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I am sorry. I ran out of time so here are the three "items" that I will post on tonight.

Lyman Alpha Forest,

There is one spectral line that stands out above all others: the transition between the ground state of hydrogen and its first excited state. This is called the Lyman Alpha line.

This energy difference corresponds to a photon with a wavelength of 1216 angstroms.

Because the clouds lie at different distances, they are travelling at different relative velocities, because of the expansion of the universe. This means that their Lyman Alpha lines, as we see them, lie at different places in the spectrum, because of the Doppler effect. This means that there will be many more Lyman Alpha absorption lines--and at larger redshifts--for a distant object than for a nearby object.

For example, this also allows us to plot the positions of the intervening neutral hydrogen between a quasar and us.

Gravitational Lensing

How light is affected by massive gravitational objects in the universe.

Supernova 1987a

Shows that the universe is at least 170,000 years old.

As a background, I thought I would repost some background information prior to my next post tonight:

1. THE STANDARD MODEL:

The best description of how matter and energy interact (sans gravity) is called “The Standard Model” It describes the organization of all of the particles and how they interact. The elementary particles are divided into two families called quarks and leptons. Each family consists of six particles and three of each of the particles in each group are acted on by a force carrier.

Quarks: Six called, up charm, top, down, strange, and bottom. All six quarks are acted upon by gluons and photons. This is because all of them carry electromagnetic charge (u,c,t have a charge of +2/3 e, while d,s,b have a charge of -1/3 e), and all of them carry a color charge. There are three kinds of color charge, which are commonly written as red, green and blue. Every quark in the universe has one of these charges. Each flavor of quark can have any color charge.

Note: Because there is one kind of EM charge, there is one photon, but since there are three kinds of color charge, there are eight gluons. Gluons themselves carry both a color charge and an anti-color charge, so you'd think that there would be nine gluons, but the combination red-antired + blue-antiblue + green-antigreen is colorless, so if you define a red-antired gluon and a blue-antiblue gluon, a green-antigreen gluon can be described as a superposition of the other two. Only eight gluons are needed to span the color space.

Leptons: Six called: e neutrino, u neutrino, t neutrino, electron, muon, and tau. All quarks and leptons couple to both W and Z bosons. A W, for example, transforms an electron to an electron neutrino, or a t-quark to a b-quark.

Gravity is not included in the standard model, however it is believed that is exchange force is a graviton.

THE FOUR FUNDEMENTAL FORCES OF NATURE:

Strong force
Weak force
Electromagnetism (EM)
Gravity

All of the fundamental forces are considered Exchange Forces. In other words the force involves an exchange of one or more particles.

The exchange particles are as follows:

Strong – The pion (and others)

Note: The pion does mediate the inter-nucleon force. That force isn't fundamental, however. The fundamental force is the inter-quark force that binds the quarks into hadrons (such as protons, neutrons and pions), and that is what we usually mean by the strong force, nowadays. The force between hadrons is a residual color dipole interaction that is analogous to the Van der Waals force in electromagnetism.

Lets explore this a bit further:

First, lets take a look at Van der Waals Forces:

Atom and molecules are attracted to each other by two classes of bonds. The Intramolecular bond and the Intermolecular bond.

The Intermolecular bond is divided into these categories; Van der Waals Forces, Hydrogen Bonds, and molecule-ion attractions.

The Intramolecular bond (which are much stronger than the Intermolecular bond) is divided into these categories; Ionic bonding, covalent bonding, and metallic bonds.

We will only concentrate on the Van der Waals Forces.

Van der Waals Forces arise from the interaction of the electrons and nuclei of electrically neutral atoms and molecules. How is this possible if these are considered electrically neutral I hear you ask. What is going on here is that the electrons and nuclei of atoms and molecules (for this description: from here out called particles) are not at rest, but are in a constant motion. Since this is the case, there arises an electrical imbalance (called an instantaneous dipole [another term is a temporary polarity]) in this electrically neutral particle. Two “particles” in this dipole state will attract. Also this dipole action in one particle can cause a dipole in an adjoining (nearby) particle. So the dipole-dipole attraction is what is known as Van der Waals Forces. If these “particles” kinetic energies are low enough (anc close enough together), the repeated actions of the instantaneous dipoles will keep them attracted together.

One of the interesting things about this that the more electrons are in play the greater the Van der Waals Force. This is why the noble gas Krypton liquefies at a higher temperature than the noble gas Neon.

Back to the Standard Model.

A brief background: How does a nucleus stay together when it is packed with positively charged protons? Since “like” charges repel, you would think that the nucleus would fly apart. The force that keeps this from happening is the Strong Force. One of the things that was discovered is that the mass of any nucleus is always less than the sum of the individual particles (called nucleons) that make it up. The difference (residual) is due to the “Binding Energy” of the nucleus. This binding energy is directly related to the strength of the strong force. "Binding energy" is a negative energy. This binding enery folows a curve called the Nuclear Binding Energy Curve. The lighter elements from Hydrogen up to Sodium exibit an increase in the binding energy and there is a stable area from Magnesium thru Xenon. Iron is the most tightly bound element.

However, for nuclei above iron, the binding energy becomes less and less; the strong nuclear force creates stable minima in which very heavy nuclei can exist, but these are but local minima sitting high on the electromagnetic hill. A uranium nucleus is heavier than thorium plus helium.

So just what is this Strong Force anyway? The Strong force has an effect on quarks, anti quarks and gluons. Oh my, another term, QUARKS! After much research, it was discovered that the protons and neutrons in the nucleus were made up of smaller particles called quarks. It turned out that two types of quarks were needed to “produce” a proton or a neutron. However, there are six types of quarks in normal matter. The strong force binds these quarks together to form a family of particles called hadrons which include both protons and neutrons.

To simplify this discussion, quarks have a “color charge” (red, green, and blue). BTW, this was a convenient way of describing the charge, it is not referring to color as we commonly use it). Like colors repel and unlike colors attract. There are also antiquarks. If it is a quark/antiquark (same color) it is called a meson. If it’s between quarks it is called a baryon (protons and neutrons fall in this category). Here is the rub, baryonic particles can exist if their total color is neutral (colorless); i.e. have a red green and blue charge altogether. Both mesons and baryons are "colorless" with respect to the outside world. In baryons red + blue + green = colorless. In mesons, for example, red + anti-red (or, if you like, red - red) = colorless.

Without getting into too much more detail, quarks can interact, changing color, etc. so long as the total charge is conserved.

The quark interactions are cause by exchanging particles called gluons. There are eight kinds of gluons each having a specific “color” charge. The symmetry group of Quantum Chromodynamics is SU(3). In the minimal representation of SU(3), there are three generators...the color charges. In the non-minimal representation, there are 3²-1 generators...the eight gluons! This was spookily mirrored by Murray Gell-Mann's original (1964) quark theory, which also exploited the SU(3) symmetry. Only this time, the minimal representation was the three light quark flavors (up, down, strange), and the non-minimal representation was Gell-Mann's famous Eightfold Way, which correctly(!) predicted the properties of all the light hadrons, including some that had not yet been discovered.

So back to the original paragraph: Neutral (all three colors) hadrons (which include protons and neutrons) can interact with the strong force similarly to the way atoms an molecules react via the Van der Waals forces.

Electromagnetic (EM) – The photon
Weak – The W and Z
Gravity – The graviton

So to sum this up:

The Strong Force:
It is a force that holds the nucleus together against the repulsion of the Protons. It is not an inverse square force like EM and has a very short range. It is the strongest of the fundamental forces.

The Weak Force:
The weak force is the force that induces beta decay via interaction with neutrinos. A star uses the weak force to “burn” (nuclear fusion). Three processes we observe are proton-to proton fusion, helium fusion, and the carbon cycle. Here is an example of proton-to-proton fusion, which is the process our own sun uses: (two protons fuse -> via neutrino interaction one of the protons transmutes to a neutron to form deuterium -> combines with another proton to form a helium nuclei -> two helium nuclei fuse releasing alpha particles and two protons). The weak force is also necessary for the formation of the elements above iron. Due to the curve of binding energy (iron has the most tightly bound nucleus), nuclear forces within a star cannot form any element above iron in the periodic table. So it is believed that all higher elements were formed in the vast energies of supernovae. In this explosion large fluxes of energetic neutrons are produced which produce the heavier elements by nuclei bombardment. This process could not take place without neutrino involvement and the weak force.

Electromagnetism:
The electromagnetic force is the forces between charges (Coulomb’ Law) and the magnetic force which both are describe within the Lorentz Force Law. Electric and magnetic forces are manifestations of the exchange of photons. A photon is a quantum particle of light (electromagnetic radiation). This particle has a zero rest mass The relativistic mass of a photon is also zero. Gravity couples to energy density, which is typically dominated by mass. But even in Newtonian gravity, massless light particles will bend in a gravitational field (the trajectory of a test particle doesn't depend on mass). The speed of light in a vacuum is a constant and is unobtainable by baryonic matter due to the lorentz transformation. Electromagnetism obeys the “inverse square law”.

Gravity:
Gravity is the weakest of the forces and also obeys the inverse square law. The force is only attractive and is a force between any two masses. Gravity is what holds and forms the large scale structures of the universe such as galaxies.

I added this as further background for your reading enjoyment: :-)

Noise Temperature

Astronomers use temperature to represent the strength of detected radiation. Any body with a temperature above -273 deg C (approximately absolute 0) emits electromagnetic radiation (EM). This thermal radiation isn't just in the infrared but is exhibited across the entire electromagnetic spectrum. (Note: it will have a greater intensity (peak) at a specific area of the EM spectrum depending on its temperature). For example, bodies at 2000 K (Kelvin), the radiation is primarily in the infrared region and at 10000 K, the radiation is primarily in the visible light region. There is also a direct correlation between temperature and the amount of energy emitted, which is described by Planck's law.

When the temperature of a body decreases, two things happen. First, the peak shifts in the direction towards the longer wavelengths and second, it emits less radiation at all wavelengths.

This turns out to be extremely useful. When a radio astronomer looks at a particular location of the sky and exclaims that it has a noise temperature of 1500 K, he/she isn't declaring how hot the body (nebulae, etc) really is, but is providing a measurement of the strength of the radiation from the source at the observed frequency. For example, radiation from an extra solar body may be heated from a nearby source such as a star. If this body is radiating at a temperature of 500 K, it exhibits the same emissions across all frequencies that a local test source does. The calculated noise figure will be the same across all frequencies. (Note: this does not take into account other sources of radiation such as synchrotron radiation).

A problem for radio astronomers is that not only the observed source emits thermal radiation; the local environment (ground, atmosphere, etc) and the equipment (antenna, amplifiers, cables, receiver, etc) being used to make the measurements also emit thermal radiation. To accurately observe and measure the distant sources, the radio astronomer must subtract all of the local environment and detection equipment noise additions.

Back in 1963, Arno Penzias and Robert Wilson were working with a horn antenna trying to obtain the high efficiency possible for the Telstar project. This antenna was also going to be used for radio astronomy at a later date. They pointed it to a quiet part of the sky and took measurements. When they subtracted all of the known sources of noise, they found approximately 3 K left over. They worked very diligently to eliminate/describe this noise source and were unable to. This mysterious source of noise seemed to be there no matter where they pointed the antenna. What they had discovered was the microwave background produced from the Big Bang. This 3 (closer to 2.7) K microwave background originated approximately 300,000 years after the Big Bang itself had occurred. It has been determined that when these signals originated, the universe had already cooled down to around 3000 K.

The Interstellar Medium

Between the stars and galaxies is mostly empty space. However, this space is not entirely empty. It is filled with a diffuse medium of gas and dust called the Interstellar Medium (ISM). The ISM primarily consists of neutral hydrogen gas (HI), molecular gas (mostly H2, ionized gas (HII), and dust grains. Even though this considered a very good vacuum, the ISM in our galaxy comprises about five percent of the mass of the visible part (stars etc) of our galaxy.

Neutral Hydrogen Gas:

Our own galaxy is filled with a diffuse distribution of neutral hydrogen gas. This gas has a density of approximately one atom per centimeter cubed. One of the features of the neutral hydrogen is the radio wave production at 21 centimeters due to the spin properties of the atom. This neutral hydrogen is distributed in a clumpy fashion with cooler denser regions called “clouds”.

Molecular Clouds:

Denser than the surrounding regions, clouds of molecular hydrogen and dust are the birthplace of stars. We are unable to detect molecular hydrogen directly, however we can infer its characteristics from other molecules present (usually CO). There have been over 50 different molecules detected in these clouds including NH3, CH, OH, CS, etc. Some molecular clouds can be as large as 150 light years in diameter. There are thousands of these clouds in our galaxy, usually situated in the spiral arms and concentrated towards the center of the galaxy.

Ionized Hydrogen Regions:

The ionized hydrogen (HII) is the remnants left from the formation of the younger hotter stars. These produce the more visible nebula such as the Orion Nebula. O and B class stars recently formed in molecular clouds ionize the gas left over from their formation. This results in the gas being heated to a temperature of about 10,000K causing it to fluoresce producing emission line spectrums. Hydrogen atoms absorb photons and are ionized from the “extra” energy. This and other features such as collisions produce the emission features of both the hydrogen and helium in the visible nebula.

Interstellar Dust:

Around one percent of the ISM is in the form of tiny grains of dust. These grains are approximately the size of a particle of cigarette smoke. This dust blocks the plane of our Milky Way galaxy form our view. We can determine the composition of these dust clouds by the way if affects different frequencies of photons. One of the affects of these dust clouds is that they dim the light from distant objects. This dimming is called interstellar extinction. It also reddens the color (interstellar reddening) due to the fact that red light is not scattered as efficiently as blue light is. The characteristics for the dust particles vary throughout the galaxy. However, a typical grain of dust is composed of carbon mixed with silicates. Almost all of the elements such as carbon and silicon found in the ISM are found in the dust particles.