuesday 20 July is a solemn day that commemorates a series of tragedies that have befallen the Jewish people over the years, many of which have coincidentally happened on this day.

Discovery of the most massive star ever is announced 21 July
R136a1 is a blue hypergiant star, currently on record as the most massive star known, at an estimated 265 solar masses.

The star also holds the record for the most luminous at 8,700,000 times the luminosity of the Sun. It is a member of R136, a super star cluster near the center of the 30 Doradus complex (also known as the Tarantula Nebula), in the Large Magellanic Cloud. The mass of the star was determined by astronomers at the University of Sheffield.

Left to right: a red dwarf, the Sun, a blue dwarf, and R136a1. R136a1 is not the largest known star in terms of volume; this distinction belongs to VY Canis Majoris.

Our summer almanac 09.07.2010 – 15.07.2010

Posted in astronomical time on July 9, 2010 by espacelab

The Pinwheel Galaxy (also known as Messier 101 or NGC 5457) is a face-on spiral galaxy distanced 23 million light-years away in the constellation Ursa Major.

M101 is a relatively large galaxy compared to the Milky Way. With a diameter of 170,000 light-years it is nearly twice the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small bulge of about 3 billion solar masses.

Exploring the Milky Way
July 10 saw Europe’s Rosetta space probe fly past the Asteroid Lutetia, returning a stream of scientific data for analysis. The rock – some 120km (75 miles) in its longest dimension – is the biggest asteroid yet visited by a satellite.

Pictures showed Lutetia to be quite irregular in shape, its surface marked by a number of wide impact craters and even some intriguing grooves.

Asteroid Lutetia has been revealed as a battered world of many craters. ESA’s Rosetta mission has returned the first close-up images of the asteroid showing it is most probably a primitive survivor from the violent birth of the Solar System.

The flyby was a spectacular success with Rosetta performing faultlessly. Closest approach took place at 18:10 CEST, at a distance of 3162 km. The images show that Lutetia is heavily cratered, having suffered many impacts during its 4.5 billion years of existence. As Rosetta drew close, a giant bowl-shaped depression stretching across much of the asteroid rotated into view. The images confirm that Lutetia is an elongated body, with its longest side around 130km.

Rosetta’s encounter with the asteroid occurred some 454 million km from Earth, beyond the orbit of Mars.

Martyrdom of the Báb
The Bahá’í Faith is a monotheistic religion founded by Bahá’u’lláh in nineteenth-century Persia, emphasizing the spiritual unity of all humankind. There are an estimated five to six million Bahá’ís around the world in more than 200 countries.

This major holy day is celebrated on the 9th July at noon and commemorates the events surrounding the death of the Báb in 1850. The Báb (a title meaning ‘the Gate’) had many followers but his beliefs did not meet with approval from the leaders of the state religion in Persia, and they decided he should be taken from prison and put to death.

One of his young followers begged to be allowed to share his fate, and this wish was granted. An Armenian firing squad lined up and shot at the Báb and his follower, but when the smoke cleared, the young follower remained there unharmed and the Báb had gone. The Báb was found back in his cell, and the soldiers were so shaken by the ‘miracle’ that they refused to try to kill him again so a new regiment had to be called for. This time, when the squad opened fire the Báb and the follower died, and their bodies were thrown into a moat outside the town. The remains of the Báb were brought secretly from Iran to the Holy Land and were eventually interred in the tomb built for them in a spot specifically designated by Bahá’u’lláh. The Báb’s tomb, located in Haifa, Israel, is an important place of pilgrimage for Bahá’ís.

To commemorate this day, Bahá’ís read special prayers at noon, which is the time the execution was scheduled for. This is also a day of rest, when Bahá’ís should not work.

Nineteen months make a year
The Bahá’í calendar is based upon the calendar established by the Báb. The year consists of 19 months, each having 19 days, with four or five intercalary days, to make a full solar year. The Bahá’í New Year corresponds to the traditional Persian New Year, called Naw Rúz, and occurs on the vernal equinox, March 21, at the end of the month of fasting. Bahá’í communities gather at the beginning of each month at a meeting called a Feast for worship, consultation and socializing. Each of the 19 months is given a name which is an attribute of God; some examples include Bahá’ (Splendour), ‘Ilm (Knowledge), and Jamál (Beauty). The Bahá’í week is familiar in that it consists of seven days, with each day of the week also named after an attribute of God. Bahá’ís observe 11 Holy Days throughout the year, with work suspended on 9 of these. These days commemorate important anniversaries in the history of the religion.

St Swithin’s Day (Christian )
Swithin (or Swithun) was a Saxon bishop in the 9th century. Legend has it that the weather on his feast day, 15 July, will determine the weather for the next 40 days.

Saint Swithin was a Saxon bishop. He was born in the kingdom of Wessex and educated in its capital, Winchester. He was famous for charitable gifts and building churches. His feast day is 15 July and his emblems are rain drops and apples.

Swithin was chaplain to Egbert, the 802-839 king of Wessex. Egbert’s son Ethelwulf, whom Swithin educated, made him bishop of Winchester in 852.

Only one miracle is attributed to Swithin while he was alive. An old lady’s eggs had been smashed by workmen building a church. Swithin picked the broken eggs up and, it is said, they miraculously became whole again.

Swithin died on 2 July 862. According to tradition, he had asked to be buried humbly. His grave was just outside the west door of the Old Minster, so that people would walk across it and rain fall on it in accordance with Swithin’s wishes.

On 15 July 971, though, Swithin’s remains were dug up and moved to a shrine in the cathedral by Bishop Ethelwold. Miraculous cures were associated with the event, and Swithin’s feast day is the date of the removal of his remains, not his death day.

However, the removal was also accompanied by ferocious and violent rain storms that lasted 40 days and 40 nights and are said to indicate the saint’s displeasure at being moved. This is probably the origin of the legend that if it rains on Saint Swithin’s feast day, the rain will continue for 40 more days.

Saint Swithin is still seen as the patron of Winchester Cathedral.

Jet Streams
Our weather this summer is dominated by the Polar Front Jet Stream, a strong band of winds in the upper atmosphere that effectively controls the weather in high latitudes in the northern hemisphere. It is the mechanism for forming high and low pressure systems at the surface of the Earth, and consequently has a major influence on the Atlantic depressions that bring the UK much needed year round rainfall.

Meteorologists studying the upper atmosphere above the northern hemisphere have drawn a link between the wildfires raging across western Russia and the dramatic flooding in northern Pakistan, pinning the blame on an unusual ‘kink’ in the polar jet stream that has remained frozen in place for more than a month.

A jet stream is a fast-moving current of air that wiggles around the world at an altitude of around 10 and 12 kilometres above ground. There’s two branches usually in place in the northern hemisphere at this time of year — a strong “subtropical” jet blowing over the Mediterranean and central Asia, and a weaker northern “polar” jet that blows over northern Europe (and carries with it the low pressure areas that bring the UK most of its rain).

Weather forecasters use the polar jet to predict medium-term temperatures, because it acts as a barrier between cold Arctic air and warmer tropical air. If the polar jet moves north then areas just south of it will be warmer and drier than normal. If it moves south, then areas just to the north will be cooler and wetter.

During this July 2010, an exceptionally strong polar jet stream has shot up to the north of Moscow, and then plunged back south towards Pakistan. This brought hot air north over western Russia, and stopped low pressure systems from dropping their rain on the region, where harvests normally depend on it.

Our summer almanac 02.07.2010 – 08.07.2010

Posted in astronomical time on July 9, 2010 by espacelab

Polaris is the most important star for finding the cardinal directions of east, west, north and south, as it remains in a fixed position in the night sky above the North Pole.

The only deep sky object in this constellation is the Ursa Minor Dwarf dwarf elliptical galaxy. It was discovered by A.G. Wilson of the Lowell Observatory in 1954. It is part of the Ursa Minor constellation, and a satellite galaxy to the Milky Way. The galaxy consists mainly of older stars and there appears to be little to no ongoing star formation in the Ursa Minor Dwarf galaxy.

The Planck mission
Nearly 13 months ago on the 5 June 2009 the ESA’s Planck satellite carried out a critical mid-course manoeuvre that will placed the satellite on its final trajectory for arrival at L2, the second Lagrange point of the Sun-Earth system, early in July.

The Lagrange points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects such as a satellite and where it is positioned in relation to the Earth and Moon. The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the right kind of centripetal force required to rotate with them, so they allow an object to be in a “fixed” position in space rather than move around in an orbit in which its relative position is constantly changing.

The Sun–Earth L2 is a good spot for space-based observatories, because an object around L2 will maintain the same orientation with respect to the Sun and Earth’s night time side of the planets surface, and so shielding and calibration of these delicate instruments are much simpler. This position is still far away from Earth so solar radiation is not completely blocked by the shadow of the Earth.

Planck cruising to L2
Credits: ESA – D. Ducros

The manoeuvre was scheduled to begin at 19:28 CEST on 5 June 2009, and lasted up to 30 hours.

Coolest spacecraft ever in orbit around L2
On 3 July 2009 the detectors of Planck’s High Frequency Instrument reached their amazingly low operational temperature of -273.05°C, making them the coldest known objects in space. The spacecraft has also just entered its final orbit around the second Lagrange point of the Sun-Earth system, L2.

Planck is equipped with a passive cooling system that brings its temperature down to about -230°C by radiating heat into space. Three active coolers take over from there, and bring the temperature down further to an amazing low of -273.05°C, only 0.1°C above absolute zero – the coldest temperature theoretically possible in our Universe.

Such low temperatures are necessary for Planck’s detectors to study the Cosmic Microwave Background (CMB), the first light released by the universe only 380 000 yrs after the Big Bang, by measuring its temperature across the sky.

All sky image

This week on 5 July 2010, the Planck mission delivered its first all-sky image. It not only provides new insight into the way stars and galaxies form but also tells us how the Universe itself came to life after the Big Bang.

“This is the moment that Planck was conceived for,” says ESA Director of Science and Robotic Exploration, David Southwood. “We’re not giving the answer. We are opening the door to an Eldorado where scientists can seek the nuggets that will lead to deeper understanding of how our Universe came to be and how it works now. The image itself and its remarkable quality is a tribute to the engineers who built and have operated Planck. Now the scientific harvest must begin.”

From the closest portions of the Milky Way to the furthest reaches of space and time, the new all-sky Planck image is an extraordinary treasure chest of new data for astronomers.

The main disc of our Galaxy runs across the centre of the image. Immediately striking are the streamers of cold dust reaching above and below the Milky Way. This galactic web is where new stars are being formed, and Planck has found many locations where individual stars are edging toward birth or just beginning their cycle of development.

Less spectacular but perhaps more intriguing is the mottled backdrop at the top and bottom. This is the ‘cosmic microwave background radiation’ (CMBR). It is the oldest light in the Universe, the remains of the fireball out of which our Universe sprang into existence 13.7 billion years ago.

While the Milky Way shows us what the local Universe looks like now, those microwaves show us what the Universe looked like close to its time of creation, before there were stars or galaxies. Here we come to the heart of Planck’s mission to decode what happened in that primordial Universe from the pattern of the mottled backdrop.

The microwave pattern is the cosmic blueprint from which today’s clusters and superclusters of galaxies were built. The different colours represent minute differences in the temperature and density of matter across the sky. Somehow these small irregularities evolved into denser regions that became the galaxies of today.

A Clockwork Universe
The picture of the universe we have now is avery different one from the early days of modern science, when clocks and clockwork were one of the leading technologies. The Clockwork Universe Theory was a theory, established by Isaac Newton, as to the origins of the universe in this. age when clocks were an important technology in an age when machines would soon create a new industrial world.

A “clockwork universe” can be thought of as being a clock wound up by God and ticking along, as a perfect machine, with its gears governed by the laws of physics. What sets this theory apart from others is the idea that God’s only contribution to the universe was to set everything in motion, and from there the laws of science took hold and have governed every sequence of events since that time.

This idea was very popular among deists during the Enlightenment, when scientists realized that Newton’s laws of motion, including the law of universal gravitation, could explain the behavior of the solar system.

However Newton excludes the idea of free will from this world of mechanical motions, since if people believed that all things have already been set in motion and are just parts of a predictable machine, then, Newton feared, the idea of everything being predetermined would lead people to not believing in a God any more.

Isaac Newton’s conception of the universe was one huge, regulated and uniform machine that operated according to natural laws in absolute time, space, and motion. In this new world that Newton created, God was the master-builder, who created the perfect machine and let it run. God was the Prime Mover, who brought into being the world in its lawfulness, regularity, and beauty. This view of God as the creator, who stood aside from his work and didn’t get involved directly with humanity was called Deism and was accepted by many who supported the “new philosophy”.

A similar concept goes back, at least, to John of Sacrobosco‘s early 13th century introduction to astronomy: On the Sphere. Johannes de Sacrobosco or Sacro Bosco (John of Holywood, c. 1195 – c. 1256 AD) was a scholar, monk, and astronomer (probably English, but possibly Irish or Scottish} who taught at the University of Paris and wrote the authoritative mediaeval astronomy text Tractatus de Sphaera.

Sacrobosco spoke of the universe as the machina mundi, the machine of the world, suggesting that the reported eclipse of the Sun at the crucifixion of Jesus was a disturbance of the order of that machine.

These days we can see that this theory was very much an idea of those times. Modern physics undermines this theory with the second law of thermodynamics ( the total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value) and quantum physics with its unpredictable random behavior.

An orrery is a mechanical device that illustrates the relative positions and motions of the planets and moons in the solar system in a heliocentric model. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.

Our summer almanac 25.06.2010 – 01.07.2010

Posted in astronomical time on July 2, 2010 by espacelab

Knowing where we are and what the time is
In the constellation Gemini the star known as Pollux, named after one of the twin sons of Zeus, is No 21 among the “navigational stars”. Telling the time and finding out where we are connected in the first clock faces, based as they are on the astrolabe, an instrument that can be used to work out our latitude position by measuring the angles of sun, moon and stars.

Astroclocks and Astrolabes
The first mechanical astronomical clocks were influenced by the astrolabe; in many ways they could be seen as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. For example, Richard of Wallingford’s clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.

Many astronomical clocks, such as the famous clock at Prague, use an astrolabe-style display.

Celestial Spheres
The design of astrolabes, and the first astronomical clocks, are made up the many rings that show the movements in the heavens. In Greek antiquity the ideas of celestial spheres and rings first appeared in the cosmology of Anaximander in the early 6th century BC. Following Anaximander, his pupil Anaximenes (c. 585–528/4) held that the stars, sun, moon and the planets are all made of fire. He thought the stars are fastened on a revolving crystal sphere, the but the sun, moon and planets, and also the Earth, all just ride on air like leaves because of their breadth. After Anaximenes, Pythagoras, Xenophanes and Parmenides all held that the universe was spherical. And much later in the fourth century BC Plato’s Timaeus proposed that the body of the cosmos was made in the most perfect and uniform shape, that of a sphere containing the fixed stars. So the celestial spheres, or celestial orbs, became the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, and others. In these celestial models the stars and planets are carried around by being embedded in rotating spheres made of an aetherial transparent fifth element (quintessence), like jewels set in orbs.

The astronomer Ptolemy (fl. ca. 150 AD) defined geometrical predictive models of the motions of the stars and planets in his Almagest and extended them to a unified physical model of the cosmos in his Planetary hypotheses.

In the middle ages in Europe the ideas went back to the idea that the Earth was the centre of the universe. Medieval Christians identified the sphere of stars with the Biblical firmament and sometimes posited an invisible layer of water above the firmament, to accord with Genesis.

Around a thousand years ago, the Arabic astronomer and polymath Ibn al-Haytham (Alhacen) developed the idea of Ptolemy’s geocentric epicyclic models as being like nested spheres. In chapters 15-16 of his Book of Optics, Ibn al-Haytham also discovered that the celestial spheres do not consist of solid matter.

The Earth orbits the Sun
We take our modern knowledge for granted, and yet it isn’t hard to imagine believing the world is in fact a flat disc, and that the sun rises over this disc and sets beneath it. And even if people knew for certain that the Earth was a sphere, it isn’t hard to understand how people might think that the Earth was at the centre of the Universe.

The name of Nicolaus Copernicus Warmiensis, called Copernicus, is synonymous with a cosmological revolution. Mikolaj Kopernik, as he is known in Poland, spent much of his life from 1506 making observations of the stars and the planets, using relatively simple astronomical instruments.

By 1512, while still making observations from the tower in which he lived, set in the thick defensive walls of Frauenburg cathedral (today Frauenburg is known as the city of Frombork) he had begun to develop a new theory about the movements of the planets. In 1530 he published a book called De Revolutionibus Orbium Coelestium, which explained that it was possible to calculate that the Earth was not at the centre of the universe, but like the other planets, the Earth went around the Sun.

This theory challenged all those ideas about the way universe worked that were handed down over the centuries by people from ancient times. Plato (ca.428 BC-ca.348 BC) believed that the stars were living beings, eternal and divine. He thought that the motions of these heavenly bodies must be perfectly circular, as such a perfect and beautiful geometrical form as the circle would be a natural form for heavenly things.

According to Aristotle (384 BC-322 BC), the Earth was spherical, and remained quite still at the centre of the universe. He thought that the boundary of the universe was a sphere of fixed stars, and that between this sphere and the Earth there were a series of 55 spherical shells made of a heavenly element called aether. This aether was invisible and weightless, and purer than fire. The planets, the Sun and the Moon were part of these aetherial shells, with the Moon being the shell-like sphere closest to Earth.

Nowadays we know that though the stars may look fixed in the sky and frozen in time, they are in fact in movement. If we could speed up time we would see all stars move, while the planets would each be a speeding blur. The stars would all move in different directions and at different speeds.

Clocks, chronometers, longitude and knowing where we are
A marine chronometer is a clock which is precise enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation.

Longitude is given as an angular measurement ranging from at the Prime Meridian to +180° eastward and −180° westward. The Greek letter λ is used to denote the location of a place on Earth east or west of the Prime Meridian.

Maps and longitude
Longitude is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement. Constant longitude is represented by lines running from north to south. The line of longitude (meridian) that passes through the Royal Observatory, Greenwich, in England, establishes the meaning of zero degrees of longitude, or the Prime Meridian.

This map of Basingstoke is framed by a rectangle that shows along each of the sides the position of the latitude grid, and along the top and bottom the longitude positions.

Degrees and minutes
Each degree of longitude is sub-divided into 60 minutes, each of which divided into 60 seconds. Basingstoke is west of the Greenwich Meridian by 1 degree and 6 seconds of longitude. So maps are divided spatially into degrees, minutes and seconds, as clocks are divided into hours, minutes and seconds.

Latitude and longitude
A location’s position along a meridian is given by its latitude, which is identified by the north-south angle between the local vertical and the plane of the Equator. Unlike latitude, which has the equator as a natural starting position, there is no natural starting position for longitude. Therefore, a reference meridian had to be chosen. It was a popular practice to use a nation’s capital as the starting point, but other significant locations were also used. While British cartographers had long used the Greenwich meridian in London, other references were used elsewhere, including: El Hierro, Rome, Copenhagen, Jerusalem, Saint Petersburg, Pisa, Paris, Philadelphia, and Washington. In 1884, the International Meridian Conference adopted the Greenwich meridian as the universal Prime Meridian or zero point of longitude.

The importance of the measurement of longitude is vital, both to cartography and to provide safe ocean navigation. Mariners and explorers for most of history struggled to determine precise longitude. Finding a method of determining exact longitude took centuries, resulting in the history of longitude recording the effort of some of the greatest scientific minds.

Latitude was calculated by observing with quadrant or astrolabe the inclination of the sun or of charted stars, but longitude presented no such manifest means of study. Amerigo Vespucci was perhaps the first to proffer a solution, after devoting a great deal of time and energy studying the problem during his sojourns in the New World:

As to longitude, I declare that I found so much difficulty in determining it that I was put to great pains to ascertain the east-west distance I had covered. The final result of my labours was that I found nothing better to do than to watch for and take observations at night of the conjunction of one planet with another, and especially of the conjunction of the moon with the other planets, because the moon is swifter in her course than any other planet. I compared my observations with an almanac. After I had made experiments many nights, one night, the twenty-third of August, 1499, there was a conjunction of the moon with Mars, which according to the almanac was to occur at midnight or a half hour before. I found that…at midnight Mars’s position was three and a half degrees to the east.

By comparing the relative positions of the moon and Mars with their anticipated positions, Vespucci was able to crudely deduce his longitude. But this method had several limitations: First, it required the occurrence of a specific astronomical event (in this case, Mars passing through the same right ascension as the moon), and the observer needed to anticipate this event via an astronomical almanac. One needed also to know the precise time, which was difficult to ascertain in foreign lands. Finally, it required a stable viewing platform, rendering the technique useless on the rolling deck of a ship at sea.

In 1612, Galileo Galilei proposed that with sufficiently accurate knowledge of the orbits of the moons of Jupiter one could use their positions as a universal clock and this would make possible the determination of longitude, but the practical problems of the method he devised were severe and it was never used at sea. In 1714, motivated by a number of maritime disasters attributable to serious errors in reckoning position at sea, the British government established the Board of Longitude: prizes were to be awarded to the first person to demonstrate a practical method for determining the longitude of a ship at sea. These prizes motivated many to search for a solution.

John Harrison, a self-educated English clockmaker then invented the marine chronometer, a key piece in solving the problem of accurately establishing longitude at sea, thus revolutionising and extending the possibility of safe long distance sea travel.

The first true chronometer was the life work of this one man spanning 31 years of persistent trial and error that revolutionized maritime navigation. Though the British rewarded John Harrison for his marine chronometer in 1773, chronometers remained very expensive and the lunar distance method continued to be used for decades. Finally, the combination of the availability of marine chronometers and wireless telegraph time signals put an end to the use of lunars in the 20th century.

Near Castle Hill School 01.07.2010