(1) (4) (1) (2) (3) (4) Hubble

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1 1) 2) 3) 4) 5)

2 (1) (4) Our modern picture of the universe dates back only to 1924, when the American astronomer Edwin Hubble demonstrated that the Milky Way was not the only galaxy. He found, in fact, many others, with vast tracts of empty space between them. In order to prove this, Hubble needed to determine the distances from the earth to the other galaxies. But these galaxies were so far away that, unlike nearby stars, their positions really do appear fixed. Since Hubble couldn't use the parallax on these galaxies, he was forced to use indirect methods to measure their distances. One obvious measure of a star's distance is its brightness. But the apparent brightness of a star depends not only on its distance but also on how much light it radiates (its luminosity). A dim star, if near enough, will outshine the brightest star in any distant galaxy. So in order to use apparent brightness as a measure of its distance, we must know a star's luminosity. The luminosity of nearby stars can be calculated from their apparent brightness because their parallax enables us to know their distance. Hubble noted that these nearby stars could be classified into certain types by the kind of light they give off. The same type of stars always had the same luminosity. He then argued that if we found these types of stars in a distant galaxy, we could assume that they had the same luminosity as the similar stars nearby. With that information, we could calculate the distance to that galaxy. If we could do this for a number of stars in the same galaxy and our calculations always gave the same distance, we could be fairly confident of our estimate. In this way, Hubble worked out the distances to nine different galaxies. Today we know that stars visible to the naked eye make up only a minute fraction of all the stars. We can see about five thousand stars, only about percent of all the stars in just our own galaxy, the Milky Way. The Milky Way itself is but one of more than a hundred billion galaxies that can be seen using modern telescopes and each galaxy contains on average some one hundred billion stars. parallax: apparent: luminosity: (1) (2) (3) (4) Hubble

3 (1) (3) Whilst we focus on the chemical uses of solvents, it should not be forgotten that, of an estimated 60 million tones of synthetic solvents used each year, a large proportion is used for non-chemical applications. Vapour degreasing, dry cleaning and immersion cleaning of mechanical parts are amongst the largest of these. Despise their evident utility, the use of solvents in chemical processes must be scrutinized from environmental and economic points of view because solvent use is inherently wasteful. In a chemical process, a solvent is usually added to reactants to facilitate reaction, and is later removed from the chemical product prior to disposal or, preferably, recycling and reuse. Removal of residual solvent from a chemical product is frequently achieved either by evaporation or distillation, and for this reason most popular solvents are highly volatile. This volatility has led to some major public concerns about solvent use. Leaks and spillage of volatile solvents inevitably lead to evaporation into the atmosphere. Atmospheric pollution has been one of the major global environmental issues of the late 20th and early 21st century, and emissions of some categories of volatile organic solvents have been implicated in the depletion of the Earth's ozone layer and in the greenhouse effect. On a local level, exposure to volatile organic compounds (VOCs) in the workplace may lead to dizziness, nausea and other, longer term effects including respiratory problems and cancer. solvent: degreasing: immersion: evaporation: distillation: dizziness: nausea: respiratory: (1) (2) (3)

4 (A) (B) (A) (1) (3) The Cambridge theoretical physicist Paul Adrien Maurice Dirac ( ) was engaged in the late 1920s in developing a version of quantum mechanics that would be consistent with special relativity. In the course of this work, he encountered the surprising result that the equation he had worked out to describe a single electron had solutions of negative energy. To explain why there is not a catastrophic collapse of all electrons into these negative energy states, he proposed in 1930 that the states of negative energy are normally already filled, and are thereby unable to accept additional electrons by the same rule (known as the Pauli exclusion principle) that keeps the outer electrons in an atom from falling into the inner orbits of lower energy. A few negative energy states might be unoccupied, and these holes in the sea of negatively charged particles with negative energy would appear as particles of positive energy and positive charge. Under the influence of what seems to have been a general code of scientific behavior that proposing new particles was somehow not respectable Dirac at first thought that these holes were to be identified with protons. However, Hermann Weyl pointed out that there was a symmetry between holes and electrons, and Dirac was forced to conclude that the holes would have to carry precisely the same mass as electrons. This prediction was unexpectedly verified in 1932 when the American experimentalist Carl Anderson ( ) observed tracks of cosmic-ray particles that curved in a magnetic field about as much as electron tracks, but in the opposite direction. These particles, called positrons, are now known with great precision to have the same mass as electrons and the opposite electric charge. (1) (2) Dirac (hole) (3) Anderson (B) (1) (2) (1) (2) m F W l

5 (1) (4) Carbon dioxide from burning fossil fuels is dramatically altering ocean chemistry and threatening marine life. It warns that marine organisms that secrete skeletal structures, such as corals and pteropods, may be profoundly affected by the rising acidification of surface ocean waters This added CO 2 has already increased the hydrogen ion concentration of the surface ocean by 30% and is predicted to increase it 150% relative to the preindustrial level by As the acidity rises, the availability of carbonate in the ocean decreases. By 2100, the calcification rates for coral and other creatures that build skeletons from calcium carbonate will decrease by up to 60%. "It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life," says Joan Kleypas. "It is vital to develop research strategies to better understand the long-term vulnerabilities of sensitive marine organisms to these changes." Many lab studies show that coral calcification decreases as the oceans become more acidic, threatening reef structures. This threat is hitting coral reefs at the same time that they are being hit by warming-induced mass bleaching events--the bleaching caused by warmer ocean temperatures. Lab studies confirm that marine plankton, such as pteropods, are affected by declining concentrations of carbonate ion. Shelled pteropods are an important food source for salmon, mackerel, and cod. "Decreased calcification in marine algae and animals is likely to impact marine food webs and has the potential to substantially alter the productivity of the ocean," says Victoria J. Fabry. secrete: skeletal structure: coral: pteropod: calcification: vulnerability: algae: (1) (2) (3) CO 2 (4)