Our summer almanac 10.09.2010 – 16.09.2010

Eid celebrations in Trafalgar Square in London

September 10 is Eid-Ul-Fitr
The Eid occurs at the end of Ramadan when Muslims celebrate the end of fasting and thank Allah for His help with their month-long act of self-control. Eid ul-Fitr (Arabic: عيد الفطر ‘Īdu l-Fiṭr‎), often abbreviated to Eid, is a three-day Muslim holiday that marks the end of Ramadan, the Islamic holy month of fasting (sawm). Eid is an Arabic word meaning “festivity”, while Fiṭr means “conclusion of the fast”; and so the holiday celebrates the conclusion of the thirty days of dawn-to-sunset fasting during the entire month of Ramadan. The first day of Eid, therefore, falls on the first day of the month Shawwal.

It is said that the sacred knowledge was revealed to Muhammad during the month of Ramadan. As a mark of respect to Allah and to show gratitude to him for the true knowledge that he gifted to his sons and daughters, the prophet asked his followers (and therefore the followers of Islam) to pass the month of Ramadan in fasting, prayers and other austerities and end the month-long non-indulgence with festive celebrations. This is how Eid-Ul-Fitr was born. This three-day long celebration ends the ninth month and begins the tenth month of Shawwal with absolute happiness and contentment for the ability to sacrifice for Allah. The aim of this festival is to promote peace, strengthen the feeling of brotherhood and bring oneself back to the normal course of life after a month-long period of self-denial and religious devotion.

Muslims are not only celebrating the end of fasting, but thanking Allah for the help and strength that he gave them throughout the previous month to help them practise self-control.

The festival begins when the first sight of the new moon is seen in the sky. Muslims in most countries rely on news of an official sighting, rather than looking at the sky themselves.

The celebratory atmosphere is increased by everyone wearing best or new clothes, and decorating their homes. There are special services out of doors and in Mosques, processions through the streets, and of course, a special celebratory meal – eaten during daytime, the first daytime meal Muslims will have had in a month. Eid is also a time of forgiveness, and making amends.

Solar spectacular

This week NASA’s Solar Dynamics Observatory watched as an active region in the Sun’s southern hemisphere produced a whole series of looping arcs of plasma in profile (Sept. 11-13, 2010). The arcs are actually charged particles spiraling along magnetic field lines. The images were taken in extreme ultraviolet light and reveal the dynamic activity visible above active regions. The material seen here is ionized iron heated to about one million degrees.

Black Holes
The X-ray star called Cygnus X-1 in the part of the sky where you can see Cygnus the Swan, is a black hole.

As far as we know, the first person to suggest that there were ‘dark stars’ that are impossible to see, was an English parson living in the eighteenth-century called John Michell. While rector of a parish in Yorkshire he published a number of extraordinary astronomical papers.

In 1783 Michell’s friend Henry Cavendish read one of his papers to the Royal Society that said that “If there should really exist in nature any bodies whose density is not less than the Sun, and whose diameters are more than 500 times the Sun, since their light could not arrive at us we could have no information from sight; yet, if any other luminiferous bodies should happen to revolve around them we might still perhaps from the motions of these revolving bodies infer the existence of the central ones”. These dark stars are the kind of black holes that are associated with what are called quasi-stellar radio sources, or ‘quasars’ for short.

John Wheeler was responsible for giving black holes their modern name in 1967, just after the discovery of ‘pulsars’, but it was Karl Schwarzschild who predicted their existence in 1916. Albert Einstein studied the idea and developed a mathematical description of black holes in the 1930’s. At the end of the 1930’s, Robert Oppenheimer and George Volkhoff pointed out that the equations that say neutron stars exist also put an upper limit to the amount of mass a neutron star can have, at about three times the mass of our Sun. Any bigger than this and a collapsing star would shrink down indefinitely towards a single point. This single point is called a ‘singularity’.

A collapsing object of this type would disappear to become a dark star because the gravitational pull at its surface is so immense that light itself is unable to escape into space as radiation. This brings us back to Cygnus X-1 and how astronomers pinpointed its radio signals in the 1970’s using a satellite called Uhuru. When Cygnus X-1 was identified by astronomers studying this source of X-rays using optical telescopes, it became clear that the X-rays were coming not from a blue star called HDE 226868, but from a point nearby. The star and the X-ray source orbit around each other once every 5.6 days. The mass of the object in orbit around the visible star has been calculated at 20 times the mass of the Sun, which means that if it was an ordinary star it would be bright enough to be visible, and too big to be a white dwarf or neutron star, so it must be a black hole!

There are a few more dead and dying stars like this that have been discovered recently. They are called ‘stellar mass black holes’ because they have masses similar to stars.


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