A Solar Eclipse

A solar eclipse is a type of eclipse that occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks ("occults") the Sun. This can happen only at new moon, when the Sun and the Moon are inconjunction as seen from Earth in an alignment referred to as syzygy. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses only part of the Sun is obscured.

If the Moon were in a perfectly circular orbit, a little closer to the Earth, and in the same orbital plane, there would be total solar eclipses every single month. However, the Moon's orbit is inclined (tilted) at more than 5 degrees to Earth's orbit around the Sun (see ecliptic) so its shadow at new moon usually misses Earth.

Earth's orbit is called the ecliptic plane as the Moon's orbit must cross this plane in order for an eclipse (both solar as well as lunar) to occur. In addition, the Moon's actual orbit is elliptical, often taking it far enough away from Earth that its apparent size is not large enough to block the Sun totally. The orbital planes cross each year at a line of nodes resulting in at least two, and up to five, solar eclipses occurring each year; no more than two of which can be total eclipses.

However, total solar eclipses are rare at any particular location because totality exists only along a narrow path on Earth's surface traced by the Moon's shadow or umbra.

Special eye protection or indirect viewing techniques must be used when viewing a solar eclipse to avoid eye damage.

When at a spot from which a 'total eclipse' is visible, an observer can see a number of exciting effects.  One such effect occasionally seen is Baily's Beads where a sequence of spots of light appears along the edge of the Moon. This is caused by the sun shining through the valleys of the Moon's mountainous regions

The following table shows the upcoming total solar eclipses for the next few years:

Date	Region Visible
20 March 2015	North Atlantic regions, Faroe Islands and the North Pole
9 March 2016	Indonesia
21 August 2017	Parts of the mid- and west USA
2 July 2019	central Argentina, Chile, the Tuamotus (French Polynesia), parts of the South Pacific Ocean

For more information visit:- http://en.wikipedia.org/wiki/Solar_eclipse http://h2g2.com/approved_entry/A143812

How does a Laboratory Balance or Scale work?

There are two basic types of electronic balance designs.

1. Electromagnetic balancing type
2. Electrical resistance wire type (load cell type)

These are based on different principles, but both have neither directly measures mass. They measure the force that acts downward on the pan. This force is converted to an electrical signal and displayed on a digital display.
 

As a means of measuring force, the electromagnetic balance method uses the electromagnetic force generated from a magnet and coil, whereas the electrical resistance wire method uses the change in resistance value of a strain gauge attached to a piece of metal that bends in response to a force.
 

 
So why do electronic balances display mass values when that is not what they measure? It's because the reference standards for mass are weights, which are placed on a pan to inform the electronic balance that a given force is equivalent to a given number of grams, which is used for conversion. Consequently, electronic balances that do not perform this conversion accurately cannot display accurate mass values.

Readability and accuracy are not the same thing?

The readability of a balance is the smallest quantity that the balance will display. Accuracy is the difference between the known weight of a sample and the displayed weight. The accuracy of a balance can be measured only when the balance is in its operating environment

Location of the Balance

The precision and reproducibility of weighing results is closely associated with the location of the balance. To ensure that your balance can work under the best conditions, please observe the following guidelines:

Weighing bench

• Stable (lab bench, lab table, stone bench).  Your weighing bench should not sag when work is carried out on it and should transfer as few vibrations as possible.
• Antimagnetic (no steel plate).
• Protected against electrostatic charges (no plastic or glass).
• Wall or floor installation.  The weighing bench should be fixed either to the floor or on the wall.  Mounting the bench on both places at once transfers vibrations from wall and floor.
• Reserved for the balance.

The place of installation and the weighing bench must be stable enough that the balance display does not change when someone leans on the table or steps up to the weighing station. Do not use soft pads underneath, such as writing mats.  It is better to position the balance directly over the legs of the bench, since the area is subject to the fewest vibrations.

 

The article above is a very brief outline of laboratory balances or scales.  many factors affect the weighing accuracy besides location - eg temperature, humidity etc..Visit the last link below to download a complete guide to weighing.

For more information visit:-
http://www.shimadzu.com/an/hplc/support/lib/lctalk/66/66lab.html
http://electronics.howstuffworks.com/everyday-tech/digital-scale.htm
http://www.prlabs.co.uk/news/article.php?Id=140

Xenon

Xenon is a noble gas (or inert gas) with the symbol, Xe, and the atomic number, 54. Xenon is a clear and colourless, and odorless gas that is quite heavy. Xenon gas is 4.5 times heavier than Earth's atmosphere (which consists of a mixture of a number of gaseous elements and compounds). This element's mass comes from its nucleus, which contains 54 protons and a varying (but similar) number of neutrons. Xenon has 17 naturally-occurring isotopes (the most for any element), eight of which are stable, the most for any element, except tin, which has ten.

Xenon discharge tube

Tiny amounts of two xenon isotopes, xenon-133 and xenon-135, leak from nuclear reprocessing and power plants, but are released in higher amounts after a nuclear explosion of accident, such as what occurred at Fukushima. Thus, monitoring xenon's isotopes can ensure compliance with international nuclear test-ban treaties and also to detect whether rogue nations are testing their own nuclear weapons.

Xenon was discovered in England by the Scottish chemist William Ramsay and English chemist Morris Travers on July 12, 1898, shortly after their discovery of the elements krypton and neon. They found xenon in the residue left over from evaporating components of liquid air.

During the 1930s, American engineer Harold Edgerton began exploring strobe light technology for high speed photography. This led him to the invention of the xenon flash lamp, in which light is generated by sending a brief electrical current through a tube filled with xenon gas. In 1934, Edgerton was able to generate flashes as brief as one microsecond with this method.

Xenon as well as being used in flash lamps and arc lamps is also used as a general anaesthetic. Although it is expensive, anesthesia machines that can deliver xenon are about to appear on the European market, because advances in recovery and recycling of xenon have made it economically viable.

The first excimer laser design used a xenon dimer molecule (Xe2) as its lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is also being used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft.  It is also used in car headlights.

Xenon is obtained commercially as a byproduct of the separation of air into oxygen and nitrogen.
For more information visit:-
http://en.wikipedia.org/wiki/Xenon
http://www.theguardian.com/science/grrlscientist/2012/mar/16/1?guni=Article:in%20body%20link

The Fourth of July - Independence Day for America

Independence Day, commonly known as the Fourth of July, is a federal holiday in the United States commemorating the adoption of the Declaration of Independence on July 4, 1776, declaring independence from the Kingdom of Great Britain.

Independence Day is commonly associated with fireworks, parades, barbecues, carnivals, fairs, picnics, concerts, baseball games, family reunions, and political speeches and ceremonies, in addition to various other public and private events celebrating the history, government, and traditions of the United States. Independence Day is the National Day of the United States.

Also on this day of scientific note, Mars Pathfinder, an American spacecraft landed a base station with a roving probe on Mars on 4th July 1997. The mission carried a series of scientific instruments to analyse the Martian atmosphere, climate, geology and the composition of its rocks and soil.

On 4th July 2005,  The Deep Impact collider hits the comet Tempel 1 to analyse it's make up. And on 4th July 2012, the discovery of particles consistent with the Higgs boson at the Large Hadron Collider is announced at CERN.

All in all a day of many achievements in various scientific fields and another reason to celebrate.