Tuesday, 07 October 2003
Pix Of The Day: Mirthful Menhir Merits Mention
CREDITS: © Peter Turner/MaccCAM.co.uk MAP: Morlaix
When clicked, thumbnails popup enlarged versions of the images.
Any photo web page containing a picture of a 4,600 year old tumulus gets our attention. If it also contains a picture of a menhir, showing the fingerprints of the giant hand that thrust it into the earth, then that rates an entry here on ODAAT. These delights are from Peter Turner's MaccCAM.co.uk on a continuing French vacation in the Brittany region; and the lovely Nic has been revealed for the first time!
Earlier, we featured a picture of Roscoff from the MaccCAM archives, in an item on the 'Onion Johnnies', and we now recommend a visit to all three available galleries:  Departure;  Roscoff; and  Morlaix. The galleries contain interesting images, selected by the eye of a thoughtful traveller, with special attention to architectural features. Todays picture shows a view of the Morlaix River, taken as the party moved eastwards to relocate near the Mont St. Michel. A continuation gallery is promised, so we expect to feature another picture from this collection in the near future. From our own memories of visits to the 'Marvel of the West', we look forward to seeing which architectural features attracted Peter.
On This Day In 2002: Chandra and the Crab Nebula - Mon, 07 Oct 2002
CREDITS: X-ray & optical images: © NASA/CXC/ASU/J. Hester et al.
NASA Chandra X-ray Observatory Center (CXC) - Crab Nebula page.
This picture is a composite image of the Crab Nebula, showing the X-ray (blue), and optical (red) images superimposed, taken on 6 April 2001. The size of the X-ray image is smaller because the higher energy X-ray emitting electrons radiate away their energy more quickly than the lower energy optically emitting electrons as they move. The inner ring is about one light year across. There is a hi-res version for visitors with larger monitors. For full details on this, and other projects, a CXC site visit is recommended: the navigation is very well done, the images are superb, and everything is clearly explained for lay people. There are excellent project and educator resources.
The Crab Nebula is the remnant of a star that was observed to explode in 1054 A.D. It is located 6,000 light years away in the constellation of Taurus, and is a strong emission source, in wavelengths from radio through to gamma rays. The remnant center of the explosion contains a rapidly rotating neutron star - or pulsar - that is apparently pumping enormous amounts of energy into the nebula in the form of high-energy particles and magnetic fields. Chandra's X-ray image provides significant clues to the workings of this mighty cosmic generator, which is producing energy at the rate of 100,000 suns. The dramatic tilted rings that span the distance of a light year appear to have been flung outward from the pulsar. Perpendicular to the rings, jet-like structures produced by high-energy particles blast away from the pulsar.
A neutron star is formed by the extreme conditions created in a supernova. When a massive star explodes, most of the star is flung into space, but the core of the star is compressed to form a rapidly rotating dense ball of neutrons; 30 revolutions per second, and twelve miles in diameter in the case of the Crab Nebula. The collapse and rapid rotation of the neutron star cause it to become highly magnetized. Such highly magnetized, rapidly rotating neutron stars as the Crab pulsar, can produce electricity at ten quadrillion volts.
Neutron star gravity, which is more than a hundred billion times stronger than gravity on Earth, is overwhelmed by the electric field and particles are pulled off the neutron star and accelerated to speeds near the speed of light. A blizzard of electrons and anti-matter electrons, or positrons, is produced by these particles. The pulsed emission from the Crab Nebula, observed at all wavelengths from radio through gamma rays, is thought to be caused by this process.
As particles stream out from the pulsar and spiral around magnetic field lines, they produce a distinctive kind of radiation known as synchrotron radiation. The Crab Nebula's bell-shape in the X-ray image is due to synchrotron radiation from a huge magnetized bubble of high-energy electrons several light years in diameter.
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Jules Laforgue (1860-1887)
"Ah! que la vie est quotidienne."
Oh, what a day-to-day business life is.
'Complainte sur certains ennuis' (1885)