The Earth in
its orbit around theSun causes
the Sun to appear on the celestial sphere moving over theecliptic (red),
which is tilted with respect to the equator (blue-white).
In both astrology and
historical astronomy, the zodiac (Greek:
ζῳδιακός, zōidiakos) is a
circle of twelve 30° divisions of celestial longitude that are centered upon
the ecliptic:
the apparent path of the Sun across
the celestial sphere over the course of the
year. The paths of the Moon and
visible planets also
remain close to the ecliptic, within the belt of the zodiac, which extends 8-9°
north or south of the ecliptic, as measured in celestial latitude. Because the divisions are
regular, they do not correspond exactly to the twelveconstellations after
which they are named.
The Axis advance was stopped in 1942 when
Japan lost a critical Battle of Midway,
near Hawaii,
and Germany was defeated inNorth Africa and then, decisively, at Stalingrad in the Soviet Union. In 1943,
with a series of German defeats on the Eastern Front, the Allied invasion of Italy which
brought about that nation's surrender, and Allied victories in the Pacific, the
Axis lost the initiative and undertook strategic retreat on all fronts. In
1944, the Western Allies invaded France,
while the Soviet Union regained all of its territorial losses and invaded
Germany and its allies. During 1944 and 1945 the Japanese began suffering major
reverses in mainland Asia in SouthCentral China and Burma,
while the Allies defeated the Japanese Navy and captured key Western
Pacific islands.
World War II altered the political
alignment and social structure of the world. The United Nations (UN)
was established to foster international co-operation and prevent future
conflicts. The great powers that were the victors of the war—the United
States, the Soviet Union, China, the United Kingdom, and France—became the permanent
members of the United Nations Security Council.[3] The
Soviet Union and the United States emerged as rival superpowers,
setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the
influence of European great powers started to decline, while thedecolonisation of Asia and Africa began. Most countries whose
industries had been damaged moved towards economic recovery.
Political integration, especially in Europe, emerged as an effort to stabilise
postwar relations and co-operate more effectively in the Cold War.[4]
Dynamite is an explosive material based on nitroglycerin,
using diatomaceous earth (AmE:
kieselgur; BrE: kieselguhr), or another absorbent
substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using
organic materials such as sawdust are less stable and such use has been
generally discontinued. Dynamite was invented by the Swedish chemist
and engineer Alfred Nobel in Geesthacht,
Germany, and patented in 1867. Its name was coined by Nobel from the Ancient Greek word
δύναμιςdýnamis,
meaning "power".
Dynamite is a high explosive,
which means its power comes from detonation rather
than deflagration. Dynamite is mainly used in the mining,quarrying, construction,
and demolition industries,
and it has had some historical usage in warfare. However the unstable nature of
nitroglycerin, especially if subjected to freezing, has rendered it obsolete
for military uses. Popular familiarity with dynamite led tometaphoric uses,
such as saying that a particular issue is "political dynamite".
Dynamite consists of three parts nitroglycerin,
one part diatomaceous earth and a small admixture of sodium carbonate.
This mixture is formed into short sticks and wrapped in paper. A blasting cap
and fuse of any length are then inserted down the middle. Nitroglycerin by
itself is a very strong explosive, and in its pure form it is extremely
shock-sensitive (that is, physical shock can cause it to explode), and degrades
over time to even more unstable forms. This makes it highly dangerous to
transport or use in its pure form.
Absorbed into diatomaceous earth or
sawdust, nitroglycerin is less shock-sensitive. Over time, the dynamite will
"weep" or "sweat" its nitroglycerin, which can then pool in
the bottom of the box or storage area. (For that reason, explosive manuals recommend
the repeated turning over of boxes of dynamite in storage.) Modern packaging
helps eliminate this by placing the dynamite into sealed plastic bags, and
using wax coated cardboard. Crystals will form on the outside of the sticks
causing them to be even more shock, friction or temperature sensitive. This
creates a very dangerous situation. While the risk of an explosion without the
use of a blasting cap is minimal for fresh
dynamite, old dynamite is dangerous.
Dynamite is usually sold in the form of
cylinders about 8 in (20 cm) long and about 1.25 in
(3.2 cm) in diameter, with a weight of about 0.5 lb troy
(0.186 kg). Other sizes also exist. The maximum shelf life of
nitroglycerin-based dynamite is recommended as one year from the date of
manufacture under good storage conditions. Another form of dynamite consists of
nitroglycerin dissolved in nitrocellulose and
a small amount of ketone. This form of dynamite is similar to cordite and gelignite,
and is much safer than the simple mix of nitroglycerin and diatomaceous earth. Military
dynamite achieves greater stability by avoiding the use of
nitroglycerin and uses much more stable chemicals.
Newton's Principia formulated the laws of motion and universal gravitation, which dominated
scientists' view of the physical universe for the next three centuries. By
deriving Kepler'slaws of planetary motion from his
mathematical description of gravity, and then using the same principles to
account for the trajectories of comets, the tides, the precession of the equinoxes,
and other phenomena, Newton removed the last doubts about the validity of the heliocentric model of
the cosmos. This work also demonstrated that themotion of
objects on Earth and of celestial bodies
could be described by the same principles. His prediction that the Earth should
be shaped as an oblate
spheroid was later vindicated by the measurements of Maupertuis, La Condamine,
and others, which helped convince most Continental
European scientists of the superiority of Newtonian mechanics
over the earlier system of Descartes.
Newton was a fellow of Trinity
College and the second Lucasian Professor of Mathematics at
the University of
Cambridge. He was a devout but unorthodox Christian and, unusually
for a member of the Cambridge faculty of the day, he refused to take holy orders in the Church of England, perhaps
because he privately rejected the doctrine of the Trinity. Beyond his work
on the mathematical sciences, Newton dedicated much of his time to the study of biblical
chronology and alchemy, but most of his
work in those areas remained unpublished until long after his death. In his
later life, Newton became president of the Royal Society. He also
served the British government as Warden and Master of the Royal Mint.
