CBR - Cosmic Background Radiation

CMB stands for Cosmic Microwave Background. It is also sometimes called the CBR, for Cosmic Background Radiation, although this is really a more general term that includes other cosmological backgrounds, eg infra-red, radio, x-ray, gravity-wave, neutrino. The CMB contains hugely more energy than any other cosmic radiation source, however, so it is the dominant component of the overall CBR spectrum. Other acronyms, such as CMBR, are also sometimes used!

Background radiation is the ionizing radiation emitted from a variety of natural and artificial radiation sources. Primary contributions come from,

* Sources in the Earth. These include sources in our food and water, which are incorporated in our body, and in building materials and other products that incorporate those radioactive sources;
* Sources from space, in the form of cosmic rays;
* Sources in the atmosphere. One significant contribution comes from the radon gas is released from the earth's crust and subsequently decays to radioactive atoms that become attached to airborne dust and particulates. Another contribution arises from the radioactive atoms produced in the bombardment of atoms in the upper atmosphere by high-energy cosmic rays.

Today, a small fraction of background radiation also comes from radioactive tools such as smoke detectors, from self-luminous dials and signs, from global radioactive contamination due to historical nuclear weapons testing, nuclear power station or nuclear fuel reprocessing accidents, and from normal operation of the nuclear power industry. Sometimes included in background radiation are routine medical procedures like X-ray imaging; this is purposeful diagnostic exposure which dwarfs all other human-caused background radiation in the population of the industrialized world.

The Big Bang theory predicts that the early universe was a very hot place and that as it expands, the gas within it cools. Thus the universe should be filled with radiation that is literally the remnant heat left over from the Big Bang, called the “cosmic microwave background radiation”, or CMB.

The existence of the CMB radiation was first predicted by George Gamow in 1948, and by Ralph Alpher and Robert Herman in 1950. It was first observed inadvertently in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New Jersey. The radiation was acting as a source of excess noise in a radio receiver they were building. Coincidentally, researchers at nearby Princeton University, led by Robert Dicke and including Dave Wilkinson of the WMAP science team, were devising an experiment to find the CMB. When they heard about the Bell Labs result they immediately realized that the CMB had been found. The result was a pair of papers in the Physical Review: one by Penzias and Wilson detailing the observations, and one by Dicke, Peebles, Roll, and Wilkinson giving the cosmological interpretation. Penzias and Wilson shared the 1978 Nobel prize in physics for their discovery. Today, the CMB radiation is very cold, only 2.725° above absolute zero, thus this radiation shines primarily in the microwave portion of the electromagnetic spectrum, and is invisible to the naked eye. However, it fills the universe and can be detected everywhere we look. In fact, if we could see microwaves, the entire sky would glow with a brightness that was astonishingly uniform in every direction. The picture at left shows a false color depiction of the temperature (brightness) of the CMB over the full sky (projected onto an oval, similar to a map of the Earth). The temperature is uniform to better than one part in a thousand! This uniformity is one compelling reason to interpret the radiation as remnant heat from the Big Bang; it would be very difficult to imagine a local source of radiation that was this uniform. In fact, many scientists have tried to devise alternative explanations for the source of this radiation but none have succeeded.

In below image, red denotes hotter fluctuations and blue and black denote cooler fluctuations around the average. These fluctuations are extremely small, representing deviations from the average of only about 1/100,000 of the average temperature of the observed background radiation.



Why study the Cosmic Microwave Background?

Since light travels at a finite speed, astronomers observing distant objects are looking into the past. Most of the stars that are visible to the naked eye in the night sky are 10 to 100 light years away. Thus, we see them as they were 10 to 100 years ago. We observe Andromeda, the nearest big galaxy, as it was about 2.5 million years ago. Astronomers observing distant galaxies with the Hubble Space Telescope can see them as they were only a few billion years after the Big Bang. (Most cosmologists believe that the universe is between 12 and 14 billion years old.)

The CMB radiation was emitted only a few hundred thousand years after the Big Bang, long before stars or galaxies ever existed. Thus, by studying the detailed physical properties of the radiation, we can learn about conditions in the universe on very large scales, since the radiation we see today has traveled over such a large distance, and at very early times.

The Origin of the Cosmic Microwave Background

One of the profound observations of the 20th century is that the universe is expanding. This expansion implies the universe was smaller, denser and hotter in the distant past. When the visible universe was half its present size, the density of matter was eight times higher and the cosmic microwave background was twice as hot. When the visible universe was one hundredth of its present size, the cosmic microwave background was a hundred times hotter (273 degrees above absolute zero or 32 degrees Fahrenheit, the temperature at which water freezes to form ice on the Earth's surface). In addition to this cosmic microwave background radiation, the early universe was filled with hot hydrogen gas with a density of about 1000 atoms per cubic centimeter. When the visible universe was only one hundred millionth its present size, its temperature was 273 million degrees above absolute zero and the density of matter was comparable to the density of air at the Earth's surface. At these high temperatures, the hydrogen was completely ionized into free protons and electrons. Since the universe was so very hot through most of its early history, there were no atoms in the early universe, only free electrons and nuclei. (Nuclei are made of neutrons and protons). The cosmic microwave background photons easily scatter off of electrons. Thus, photons wandered through the early universe, just as optical light wanders through a dense fog. This process of multiple scattering produces what is called a “thermal” or “blackbody” spectrum of photons. According to the Big Bang theory, the frequency spectrum of the CMB should have this blackbody form. This was indeed measured with tremendous accuracy by the FIRAS experiment on NASA's COBE satellite.


This figure shows the prediction of the Big Bang theory for the energy spectrum of the cosmic microwave background radiation compared to the observed energy spectrum. The FIRAS experiment measured the spectrum at 34 equally spaced points along the blackbody curve. The error bars on the data points are so small that they can not be seen under the predicted curve in the figure! There is no alternative theory yet proposed that predicts this energy spectrum. The accurate measurement of its shape was another important test of the Big Bang

“Wall of Light - Surface of Last Scattering”

Eventually, the universe cooled sufficiently that protons and electrons could combine to form neutral hydrogen. This was thought to occur roughly 400,000 years after the Big Bang when the universe was about one eleven hundredth its present size. Cosmic microwave background photons interact very weakly with neutral hydrogen.

he behavior of CMB photons moving through the early universe is analogous to the propagation of optical light through the Earth's atmosphere. Water droplets in a cloud are very effective at scattering light, while optical light moves freely through clear air. Thus, on a cloudy day, we can look through the air out towards the clouds, but can not see through the opaque clouds. Cosmologists studying the cosmic microwave background radiation can look through much of the universe back to when it was opaque: a view back to 400,000 years after the Big Bang. This “wall of light“ is called the surface of last scattering since it was the last time most of the CMB photons directly scattered off of matter. When we make maps of the temperature of the CMB, we are mapping this surface of last scattering.

As shown above, one of the most striking features about the cosmic microwave background is its uniformity. Only with very sensitive instruments, such as COBE and WMAP, can cosmologists detect fluctuations in the cosmic microwave background temperature. By studying these fluctuations, cosmologists can learn about the origin of galaxies and large scale structures of galaxies and they can measure the basic parameters of the Big Bang theory.

Problems with the Uniformity
The highly isotropic nature of the cosmic background radiation indicates that the early stages of the Universe were almost completely uniform. This raises two problems for the big bang theory.

First, when we look at the microwave background coming from widely separated parts of the sky it can be shown that these regions are too separated to have been able to communicate with each other even with signals travelling at light velocity. Thus, how did they know to have almost exactly the same temperature? This general problem is called the horizon problem.

Second, the present Universe is homogenous and isotropic, but only on very large scales. For scales the size of superclusters and smaller the luminous matter in the universe is quite lumpy, as illustrated in the following figure.


Data from the survey of galaxies. The voids and "walls" that form the large-scale structure are mapped here by 11,000 galaxies. Our galaxy, the Milky Way, is at the center. The outer radius is at a distance of approximately 450 million light-years. Obscuration by the plane of the Milky Way is responsible for the missing pie-shaped sectors to the right and left. Click on the image to get a larger version. (Smithsonian Astrophysical Observatory, 1993. Northern data (top)--Margaret Geller and John Huchra, Southern data (bottom)--Luiz da Costa et al. Quoted in Cosmology, a Research Briefing, National Academy of Sciences

What's "Cosmic" about it?

We refer to it as "cosmic" because the only known source of this radiation is the early universe. It can now be firmly concluded that the CMB is the cooled remnant of the hot Big Bang itself.

Why "Microwave"?

Light comes in a range of wavelengths, from the shortest wavelength gamma-rays to the longest wavelength radio waves, with common-or-garden visible light in the middle. All of these signals are manifestations of the same underlying physical phenomenon, travelling packets of oscillating electric and magnetic fields, called electro-magnetic radiation. All of the forms of electromagnetic radiation travel at the same speed, the speed of light, which is 300,000 km/s. E-m radiation of different wavelengths will interact with matter in different ways. For example, radio waves are picked up by a radio receiver, your eye detects visible light, infra-red radiation warms your skin, x-rays penetrate your body, gamma-rays can give you radiation damage.

Microwaves are the name given to radiation between the infra-red and radio region, with wavelengths typically in the 1mm to 10cm range. Some specific wavelengths of microwaves can be used to excite the molecules in foodstuff, so that you can use them to cook. It turns out that if you had a sensitive microwave telescope in your house you would detect a faint signal leaking out of your microwave oven, and from various other man-made sources, but also a faint signal coming from all directions that you pointed. This is the Cosmic Microwave Background.

Why is it called a "Background"?

We refer to this radiation as a background because we see it no matter where we look. It clearly doesn't come from any nearby objects, such as stars or clouds within our Galaxy, or even from external galaxies. It is clearly a distant, "background" source of radiation. You can think of the whole Universe as being filled with this background of microwave photons.
How do I pronounce "anisotropy"?

If you've never come across this word before, then (obviously) it's new to you, and so even professional cosmologists sometimes pronounce it wrongly. This then is a good question, but hard to answer in plain text! Basically, the stress is on the third syllable, and the common mistake is to stress the fourth. The confusion presumably arises from knowing how to pronounce "anisotropic", and then thinking that you just pronounce it the same way, but without the final consonant.

Why does the CMB support the Big Bang picture?

The basic point is that the spectrum of the CMB is remarkably close to the theoretical spectrum of what is known as a "blackbody", which means an object in "thermal equilibrium". Thermal equilibrium means that the object has had long enough to settle down to its natural state. Your average piece of hot, glowing coal, for example, is not in very good thermal equlibrium, and a "blackbody" spectrum is only a crude approximation for the spectrum of glowing embers. But it turns out that the early Universe was in very good thermal equilibrium (basically because the timescale for settling down was very much shorter than the expansion timescale for the Universe). And hence radiation from those very early times should have a spectrum very close to that of a blackbody.

The observed CMB spectrum is in fact better than the best blackbody spectrum we can make in a laboratory! So it is very hard to imagine that the CMB comes from emission from any normal "stuff" (since if you try to make "stuff" at some temperature, it will tend to either emit or absorb preferentially at particular wavelengths). The only plausible explanation for having this uniform radiation, with such a precise blackbody spectrum, is for it to come from the whole Universe at a time when it was much hotter and denser than it is now. Hence the CMB spectrum is essentially incontrovertible evidence that the Universe experienced a "hot Big Bang" stage (that's not to say that we understand the initial instant, just that we know the Universe used to be very hot and dense and has been expanding ever since).

In full, the three cornerstones of the Big Bang model are: (1) the blackbody nature of the CMB spectrum; (2) redshifting of distant galaxies (indicating approximately uniform expansion); and (3) the observed abundances of light elements (in particular helium and heavy hydrogen), indicating that they were "cooked" throughout the Universe at early times. Because of these three basic facts, all of which have strengthened over the decades since they were discovered, and several supporting pieces of evidence found in the last deacade or two, the Big Bang model has become the standard picture for the evolution of our Universe.

Can I see the CMB for myself?

In fact you can! If you tune your TV set between channels, a few percent of the "snow" that you see on your screen is noise caused by the background of microwaves.

How come we can tell what motion we have with respect to the CMB?

Doesn't this mean there's an absolute frame of reference?

The theory of special relativity is based on the principle that there are no preferred reference frames. In other words, the whole of Einstein's theory rests on the assumption that physics works the same irrespective of what speed and direction you have. So the fact that there is a frame of reference in which there is no motion through the CMB would appear to violate special relativity!

However, the crucial assumption of Einstein's theory is not that there are no special frames, but that there are no special frames where the laws of physics are different. There clearly is a frame where the CMB is at rest, and so this is, in some sense, the rest frame of the Universe. But for doing any physics experiment, any other frame is as good as this one. So the only difference is that in the CMB rest frame you measure no velocity with respect to the CMB photons, but that does not imply any fundamental difference in the laws of physics.

The indication of the above image is that the local group of galaxies, to which the Earth belongs, is moving at about 600 km/s with respect to the background radiation. It is not know why the Earth is moving with such a high velocity relative to the background radiation.

What sort of telescope is used to observe the CMB?

Like light at any other wavelength the general system is a dish to collect and focus the radiation, a way of feeding the radiation to the instruments, and then the instruments themselves which are used to detect and record the signals. For microwaves the dish, or set of dishes, is made of a material (metal) which reflects microwaves. The focussed radiation is transported to the receivers by means of "wave-guides", which are pipes specially tuned to transmit microwave signals.

Resources:
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html
http://csep10.phys.utk.edu/astr162/lect/cosmology/cbr.html
http://en.wikipedia.org/wiki/Background_radiation
http://www.astro.ubc.ca/people/scott/faq_basic.html

Supernova ... Ka Boom!!!

A supernova (pl. supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months. A supernova briefly outshines its entire host galaxy. It would take 10 billion years for the Sun to produce the energy output of an ordinary Type II supernova. Stars beneath the Chandrasekhar limit[1] , such as the Sun, are too light to ever become supernovae and will evolve into white dwarfs[2]

Types of Supernovae

Supernovae are divided into two basic physical types:

Type Ia.

These result in some Binary-Star[3] systems in which a carbon-oxygen white dwark is accreting matter from a companion. (What kind of companion star is best suited to produce Type Ia supernovae is hotly debated.) In a popular scenario, so much mass piles up on the white dwarf that its core reaches a critical density of 2 x 109 g/cm3. This is enough to result in an uncontrolled fusion of carbon and oxygen, thus detonating the star.

Type II.

These supernovae occur at the end of a massive star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star's iron core is massive enough then it will collapse and become a supernova.

However, these types of supernovae were originally classified based on the existence of hyderogen, Spectral Lines[4]. Type Ia do not show hydrogen lines, while Type II do.

In general this observational classification agrees with the physical classification outlined above, because massive stars have atmospheres (made of mostly hydrogen) while white dwarf stars are bare. However, if the original star was so massive that its strong Stellar Wind[5] had already blown off the hydrogen from its atmosphere by the time of the explosion, then it too will not show hydrogen Spectral Lines. These supernovae are often called Type Ib supernovae, despite really being part of the Type II class of supernovae. Looking at this discrepancy between our modern classification (based on a true difference in how supernovae explode), and the historical classification (based on early observations) shows how classifications in science can change over time as we better understand the natural world.

What Causes a Star to Blow Up?

Gravity gives the supernova its energy. For Type II supernovae, mass flows into the core by the continued making of iron from Nuclear-Fusion[6]. Once the core has gained so much mass that it cannot withstand its own weight, the core implodes (A violent inward collapse-An inward explosion). This implosion can usually be brought to a halt by neutrons, the only things in nature that can stop such a gravitational collapse (when a body falls under its own mass). Even neutrons sometimes fail depending on the mass of the star's core. When the collapse is abruptly stopped by the neutrons, matter bounces off the hard iron core, thus turning the implosion into an explosion: ka-BOOM!!!

For Type Ia supernova, the energy comes from the run-away fusion of carbon and oxygen in the core of the white dwarf.

Where Does the Core Go?

When the core is lighter than about 5 solar masses (A unit of mass equivalent to the mass of the Sun. 1 solar mass = 1 M_sun = 2 x 10³³ grams), it is believed that the neutrons are successful in halting the collapse of the star creating a neutron star. Neutron stars can sometimes be observed as Pulsars[7] or X-Ray binaries.

When the core is heavier (M_core > ~ 5 solar masses), nothing in the known universe is able to stop the core collapse, so the core completely falls into itself, creating a black hole(An object whose gravity is so strong that even light can not escape from it)

To understand the phenomenon of core collapse better, consider an analogy to a rocket escaping the Earth's gravity. According to Newton's law of Gravity, the energy it takes to completely separate two things is given by:

E = G M m / r

where G is the Gravitational constant, M is the mass of the Earth, m is the mass of the rocket and r is the distance between them (the radius of the Earth). When the rocket is shot off at a given velocity v, its energy is:

E = 1/2 m v²

For the rocket to escape the Earth's gravitational field, this energy must be as least as great as the gravitational energy described in the first equation. Thus, to determine if the rocket will completely break free from the Earth's grasp, we set the two equations equal to one another and solve for v:

v = ( 2 G M / r )^1/2

This result is called the escape velocity. For the Earth, the escape velocity is 11 km/sec.

Next imagine a star's central core in the role of the Earth in the above analogy. Consider what would happen if during the core collapse, the central core became so dense (i.e., the radius became very small while its mass stays the same) that something would have to travel faster than light to escape. Whenever this phenomenon occurs (i.e., M_core > ~ 5 solar masses), the supernova creates a black hole from the core of the original star. Now the escape velocity greater than the speed of light -- 300,000 km/sec.

Where Does Most of the Star Go?

The core is only the very small center of an extremely large star that for many millions of years had been making many (but not all) of the elements that we find here on Earth. When a star's core collapses, an enormous blast wave is created with the energy of about 10²⁸ mega-tons (The same amount energy as 1 million tons of TNT - 1 mega-ton = 4 x 10²² ergs = 4 x 10¹⁵ joules).This blast wave plows the star's atmosphere into interstellar space, propelling the elements created in the explosion outward as the star becomes a supernova remnant.

Are We Made of Stardust?

Many of the more common elements were made through nuclear-fusion in the cores of stars, but many were not as well. Because nuclear fusion reactions that make elements heavier than iron require more energy than they give off, such reactions do not occur under stable conditions that occur in stars. Supernovae, on the other hand, are not stable, so they can make these heavy elements beyond iron.

In addition to making elements, supernovae scatter the elements (made by both the star and supernova) out in to the Interstellar-Medium[8]. These are the elements that make up stars, planets and everything on Earth -- including ourselves.

How Often Do Supernovae Occur?

Although many supernovae have been seen in nearby galaxies, supernova explosions are relatively rare events in our own Galaxy, happening once a century or so on average. The last nearby supernova explosion occurred in 1680, It was thought to be just a normal star at the time, but it caused a discrepancy in the observer's star catalogue which historians finally resolved 300 years later, after the supernova remnant (Cassiopeia A) was discovered and its age estimated. Before 1680, the two most recent supernova explosions were observed by the great astronormers Tycho and Kepler in 1572 and 1604 respectively.

In 1987 there was a supernova explosion in the Large Magellanic Cloud, a companion galaxy to the Milky Way. Supernova 1987A, which is shown at the top of the page, is close enough to continuously observe as it changes over time thus greatly expanding astronomers' understanding of this fascinating phenomenon.

(this observation is updated as per 2004 - there may be some more supernovas explosion spotted between 2004-2006)

A picture of Supernova (Supernova 1987A) After & Before explosion is shown below.
The above two photographs are of the same part of the sky. The photo on the left was taken in 1987 during the supernova explosion of SN 1987A, while the right hand photo was taken beforehand. Supernovae are one of the most energetic explosions in nature, making them like a 10²⁸ mega-ton bomb (i.e., a few octillion nuclear warheads).

Definitions:

[1]Chandrasekhar limit: A limit which mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about 1.4 solar masses. Any degenerate object more massive must inevitably collapse into a neutron star

[2]White dwarf: A star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size. Typically, a white dwarf has a radius equal to about 0.01 times that of the Sun, but it has a mass roughly equal to the Sun's. This gives a white dwarf a desnsity about 1 million times that of water!]

[3]Binary star: Binary stars are two stars that orbit around a common center of mass. An X-ray binary is a special case where one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole, and the separation between the stars is small enough so that matter is transferred from the normal star to the compact star star, producing X-rays in the process)

[4]Spectral Line: Light given off at a specific frequency by an atom or molecule. Every different type of atom or molecule gives off light at its own unique set of frequencies; thus, astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of the gas's characteristic frequencies. For example, carbon monoxide (CO) has a spectral line at 115 Gigahertz (or a wavelength of 2.7 mm))

[5]Stellar wind: The ejection of gas off the surface of a star. Many different types of stars, including our Sun, have stellar winds; however, a star's wind is strongest near the end of its life when it has consumed most of its fuel)

[6]Nuclear Fusion: A nuclear process whereby several small nuclei are combined to make a larger one whose mass is slightly smaller than the sum of the small ones. The difference in mass is converted to energy by Einstein's famous equivalence "Energy = Mass times the Speed of Light squared". This is the source of the Sun's energy.

[7]Pulsar: A rotating neutron star which generates regular pulses of radiation. Pulsars were discovered by observations at radio wavelengths but have since been observed at optical, X-ray, and gamma-ray energies.

[8]Interstellar medium: The gas and dust between stars, which fills the plane of the Galaxy much like air fills the world we live in. For centuries, scientists believed that the space between the stars was empty. It wasn't until the eighteenth century, when William Herschel observed nebulous patches of sky through his telescope, that serious consideration was given to the notion that interstellar space was something to study. It was only in the last century that observations of interstellar material suggested that it was not even uniformly distributed through space, but that it had a unique structure.

Resources:
http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html
http://en.wikipedia.org/wiki/Supernova

Some Gyaan on Meteor

What are meteor showers?

Meteor showers are annual events, during which more shooting stars than usual can be seen over a period of several nights, each meteor appearing to point back to (or "radiate from") a particular point in the sky. These meteor showers actually occur because the earth, in its annual orbit around the sun, passes through a particular band of dust particles called a "meteoroid stream". During the course of a full solar year - when the Earth goes one full revolution around the Sun - we encounter many such meteoroid streams large and small!

Meteoroid streams are in fact the debris trails left behind by periodic comets, or in rare cases (e.g., the Geminids) by asteroids. Meteoroid streams can be visualized (in the words of Stuart Atkinson) as "rivers of crumbling comet dust". However, though streams may derive from a comet, there are forces which constantly act on the particles in meteoroid streams to move them around: thus, the meteor shower's "orbit" need not correspond with a parent comet's orbit! And it is in fact this very motion that makes meteoroid streams and their associated showers so interesting...

Where can I see meteor showers?

Meteoroid streams are always much wider than the Earth. Because of this, you will see a shower's meteors scattered over your whole sky, not for just one night but for from 3 up to 60 nights each year! Thus you don't need to face any one direction to see a meteor shower well! Nor will a meteor shower only be visible from one area of the earth. Unlike geographically narrow astronomical events like solar eclipses, lunar occultations, or bright fireballs, a meteor shower will often be visible over much of the Earth's surface!

However, not all of Earth will be able to see a given meteor shower. That is because the bulk of our globe shields some areas of Earth's surface from the impact of meteoroid particles - in effect, some area of the world map is always in the Earth's "shadow" with respect to any meteoroid stream. This "shadow" is bounded by the area of Earth in which a certain point on the Celestial Sphere (the "bowl" of the Heavens) is not visible. This special point is unique to each meteor shower, and is characterized as being the point in the sky to which all visible tracks in the heavens of meteors from the shower - no matter where they are seen in the sky, or from what point on Earth - all seem to trace back to. This point is the "radiant" of a shower!

Finally, because there is of within meteoroid streams, which the earth will "sample" as it passes through them from hour to hour, not all areas of the Earth will necessarily see the exact same show from a meteor shower! For instance, the peak activity for a particular shower may occur while it is daylight in your area of the earth! Or it may be dark during the shower's peak "maximum", but the shower radiant point may be low on your horizon, reducing the number of meteors you see - or again below the horizon, making it impossible to see any meteors from the shower at that particular hour.

Calender for 2007 Shower - http://www.imo.net/calendar/2007
================================================================

Shower	Activity	Max Date	λ	α	δ	v∞	r	ZHR
Antihelion Source (ANT)	Jan 01 - Dec 31					30	3.0	3
Quadrantids (QUA)	Jan 01 - Jan 05	Jan 04	283°16	230°	+49°	41	2.1	120
α-Centaurids (ACE)	Jan 28 - Feb 21	Feb 08	319°2	211°	-59°	56	2.0	5
δ-Leonids (DLE)	Feb 15 - Mar 10	Feb 25	336°	168°	+16°	23	3.0	2
γ-Normids (GNO)	Feb 25 - Mar 22	Mar 14	353°	239°	-50°	56	2.4	4
Lyrids (LYR)	Apr 16 - Apr 25	Apr 22	32°32	271°	+34°	49	2.1	18
π-Puppids (PPU)	Apr 15 - Apr 28	Apr 24	33°5	110°	-45°	18	2.0	var
η-Aquarids (ETA)	Apr 19 - May 28	May 06	45°5	338°	-01°	66	2.4	60
η-Lyrids (ELY)	May 03 - May 12	May 09	48°4	287°	+44	44	3.0	3
June Bootids (JBO)	Jun 22 - Jul 02	Jun 27	95°7	224°	+48°	18	2.2	var
Piscis Austrinids (PAU)	Jul 15 - Aug 10	Jul 28	125°	341°	-30°	35	3.2	5
South.δ-Aquarids (SDA)	Jul 12 - Aug 19	Jul 28	125°	339°	-16°	41	3.2	20
α-Capricornids (CAP)	Jul 03 - Aug 15	Jul 30	127°	307°	-10°	23	2.5	4
Perseids (PER)	Jul 17 - Aug 24	Aug 13	140°0	46°	+58°	59	2.6	100
κ-Cygnids (KCG)	Aug 03 - Aug 25	Aug 18	145°	286°	+59°	25	3.0	3
α-Aurigids (AUR)	Aug 25 - Sep 08	Sep 01	158°6	84°	+42°	66	2.6	7
September Perseids (SPE)	Sep 05 - Sep 17	Sep 09	166°7	60°	+47°	64	2.9	5
δ-Aurigids (DAU)	Sep 18 - Oct 10	Oct 04	191°	88°	+49°	64	2.9	2
Draconids (GIA)	Oct 06 - Oct 10	Oct 09	195°4	262°	+54°	20	2.6	var
ε-Geminids (EGE)	Oct 14 - Oct 27	Oct 18	205°	102°	+27°	70	3.0	2
Orionids (ORI)	Oct 02 - Nov 07	Oct 21	208°	95°	+16°	66	2.5	23
Leo Minorids (LMI)	Oct 19 - Oct 27	Oct 24	211°	162°	+37°	62	3.0	2
Southern Taurids (STA)	Oct 01 - Nov 25	Nov 05	223°	52°	+15°	27	2.3	5
Northern Taurids (NTA)	Oct 01 - Nov 25	Nov 12	230°	58°	+22°	29	2.3	5
Leonids (LEO)	Nov 10 - Nov 23	Nov 18	235°27	153°	+22°	71	2.5	15+
α-Monocerotids (AMO)	Nov 15 - Nov 25	Nov 22	239°32	117°	+01°	65	2.4	var
Dec Phoenicids (PHO)	Nov 28 - Dec 09	Dec 06	254°25	18°	-53°	18	2.8	var
Puppid/Velids (PUP)	Dec 01 - Dec 15	(Dec 07)	(255°)	123°	-45°	40	2.9	10
Monocerotids (MON)	Nov 27 - Dec 17	Dec 09	257°	100°	+08°	42	3.0	2
σ-Hydrids (HYD)	Dec 03 - Dec 15	Dec 12	260°	127°	+02°	58	3.0	3
Geminids (GEM)	Dec 07 - Dec 17	Dec 14	262°2	112°	+33°	35	2.6	120
Coma Berenicids (COM)	Dec 12 - Jan 23	Dec 20	268°	177°	+25°	65	3.0	5
Ursids (URS)	Dec 17 - Dec 26	Dec 23	270°7	217°	+76°	33	3.0	10

================================================================
Some useful glossary

Absolute magnitude

The stellar magnitude any meteor would have if placed in the observer's zenith at a height of 100 km.

Aphelion distance

Abbreviation Q, distance of greatest heliocentric separation for a body in an eccentric orbit; Q=a(1+e).

Apollo asteroids

Asteroids having semimajor axes a>1.0 au, and perihelion distances q<1.017 class="glossary-related">See also: Asteroid, Aten asteroids, Perihelion distance, Semimajor axis

Asteroid

One of a number of objects ranging in size from sub-km to about 1000 km, most of which lie between the orbits of Mars and Jupiter; also called 'minor planet'. The preliminary designations consist of the year of discovery, an upper case letter to indicate the halfmonth in that year (A=Jan 1-15, B=Jan 16-31, ..., Y=Dec 16-31, the letter I being omitted), and a second upper case letter in sequence. When this sequence of 25 letters (with I again being omitted) has been completed it is repeated and followed by a sequential number. Permanent designations consist of numbers and names, beginning with (1) Ceres, given to asteroids for which orbits are accurately determined. Names are generally proposed by the discoverer. See also: Apollo asteroids, Aten asteroids, Meteoroid Stream

Aten asteroids

Asteroids having semimajor axes a<1.0>0.983 au. See also: Apollo asteroids, Asteroid, Semimajor axis

Comet

A diffuse body of solid particles and gas, which orbits the Sun. The orbit is usually highly elliptical or even parabolic. Comets are unstable bodies with masses of the order of 10^18 g whose average lifetime is about 100 perihelion passages. Periodic comets comprise only ~4% of all known comets. Periodic comets are designated by a number, followed by 'P/' and its name. E.g. Halley's comet has the designation 1P/Halley, the parent body of the Perseids, 109P/Swift-Tuttle. See also: Meteoroid Stream

Fireball

A bright meteor with an apparent visual magnitude of -4 mag. or brighter. See also: Meteor, Meteorite, Meteoroid, Persistent train

Geocentric

Earth-centered.

Heliocentric

Sun-centered.

Inclination

Abbreviation i., in the Solar System, the angle between an orbit and the plane of the Earth's orbit (ecliptic).

Limiting magnitude

Generally denotes the faintest star visible during an observation and evaluates the quality of the sky as well as the observing technique. The magnitude of the faintest meteor visible can be different from the stellar limiting magnitude, particularly for photographic and video observations. Visual observations assume about the same limiting magnitudes for stars and meteors. See also: Photographic observations, Video observations, Visual observations

Meteor

In particular, the light phenomenon which results from the entry into the Earth's atmosphere of a solid particle from space. See also: Fireball, Meteor Shower, Meteorite, Meteoroid

Meteor Shower

A number of meteors with approximately parallel trajectories. The meteors belonging to one shower appear to emanate from their radiant. See also: Meteor, Solar longitude, Trajectory

Meteorite

A natural object of extraterrestrial origin (meteoroid) that survives passage through the atmosphere and hits the ground. See also: Fireball, Meteor, Meteoroid, Micrometeorite

Meteoroid

A solid object moving in interplanetary space, of a size considerably smaller than a asteroid and considerably larger than an atom or molecule. See also: Fireball, Meteor, Meteorite, Meteoroid Stream

Meteoroid Stream

Stream of solid particles released from a parent body such as a comet or asteroid, moving on similar orbits. Various ejection directions and velocities for individual meteoroids cause the width of a stream and the gradual distribution of meteoroids over the entire average orbit. See also: Asteroid, Comet, Meteoroid

Micrometeorite

A small extraterrestrial particle that has survived entry into the Earth's atmosphere. The actual size is not rigorously constrained but is operationally defined by the collection procedure. Micrometeorites found on the Earth's surface are smaller than 1mm, those collected in the Stratosphere are rarely as large as 50 micro-m. See also: Meteorite

Path

The projection of the line of motion of the meteor on the celestial sphere, as seen by the observer.

Perihelion distance

abbreviation q, distance of the least heliocentric separation for a body in an eccentric orbit; q=a(1-e). See also: Apollo asteroids

Persistent train

Remaining glow due to ionization in the upper atmosphere after the passage of a meteoroid. The intensity and duration depend on the meteoroid's atmospheric entry velocity, its size, and its composition. Bright fireballs occasionally caused trains visible for several minutes. See also: Fireball

Photographic observations

The meteors are captured on a photographic film or plate. The accuracy of the derived meteor coordinates is very high. Normal-lens photography is restricted to meteors brighter than about +1mag. Multiple-station photography allows the determination of precise meteoroid orbits. See also: Limiting magnitude, Video observations

Poynting-Robertson effect

A dissipative force due to the anisotropic loss of momentum by a particle through re-radiation of solar energy. This causes aphelion collaps such that a circular orbit is soon attained; thereafter the particle spirals slowly towards the Sun. Small particles (below 1cm) are most severely affected because the force varies as the reciprocal of its size.

Radiant

The point where the backward projection of the meteor trajectory intersects the celestial sphere. More generally, the point in the sky where meteors from a specific shower seem to come from. See also: Trajectory

Radio observations

Two main methods are used, forward scatter observations and radar observations. The first are easy to carry out, but deliver only data on the general meteor activity; showers cannot be associated. The last is carried out by professional astronomers. Meteor radiants and meteoroid orbits can be determined.

Semimajor axis

Abbreviation a, half the length of the major axis of an ellipse, a standard element used to describe an elliptical orbit. See also: Apollo asteroids, Aten asteroids

Solar longitude

Angular distance along the Earth's orbit measured from the intersection of the ecliptic and the celestial equator where the Sun moves from south to north. It gives the position of the Earth on its orbit and, hence, is a more appropriate information on a meteor shower's maximum than the date. See also: Meteor Shower

Telescopic observations

Monitoring meteor activity by a telescope, preferably binoculars. This technique is used to determine radiant positions of major and minor showers, to study meteors much fainter than those seen in visual observations. See also: Visual observations

Trajectory

The line of motion of the meteor relative to the Earth, considered in three dimensions. See also: Meteor Shower, Radiant

Universal Time

The local mean time of the prime meridian. It is the same as Greenwich mean time, counted from 0 hour beginning at Greenwich mean midnight.

Video observations

This technique uses a video camera coupled with an image intensifier to record meteors. The positional accuracy is almost as high as that of photographic observations and the faintest meteor magnitudes are comparable to visual or telescopic observations depending on the used lens. Meteor shower activity as well as radiant positions can be determined. Multiple-station video observations allow the determination of meteoroid orbits. See also: Limiting magnitude, Photographic observations, Visual observations

Visual observations

Monitoring meteor activity by the naked eye. Least accurate method but easy to carry out. Large numbers of observations permit statistically significant results. Visual observations are used to monitor major meteor showers, sporadic activity and minor showers down to a ZHR of 2. See also: Limiting magnitude, Telescopic observations, Video observations, ZHR

ZHR

The number of shower meteors per hour one observer would see if his limiting magnitude is 6.5mag and the radiant is in his zenith. See also: Visual observations

Resources:
http://imo.net for Glossary & Meteor Shower Calender
http://www.meteorobs.org/showers.html for Basics of Meteor

Universe @ 380,000 Years Post Big Bang

Pic1: Remodelling of Big Bang showcasing big bang to birth of first star to galaxies to universe expanding at exponential rate due to dark matter/dark energy

This post is based on NASA's release on Feb 11, 2003.

The cosmic portrait–taken by NASA’s Wilkinson Microwave Anistropy Probe–shows the universe as it looked 380,000 years after the big bang, some 200 million years before any stars or galaxies had formed.

In Layman's words: "If you stand on top of Empire State Building and observe the ground, what you see by 7th floor is a time-frame by which the stars-galaxies were born, going down (going back to the past) what you see just 2" above ground is the image of baby universe (around 380,000 years old from big bang)

The probe imaged the entire sky for a full year, producing a detailed picture of the cosmic microwave background, the afterglow of the big bang. The incomparable heat of the big bang has cooled to a mere 2.73 degrees above absolute zero, but WMAP can detect temperature variations of millionths of a degree. Within these variations were the seeds that later grew into stars, galaxies and clusters of galaxies that populate the universe today.

In other findings, WMAP pegged the age of the universe at 13.7 billion years, with an error margin of only 1 percent. It also measured the contents of the universe to consist of 4 percent ordinary matter (which make up people, planets and stars), 23 percent of an unknown and unseen material called dark matter, and 73 percent of a mysterious dark energy that acts in opposition to gravity.

Pic2: A cosmic history, illustrated above, shows the first light of the universe–the afterglow of the big bang, which the WMAP observed. This light emerged 380,000 years after the big bang. Patterns imprinted on the light, which are shown in the first ellipse, encode the events that happened only a tiny fraction of a second after the big bang. In turn, the patterns are the seeds of development for galaxies we now see billions of years after the big bang.

The light we see today, as the cosmic microwave background, has traveled over 13 billion years to reach us. Within this light are infinitesimal patterns that mark the seeds of what later grew into clusters of galaxies and the vast structure we see all around us today.

Patterns in the big bang afterglow were frozen in place only 380,000 years after the big bang, a number nailed down by this latest observation. These patterns are tiny temperature differences within this extraordinarily evenly dispersed microwave light bathing the universe, which now averages a frigid 2.73 degrees above absolute zero temperature. WMAP resolves slight temperature fluctuations, which vary by only millionths of a degree.

Theories about the evolution of the universe make specific predictions about the extent of these temperature patterns. Like a detective, the WMAP team compared the unique "fingerprint" of patterns imprinted on this ancient light with fingerprints predicted by various cosmic theories and found a match.

Pic3: WMAP

Note: WMAP is named in honor of David Wilkinson of Princeton University, a world-renowned cosmologist and WMAP team member who died in September 2002.

Resources:

1) http://science.nasa.gov/headlines/y2003/11feb_map.htm
2) http://chronicle.uchicago.edu/030220/probe.shtml

Betelgeuse

Betelgeuse is the first star (other than Sun) to be spotted by Hubble Telescope. The image was taken in ultraviolet light with the Faint Object Camera on March 3, 1995.


This is also called Alpha Orionis, or Betelgeuse, it is a red supergiant star marking the shoulder of the winter constellation Orion the Hunter (diagram at right).

Other names for this star are Betelguex, Betelgeuze, Beteiguex, or Al Mankib. Betelguese and the related names derive from the Arabic phrase Ibt al Jauzah meaning "The Armpit of the Central One".

The Hubble image reveals a huge ultraviolet atmosphere with a mysterious hot spot on the stellar behemoth's surface. The enormous bright spot, more than ten times the diameter of Earth, is at least 2,000 Kelvin degrees hotter than the surface of the star.

The image suggests that a totally new physical phenomenon may be affecting the atmospheres of some stars. Follow-up observations will be needed to help astronomers understand whether the spot is linked to oscillations previously detected in the giant star, or whether it moves systematically across the star's surface under the grip of powerful magnetic fields.

Data

• RA 05 55 10.3
• Distance (Light Years) 427 ± 92
• Dec +07 24 25
• V 0.50
• B-V +1.85
• Spectral Type M1-2Ia-Iab

Betelgeuse (also known as alpha ori) is a very large star, an M supergiant. This is because it has evolved far from the state in which stars spend most of their lives, known as the main sequence. For stars on the main sequence, which includes our Sun, there is simple proportionality between size and mass, and also a simple scaling for luminosity. For evolved stars the situation is less simple. Betelgeuse is more than 1000 times larger than the Sun, and 50000 times as luminous, but only about 20 times as massive. Most of the light from Betelgeuse comes out in the infrared, however, which is very different from the Sun. One consequence of the advanced evolutionary state of Betelgeuse is that it probably was much more massive when it was on the main sequence, and has already lost a significant fraction of its mass (probably more than half) in a stellar wind.

There are many stars that are as massive as Betelgeuse is now, and probably many that are as massive as Betelgeuse was when it was on the main sequence. Of the 100,000,000,000 (100 billion=10^11) or so stars in our galaxy , it is estimated that approximately 1% have main sequence masses greater than 30 times that of the Sun, which is where Betelgeuse may have started out. A very crude estimate is that such stars spend 1% of their lives as supergiants, which would suggest 10,000,000 stars similar to Betelgeuse in our galaxy.

In spite of this fact, there are very few stars which are visible to the naked eye which are as large as Betelgeuse. This is simply a consequence of the fact that we can distinguish bright stars in only a small fraction of the galaxy. Another one is Mira, in the constellation Cetus. Mira is probably larger than Betelgeuse, so large that it is thought that the outer layers of the star are barely held together by gravity. Mira is known to pulsate and eject its outer layers, probably in large part because of its weak gravity. Possibly the most massive known star is eta carina, which may have been 150 times as massive as the Sun when it first formed, and may be 50 - 60 times as massive as the Sun currently. In the 1830s eta carina underwent a tremendous outburst during which it became a brilliant naked eye object and ejected an amount of gas with mass approximately equal to the mass of the Sun.

It is likely that the minimum main sequence mass for a star which will eventually make a black hole is 8 - 10 times the mass of our Sun. This is quite a bit less than Betelgeuse had when it was on the main sequence, and there are many such stars in our galaxy.

Resources:
1) Tim Kallman for Ask an Astrophysicist
2) astro.uiuc.edu
3) http://hubblesite.org
4) domofthesky.com
5) Publilshed image of Betelgeuse by NASA