Our summer almanac 30.07.2010 – 05.08.2010

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.


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