OZONE LAYER

The ozone layer is a deep layer in the stratosphere, encircling the Earth, that has large amounts of ozone in it. The layer shields the entire Earth from much of the harmful ultraviolet radiation that comes from the sun.

Interestingly, it is also this ultraviolet radiation that forms the ozone in the first place. Ozone is a special form of oxygen, made up of three oxygen atoms rather than the usual two oxygen atoms. It usually forms when some type of radiation or electrical discharge separates the two atoms in an oxygen molecule (O2), which can then individually recombine with other oxygen molecules to form ozone (O3).

The ozone layer became more widely appreciated by the public when it was realized that certain chemicals mankind manufactures, called chloroflurocarbons, find their way up into the stratosphere where, through a complex series of chemical reactions, they destroy some of the ozone. As a result of this discovery, an international treaty was signed in 1973 called the Montreal Protocol, and the manufacture of these chemicals was greatly reduced.

The ozone layer has since begun to recover somewhat as a result of these efforts, but there is some science which now suggests that the major volcanic eruptions (mainly El Chichon in 1983 and and Mt. Pinatubo in 1991) which have occurred since we started monitoring ozone with satellites in the late 1970's, could have also contributed to the ozone depletion.

While stratospheric ozone, which protects us from the sun, is good, there is also ozone produced near the ground, from sunlight interacting with atmospheric pollution in cities, that is bad. It causes breathing problems for some people, and usually occurs in the summertime when the pollution over a city builds up during stagnant air conditions associated with high pressure areas.

LIGHT YEAR
A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000 kilometers.

Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance


ASTRONOMICAL UNIT

150 million kilometers/93 million miles

An Astronomical unit is the standard distance between the earth and the sun.

It is about 149,597,870.691 kilometers (92,955,807.267 miles).

It is defined as the distance that an object would have a perfectly circular orbit of exactly 365.2568983 days (31,558,196.01312 seconds).


PARSEC
A parsec is an astronomical unit of measurement that is equivalent to 3.26 light years distance, or the distance photons will travel in vacuum over the period of 3.26 years. Light travels at an approximate speed of 186,000 miles per second (300,000 kilometers per second), so a parsec represents a distance of just over 19 trillion miles (~31 trillion kilometers).

By comparison, the average distance to the Sun from Earth is only 93 million miles (150,000,000 km). This distance is referred to as one astronomical unit (AU). One would have to make 103,000 round trips to the Sun to cover the distance indicated by a single parsec (206,265 AUs = 1 parsec). Our solar system, defined for example by Pluto's orbit, is only 1/800ths of a light year across. It would have to be 2,608 times larger to equal 1 parsec across.


PARALLAX

Parallax causes adjacent pictures for a panorama to differ in ways that prevents them from being stitched together perfectly. It can cause ghosting, blurring, or even prevent stitching software from being able to work out where to position the pictures to be able to stitch them together.

It's really easy to see the effect of parallax: Hold up your index finger in front of you. Close one eye and line up your finger with something further away such as a door, piece of furniture, window, whatever. Now without moving your finger, rotate your head from left to right - your finger will seem to move slightly as you turn your head. Voilà! you are seeing parallax.

Exactly the same happens when you shoot pictures with your camera

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MERCURY THEROMETER
thermometer consisting of mercury contained in a bulb at the bottom of a graduated sealed glass capillary tube marked in degrees Celsius or Fahrenheit; mercury expands with a rise in temperature causing a thin thread of mercury to rise in the tube.


ALCOHOL THERMOMETER
An alcohol thermometer is a temperature measuring equipment that is made up of a glass capillary tube that is marked with Celsius or Fahrenheit degrees symbols and contains alcohol that rises when it expands or falls when it contracts due to the change in temperature. Alcohol thermometers are also known as spirit thermometers.

Alcohol thermometer is mainly used as a substitute for the mercury-in-glass thermometer since these two types of thermometers works in a same way. A mercury-in-glass thermometer is a thermometer that has mercury in its glass tube. What you can see in an alcohol thermometer is an organic liquid which is seen in a glass bulb that is connected to a capillary of the same glass whereby the end is closed with an expansion bulb. The organic liquid in the alcohol thermometer can be pure ethanol, toluene, kerosene or Isoamyl acetate. The types of organic liquid used in an alcohol thermometer will depend on the manufacturer and the working temperature range.


BIMETALLIC THEROMETER
The bimetallic thermometer consists of a bimetallic strip. A bimetallic strip is made of two thin strips of metals which have different coeffcients of expansion. The two metal strips are joined together by brazing, welding or reveting so that the relative motion between them is arrested.

The bimetallic strip is in the form of a cantilever beam. An increase in temperature will result in the deflection of the free end of the strip as shown i diagram. This deflection is linear and can be related to temperature changes.

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