Radio Astronomy

the recording and study of radio waves given out by many bodies in space including the Sun, stars and QUASARS.

Taken from Dictionary of Science

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Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. It differs from radar astronomy in that the latter utilizes artificial, rather than natural, radio sources. The initial detection of radio waves from an astronomical object (the Milky Way) was made in the 1930s, but subsequent advances (especially post-World War II) have identified a number of different sources of radio emission. These include stars and galaxies as well as entirely new classes of objects, such as Radio Galaxies, Pulsars and Masers. The discovery of the Cosmic Microwave Background Radiation was a particularly significant event. Radio astronomy is conducted using large radio antenna referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The latter has allowed radio sources to be imaged with unprecedented angular resolution.

Taken from Wikipedia

Vacuum

in theory, a space in which there is no matter. However, a perfect vacuum is unobtainable and the term describes a gas at a very low pressure.

Taken from Dictionary of Science

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In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". Even putting aside the complexities of the quantum vacuum, the classical notion of a perfect vacuum with gaseous pressure of exactly zero is only a philosophical concept and never is observed in practice. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they simply call "vacuum" or "free space", and use the term partial vacuum to refer to real vacuum. The Latin term in vacuo is also used to describe an object as being in what would otherwise be a vacuum.

The quality of a vacuum refers to how closely it approaches a perfect vacuum. Residual gas pressure is a primary indicator of quality, and is most commonly measured in units called torr, even in metric contexts. Lower pressures indicate higher quality, although other variables must also be taken into account. See ultra-high vacuum. Quantum theory sets limits for the best possible quality of vacuum, predicting that no volume of space can be perfectly empty. See QCD vacuum, for example. Outer space and interstellar space are naturally occurring high quality vacuums, mostly of much higher quality than can be created artificially with current technology. Low quality artificial vacuums have been used for suction for many years.

Vacuum has been a frequent topic of philosophical debate since Ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury and then inverting the container into a bowl to contain the mercury.

Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.

Taken from Wikipedia

Dalton's Law of Partial Pressures

in a mixture of gases, the total pressure is the sum of the partial pressures of all the gases present. The partial pressure is the pressure a gas in a mixture would exert if it alone occupied the space of volume

Taken from Dictionary of Science

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Dalton's Law of Partial Pressure:

The pressure of a mixture of gases is equal to the sum of the pressures of all of the constituent gases alone.

Mathematically, this can be represented as:

Pressure_Total = Pressure₁ + Pressure₂ ... Pressure_n

Explanation and Discussion:

Dalton's Law explains that the total pressure is equal to the sum of all of the pressures of the parts. This only is absolutely true for ideal gases, but the error is small for real gases. This may at first seem a trivial law, but it can be very valuable in the chemistry lab.

Let's say you want to collect hydrogen gas. To do this, you set up a system that uses a pneumatic trough, a test tube that has a pipetted stopped, a cable that connects the pipett into the pneumatic trough, and a test tube above the cable that collects the hydrogen. Warning: Do not conduct this experiment unless you are under the direction of a chemist or your chemistry teacher. It is dangerous and involves a Bunsen burner and dangerous materials. You submerge the test tube that will collect the hydrogen, and tilt it up so it only contains water. By placing zinc and acid in the pipetted test tube and heating it, hydrogen gas is given off. This gas pumps through the water and enters into the collection test tube. After the first few seconds, the gas will be pure hydrogen. Image of start of hydrogen generation. When the water level is equal in the test tube and the trough, turn off the generator. The pressure inside the test tube will be equal to the atmospheric pressure. Image of pressure equalibrium in hydrogen generator. Now you can use the ideal gas law to determine the number of hydrogen moles in the test tube, right? Not quite.

You see, the water you collected the hydrogen over has vapor pressure that will distort the equation if not accounted for. Because of the Dalton's Law of partial pressure, you know that the pressure in the test tube is from both the hydrogen and the water. To find just the hydrogen, you would have to subtract the vapor pressure of the water. Vapor pressure of water is published in most chemistry books as a table in the appendix, and varies by the temperature of the water.

Calculations with Dalton's Law:

Let's try that last experiment with real numbers. In our lab, the atmospheric pressure is 102.4 kPa. The temperature of our water is 25°C. We used a 250 mL beaker instead of a test tube to collect the hydrogen. Let's find the pressure of the hydrogen, and then find the moles of hydrogen using the ideal gas law.

Step 1: We need to know the vapor pressure of the water. A common table lists the pressure at 25°C as 23.76 torr. A torr is 1 mm of mercury at standard temperature. In kilopascals, that would be 3.17 (1 mm mercury = 7.5 kPa). We should also convert the 250 mL to .250 L and 25°C to 298 L.

Step 2: We can use Dalton's Law to find the hydrogen pressure. It would be:

P_Total = P_Water + P_Hydrogen
102.4 kPa = 3.17 kPa + P_Hydrogen

So the pressure of Hydrogen would be: 99.23 kPa or 99.2 kPa.

Step 3: We use the Ideal Gas Law to get the moles. Recall that the Ideal Gas Law is:

PV=nRT

where P is pressure, V is volume, n is moles, R is the Ideal Gas Constant (0.0821 L-atm/mol-K or 8.31 L-kPa/mol-K), and T is temperature.

Therefore, our equation would be:

99.2 kPa x .250 L = n x 8.31 L-kPa/mol-K x 298 K

This can be re-arranged so:

n = 99.2 kPa x .250 L / 8.31 L-kPa/mol-K / 298 K
n = .0100 mol or 1.00 x 10^-2 mol Hydrogen

Taken from Thinkquest

The Foul-Weather Friend

By Jim Roberts

Sometimes being a friend can be frustrating. What does it take to weather the storms in a relationship?

Jonathan sprang from his place like a cat! The spear swished through the space where he'd been standing, piercing the wall with a sickening thud.

Horrified, Jonathan watched the spear until it stopped vibrating. Then he stared at Saul in disbelief.

Saul, his own father whom he loved and respected, had hurled that spear! Jonathan turned and left quickly. He now realized the danger of being David's friend.

Until recently, it had been easy being friends with David. After he defeated the giant Goliath, David led King Saul's army in repeated military victories. Not only that, but he was the king's personal musician, and the king's son-in-law. David was a national hero.

How quickly all that changed. Because of David's heroics, he became more admired and popular than King Saul. This created a big problem for Saul's ego. His jealousy and envy quickly grew into fear and ultimately hatred.

Saul convinced himself that to gain back his prestige and popularity, he must get rid of David. First he tried to arrange David's death by circumstance. Next, he made personal attempts on David's life.

When these efforts failed, Saul sought the help of his servants and captains. At last, he told his son Jonathan of his intent.

"Find him and kill him!" Saul ordered. David became public enemy No. 1.

Caught in the middle

Jonathan had a lot of thinking to do. Storm clouds had gathered over his friendship with David. How would he handle the foul weather?

David has been his best friend for some time. They were closer than brothers. They had a lot in common. Jonathan, too, was a heroic and valiant warrior. He had similar courage, and faith in God (I Samuel 14:6). Once he attacked and routed an entire enemy camp with only the help of his personal assistant.

Jonathan had been impressed with David ever since he'd seen David defeat Goliath with only a sling and a stone. His admiration and affection for David grew so much that he gave him his own weapons, and the royal garments off his back. This action by a prince was among the highest honors awarded.

The love and respect was mutual. The two had made a special agreement not to let anything come between their friendship. But now this! Jonathan's own father hated David. He even told Jonathan to bring David in so he could be killed! How could Jonathan be loyal to both his father and his friend?

There was an even bigger issue in Jonathan's mind. The prophet Samuel had said that God had chosen David to be the next king over Israel. This meant that Jonathan, although he was the son of the king and was being groomed for the throne, was odd man out.

Jonathan had every human reason to cooperate with his father's murderous scheme. David's death would lock up the throne for him. The friendship was no longer serving his personal interests, so why fight his father's plan?

There was foul weather, all right. There was also intense peer pressure from many who tried to sell Jonathan on his father's plan. What was Jonathan to do?

By befriending David, he received ridicule, shame and accusations of treason. And now the personal attack from his father.

Jonathan thought it through. He knew David was innocent. He'd behaved himself loyally and wisely at all times. He'd broken the stranglehold of the enemy Philistines, and restored Israel to a position of dignity. David hadn't tried to grasp the throne from Saul and was loyal to him.

Besides, Jonathan loved David as his own life. Yet he loved his father also. He knew Saul was rebelling against God. But he wasn't going to rebel against Saul.

Still, Jonathan could not support this unjust treachery against David. That would dishonor God. It was a real dilemma.

Loyal to both

Jonathan had faith in God. He must have spent time talking to God about all this. He finally came to a decision. Jonathan would not forsake his friend. He would loyally serve his father except in the scheme against David.

While Jonathan wrestled with his predicament, David's continued. Things went from bad to desperate. Saul began to ignore otter affairs of kingship for an almost daily pursuit of David. It was increasingly dangerous to have contact with this fugitive.

Yet, when Jonathan heard where his friend was hiding, he took the risk of meeting David. It was to be their last meeting.

David was feeling particularly down in the dumps at this time. Just when he needed him the most, his friend showed up. What a welcome sight!

Jonathan comforted David and renewed their special agreement. He gave needed encouragement, assuring David there was no way Saul would succeed in his plot. He told David he knew God had reserved the throne for him, and pledged his support.

Jonathan and David were closer than brothers. They shared everything, good or bad.

In this last encounter, Jonathan claimed no personal aspirations for the throne. His commitment to the friendship was more important than being king.

Jonathan didn't use this friendship only for what he could get out of it (Proverbs 19:6). Instead, he willingly endangered his own life for David's future (John 15:13). Even in the face of great personal loss, Jonathan gave the support and encouragement needed by his friend.

The story of Jonathan is both happy and tragic. You can read it in I Samuel 17 through II Samuel 2.

As David's death remained Saul's top priority, the Philistines again became aggressive and Israel had to go to battle. Israel was badly beaten in battle and Saul was killed. Tragically, Jonathan and two of his brothers were also slain. Jonathan died loyal to both his father and his friend.

Even with Saul dead, David held no victory party. Instead, he fasted and mourned.

He wrote a sad song then. It's a lament about the tragic death of Saul, and an ode of honor to his friend. In the song, David wrote: "I am distressed for you, my brother Jonathan; you have been very pleasant to me: your love to me was wonderful" (II Samuel 1:26, New King James Version).

Without friends, none of us is likely to become much of anything. Jonathan and David teach the value of friendship.

Good friends are worth more than material possessions or position. David and Jonathan each demonstrated the key to true friendship: selflessness. In a word, love.

Many "friendships" are based on what each party can get out of the relationship. True relationships are based on what each can give to the other.

Jonathan didn't worry about getting the kingdom. The choice he made was selfless: his friend's welfare above his own.

Sure, it was tough being David's friend. But Jonathan stuck with it no matter how tough it got. He was no fair-weather friend (Proverbs 17:17).

By being like Jonathan, we can become something rare and special--a true friend, even in foul weather.

Taken from Youth 90 magazine