Posted on 02/03/2006 10:23:55 PM PST by neverdem
For those who are studying aspects of the origin of life, the question no longer seems to be whether life could have originated by chemical processes involving non-biological components but, rather, what pathway might have been followed.
—National Academy of Sciences (1996)
It is 1828, a year that encompassed the death of Shaka, the Zulu king, the passage in the United States of the Tariff of Abominations, and the battle of Las Piedras in South America. It is, as well, the year in which the German chemist Friedrich Wöhler announced the synthesis of urea from cyanic acid and ammonia.
Discovered by H.M. Roulle in 1773, urea is the chief constituent of urine. Until 1828, chemists had assumed that urea could be produced only by a living organism. Wöhler provided the most convincing refutation imaginable of this thesis. His synthesis of urea was noteworthy, he observed with some understatement, because “it furnishes an example of the artificial production of an organic, indeed a so-called animal substance, from inorganic materials.”
Wöhler’s work initiated a revolution in chemistry; but it also initiated a revolution in thought. To the extent that living systems are chemical in their nature, it became possible to imagine that they might be chemical in their origin; and if chemical in their origin, then plainly physical in their nature, and hence a part of the universe that can be explained in terms of “the model for what science should be.”*
In a letter written to his friend, Sir Joseph Hooker, several decades after Wöhler’s announcement, Charles Darwin allowed himself to speculate. Invoking “a warm little pond” bubbling up in the dim inaccessible past, Darwin imagined that given “ammonia and phosphoric salts, light, heat, electricity, etc. present,” the spontaneous generation of a “protein compound” might follow, with this compound...
(Excerpt) Read more at commentarymagazine.com ...
Current evidence indicates that the early earth had a mildly reducing atmosphere (Kasting 1993). It was probably rich in hydrogen due to the escape of hydrogen from the atmosphere being much lower than previously thought (Tian et al. 2005). Calculations of the outgassing expected from chondrites (which the earth was largely formed from) also indicate a reducing atmosphere (Thomas 2005).What D.I. doesn't like, D.I. fails to cite.
Yes. I'm finding this article to be amazingly well-written. One sentence leaped out at me from early in the article:
Before the era of biological evolution, they conjectured, there must have been an era of chemical evolution taking place in something like a pre-biotic soup.This seems like a very good way to deal with the ever-popular question that creationists are always asking -- how did life begin? The quick (and truthful) answer is that the question asks about chemical evolution, and Darwin dealt only with biological evolution.
I'm pinging Ichneumon to get his opinion on the article, before I allow myself to get even more enthusiastic than I already am.
Even Jack Chick knows that. ;)
Yes, but it doesn't have to be necessarily trial and error, although most of it is. In systems engineering, when designing trade studies to determine the best attributes, we call that limiting the trade space. We have a computer program that uses multivariate analysis to eliminate the useless combinations. We can often influence the direction that evolution takes.
He crams in swarmy detail until the article itself risks becoming irreducibly complex. He tips his hand early. He never wavers or falters until he gets where he's going. However, I'm left wondering what else he's leaving out (besides the evidence Miller and Urey were right after all about the Earth).
That's a lot to be right about. Try "... were right about the reducing atmosphere of the early Earth."
As the original quote noted, polarized light most certainly can have different effects on L and R stereoisomers (i.e. more likely to be absorbed by, and thereby disrupt bonds in, one than the other).
One might as well assert that inserting a screw into a threaded hole will have the same result whether the screw thread direction is the same as, or opposite to, the hole thread direction.
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.
The Celestial sphere
When we look up at the stars in the night sky they appear to be stationary relative to each other. As the Earth moves from one side of the Sun to the other, the displacement of those stars due to parallax is less than one second of arc even for the nearest star (Proxima Centauri). One way of looking at this is a fixed sphere of stars surrounding the Earth/Sun system. This is often referred to as the Celestial Sphere. This is why some of the ancient civilizations considered the stars to be holes in a tapestry.
Since we are talking distances and parallax, let's briefly take a moment and describe such. The more familiar term for the layman when referring to stellar distances is called a light year. This is the distance light will travel in one calendar year. For example the closest star to our Sun, Proxima Centauri, is approximately 4.22 light years from our solar system. The light we see from there today was actually generated by that sun 4.22 years ago. Astronomers use another term for stellar distance that may be not so familiar: the Parsec. A Parsec (parallax-arcsecond) is the distance needed for one astronomical unit (AU) to subtend one second of arc. An AU is the average distance from the Earth to the Sun or approximately 93 million miles, and an arcsecond is 1/60 of an arcminute, which is 1/60 of a degree. It turns out a Parsec is about 3.26 light years. Thus for an observer sitting 3.26 light years from the sun, the distance from the sun to Earth's orbit subtends one arcsecond.
Conversely, an observer on the Earth will see an object positioned one Parsec away appear to shift by up to two arcseconds over the course of a year. If one sighting is made when the line from the Sun to the Earth is 90 degrees from the line of observation, 6 months later the Earth will be on the opposite side of it's orbit. Since the radius of the Earth's orbit is one AU, the diameter is 2 AUs. This change in apparent position from different viewing locations is called parallax.
Proxima Centauri (at 4.22 Light Years or roughly 1.3 Parsecs), shows parallax of about one-and-a-half seconds of arc over the course of a year - too small to be discerned without special high-precision equipment. Most stars are much further away than Proxima Centauri, so for most practical purposes the stars are fixed - at least for periods less than a decade.
Even though it appears the stars remain in "fixed" locations in the night sky, over a period of decades and centuries the stars do move relative to each other and relative to the Earth. The star catalogue based on the epoch B1950 and the one based on the epoch J2000 would reveal minor differences due to these motions.
Another interesting item of note is that the constellations we see are made up of the brightest stars. Even in the same constellation these stars are at vastly different distances from the Earth. Some may be very bright stars that are very distant, and these may appear dimmer than closer stars that are not actually generating nearly as much light. The brightness of a star is called its magnitude. There are two ways astronomers measure magnitude: Apparent Magnitude and Absolute Magnitude.
The Apparent Magnitude is how bright a star appears to us here on the Earth. The Absolute Magnitude is how bright a star would appear if it were exactly ten parsecs away from the Earth. (Close to 33 light years).
Two notes:
1) Apparent magnitude is usually denoted with a small "m" and absolute magnitude uses a capital "M".
2) The magnitude scale is backwards of what you might think: the larger the number the fainter the object. The brightest star is Sirius with magnitude of -1.5m, while somewhat dimmer Vega is defined as 0m, and planet Venus may become as bright as -4.4m. A typical human eye can just barely see a star with a magnitude of +6m, but Earth-based telescopes may see stars as dim as +18m, and the Hubble can see stars as feint as +30m.
The Ecliptic Plane
Since the Earth is tilted (23.5 degrees) in reference to the path it sweeps out in its orbit about the Sun, this path projected onto the celestial sphere does not fall on the celestial equator. This imaginary plane is called the ecliptic. Note: This angle between the ecliptic and the equatorial plane is called The Obliquity of The Ecliptic.
This imaginary plane crosses the celestial equator in two places (called the equinoxes). The Vernal Equinox falls in the spring as the Sun appears to cross the ecliptic going north and the Autumnal Equinox falls in autumn when the Sun again crosses the ecliptic, this time going south. Note: Vernal comes from the Latin vernalis, meaning spring. Also the term equinox relates to the word equal since both day and night are close to the same, 12 hours during the equinox.
The points where this plane is the farthest above (north) and below (south) the celestial equator is called the solstices. In the northern hemisphere of the earth, the most northern point of the ecliptic is called the Summer Solstice and the southern most is called the Winter Solstice. In the Southern hemisphere of the Earth the reverse is true.
The zodiac lies along the plane of the ecliptic. Since the Earth is orbiting the Sun, the Sun appears to follow the plane of the ecliptic, making one complete circle in one calendar year. The name "zodiac" comes from the Greek meaning animal circle. In fact all of the 12 constellations of the zodiac are named after animals. Note: The path of the Moon and the other planets fall pretty much on this plane as well. Since it takes 365 days for the Earth to orbit the Sun and there are 360 degrees in a circle, the Sun moves pretty close to 1 degree per day.
Celestial Coordinates
If, on the first day of spring (the Vernal Equinox), a line is drawn from the Sun through the Earth and out to infinity, that line is said to extend to a point referred to as The First Point of Aries. (So named because at one time this line pointed to the first star in the constellation of Aries.)
The celestial sphere is tied to the Earth for its coordinate system. Project the Earth's equator out to infinity and you have the equator of the celestial sphere. Likewise the north and south poles of the Earth points to the north and south poles of the celestial sphere respectively. This makes it very easy to map the sky referenced to the Earth. This coordinate system is called the Equatorial Coordinate System. It ties in closely with our own geographic coordinate system here on the surface of the Earth.
Note, however, the geographic coordinate system is fixed upon the surface of the Earth (Lat-Long) -- so it rotates with the rotation of the Earth. The celestial coordinate system is fixed to the celestial sphere and appears to rotate due to the Earth's rotation. The equivalent of "latitude" in the celestial sphere (the angle of an object above or below the celestial equator) is called declination, with zero being on the equator. (This is pretty easy to relate to, since the celestial's equator and poles appear to be fixed like our own earth.) The celestial sphere's analog to "longitude", called right ascension, is not a "fixed" reference to the Earth: it is fixed to the stars instead, thus rotating every 24 hours. Instead of using degrees, right ascension is measured in hours. The Vernal Equinox is used as the zero reference for the right ascension. Since there are 360 degrees in a circle, the Earth rotates about 15 degrees every hour, so every hour of right ascension is equivalent to 15 degrees.
A declination of zero is on the equator and a right ascension of zero is at the Vernal Equinox. So on the first day of spring, when the Earth's equator lines up with the line to the First Point of Aries, the Vernal Equinox will have the coordinates of 0 degrees and 0 hours. This has come to define the center point for an Equatorial Sky Chart.
How was all this formed?
We will first start out with the evolution of a single, low mass star from a molecular cloud to fusion and planetary accretion
Although dust and gases are found throughout interstellar space, star formation is a relatively rare event with perhaps only 10 percent of interstellar medium actually being converted into stellar mass. Interstellar space contains roughly about 10 hydrogen atoms per cubic meter at approximately 100 to 106 K. In pockets of non-homogeneous molecular gas and dust, the densities of matter may be as high as 104 to 106 atoms per cubic meter (contrast this with atmospheric air at STP ¡Ö 5.3 x 1025 atoms per cubic meter). Particulate matter within these regions is thought to include not only atomic and molecular hydrogen (H2), but also helium, carbon monoxide (CO), water ice (H2O), alcohols, ammonia (NH3), formaldehyde (HCHO), formic acid (HCOOH), methane (CH4), and other organics such as aliphatic hydrocarbons. Dust particles effectively block ultraviolet radiation from nearby stars, thus decreasing temperatures within these regions to only about 10 to 20 K.
Radio astronomers use CO emissions at 1.3 and 2.6 mm to identify molecular hydrogen (H2) in these cold molecular clouds. H I regions consist primarily of neutral atomic hydrogen (H) gas with densities of up to 107 atoms per cubic meter at temperatures around 100 K, and are detected from 21-cm emissions generated by the quantum spin flip of individual hydrogen electrons. H I regions may also be detected by Alpha Lyman H-absorption bands. In contrast, very hot H II and He III regions (up to 10,000 K) within glowing emission nebulae close to O and B spectral type stars (such as the Lagoon Nebula) are detected via infrared radiation.
Note: Super geek alert #1:
The accepted view of star formation requires that an influx of non-thermal energy (shock wave or turbulence) initiate the collapse of molecular clouds. However, some researchers believe that these clouds can become stellar nurseries simply because cooler temperatures allow matter to move more slowly, allowing tiny gravitational and ionic forces between atoms to form complex molecules, leading to gravitational collapse.
Irrespective of the initial mechanism, areas of accumulated matter grow and coalesce, eventually forming a center of mass around which particulate matter and gases orbit, often colliding with other particles or the center of mass itself. As the mass contracts under continuing gravitational attraction, the core begins to heat and infrared radiation is released. Rotational velocity also increases, conserving outward angular momentum while allowing a continuous inward flow of material. The orbiting mass begins to take on a flattened disk-like shape about the core, which is now more appropriately referred to as a prestellar core or protostar. The protostar may have densities of up to 107 atoms per cubic meter at this stage in its evolution (newly formed stars have observed densities of about1022 atoms per cubic meter). Interior core temperatures may reach 150,000 K, with surface temperatures of about 3500 K as outward thermal pressure increases to compensate for the inward pull of gravity. At this point, the protostar will appear on a Hertzsprung-Russell diagram as a cool but bright star, as luminosity is still dependant upon gravitational collapse.
As contraction continues, particles that are outside the accretion disk, but still under the influence of gravitational attraction from the protostar, will be drawn into more extreme sinusoidal orbits in and out of the plane of the accretion disk. The chance that these extra accretion disk particles will collide with particles within the disk increases not only with increased density and thickness of the disk, but also with a decreased angle of incidence relative to the plane of the disk. Most particles will ultimately become part of the protostar, but some will enter into a variety of orbits within the accretion disk plane depending on their relative velocities, often forming additional regions or bands of increased density from which protoplanets may later accrete.
While the protostar stage of development may only take a few years, the pre-main sequence stage may take tens of millions of years because continued contraction, accretion and heating of the stellar core proceeds slowly.
Early pre-main sequence stars are often referred to as T Tauri stars. In these very young stars, an excess of ultraviolet radiation is released as dipolar magnetospheric accretion columns form, slowing the rotational velocity of the star in relation to the disk, and transferring mass directly from the disk to the poles of the young star. Accretion rates for these stars have been estimated to be from about 2 x 10-8 to 10-7 the mass of our Sun per year. However, mass is also simultaneously ejected from these stars perpendicular to the circumstellar disk along magnetic field lines in very narrow bipolar jets or pulses of material, possibly a mechanism for reducing excess angular momentum. T Tauri stars are hotter but not as bright as protostars, and will appear on a Hertzsprung-Russell diagram closer towards the main sequence as late F through early K spectral types.
Once the internal temperatures of the young star reach about 1 million Kelvin, the proton-proton chain reaction begins, first fusing two protons into one deuterium plus a positron and a neutrino [equation 1].
[1] 1 H + 1 H ->2 H + positron (e+) + neutrino
The positron almost immediately encounters an electron, and the particles annihilate each other, producing two gamma rays. These gamma rays will ultimately migrate to the stellar surface where they will each be emitted as about 200,000 photons of visible light [equation 2].
[2] e+ + e- -> 2 gamma rays
Deuterium created via the reaction represented by equation 1 reacts with a proton to create one helium-3 plus another gamma ray [equation 3].
[3] 2 H + 1 H -> 3 He + gamma ray
When stellar core temperatures reach 10 million Kelvin, two helium-3 atoms will be fused into one helium-4 atom plus two protons [equation 4], an event that marks the transition to the main-sequence phase of stellar evolution, when energy produced is no longer due to gravitational collapse, but by nuclear fusion.
[4] 3 He + 3 He -> 4 He + 21 H
Main sequence stars are typically very stable because of hydrostatic equilibrium, where the forces between continued gravitational collapse equal internally generated thermal pressures. Typically, a low-mass star will continue in the main sequence for about 90% of its lifetime, slowly converting hydrogen into helium for several hundred million to several billion years until the supply of hydrogen is exhausted.
Planetary formation from stellar accretion
A model of early solar system formation (and there is evidence supporting such) describes that metal, such as Nickel-iron, rock, and ice condensed out from the accretion disk created as our solar system formed. The metals condensed out first (this is why many of the asteroids are Nickel-iron) Followed by rocky material and ice. These tiny particles then collided creating small boulders and asteroids.
Once these small asteroids and boulders have enough mass, gravity becomes the driving force. Thusly the planets and moons are formed. However, since Jupiter is so large and the total mass of the asteroid belt is so tiny, the material forming the asteroid belt never was "allowed" to form a small planet or moon because of the gravitational perturbations from Jupiter. Remember the asteroid belt has less mass than 1 tenth of our moon.
Finally the solar wind from the newly formed star (our sun) would blow all of the remaining gas into interstellar space leaving us with the planets, moons, comets, asteroids, etc. circling our little star.
Note: This is a really simplified version. There is much (volumes of data) I did not include.
Since we are talking about the Solar System, I thought I would add a little data about our solar system: :-)
All planets move in ellipses. A planet that moves in a perfectly circular orbit is actually an ellipse with its eccentricity (e) = 0, a parabola has e = 1 and a hyperbola the e > 1, thusly, the closer to zero the planets eccentricity, the more circular its orbit.
For the planets, the furthest point from the sun in its orbit is called aphelion and the closest is called perihelion.
All of the planetary distances from the Sun are measured in Astronomical Units (AUs). One AU is the average distance from the Earth to the Sun, which is approximately 93,000,000 miles.
Mercury: e = 0.2056 and its AU = .39
Venus: e = 0.0068 and its AU = .72
Earth: e = 0.0167 and its AU = 1
Mars: e = 0.0934 and its AU = 1.52
Jupiter: e = 0.0483 and its AU = 5.20
Saturn: e = 0.0560 and its AU = 9.54
Uranus: e = 0.0461 and its AU = 19.18
Neptune: e = 0.0097 and its AU = 30.06
Pluto: e = 0.2482 and its AU = 39.44
If you notice only two planets have a high eccentricity; Mercury and Pluto. Only one of them cross the mean distance of another planet from the Sun and that is Pluto and Neptune. Briefly Pluto is closer to the Sun than Neptune when its orbit is at perihelion.
The eccentricity of our planet's orbit is mild; aphelion and perihelion differ from the mean Sun-Earth distance by less than 2 percent. In fact, if you drew Earth's orbit on a sheet of paper it would be difficult to distinguish from a perfect circle and that is with e = 0.0167. As for the perfect circle, there never will be a perfect circle with the orbital elements. Remember the other planets are also "tugging" on each other. I brought up the perfect circle to show that a circle is a very special type of ellipse. The reason for that was that when we see ellipses in our mind, we see really elongated structures. Also when you look at a "map" of the solar system, they usually put it in a somewhat side perspective which exaggerates the appearance of the ellipse.
Most of the planets are so close to circles that on a piece of paper they would look just that. Again, the only two that would be even readily noticeable would be Mercury and Pluto.
For satellites orbiting the Earth, we have an added component of not only the atmospheric drag but the solar wind as well. To even further the complication our Earth is not a perfect sphere and has natural gravity wells due to the distribution of the landmasses and that it is an oblate spheroid instead of a perfect sphere (the difference is only about 15 miles between the equator and the poles). One more rub is that with long term measurements taken using a satellite in orbit (the LAGEOS), the Earth is very very slowly re-rounding itself out over time.
The other thing that is not readily apparent from most solar system maps is just how far apart the planets really are and also how tiny they are with reference to the solar system.
Enter the 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 traveling at different relative velocities due to 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 an increased red shift for distant objects than for nearby objects.
This enables us to plot the position of the intervening neutral hydrogen between us and other stellar objects.
Note: Super geek alert #2:
Radio astronomers use temperature to describe 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 is lowered, 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 point of the sky and says 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).
So, here's the rub. Not only does the source that is of interest to the radio astronomer emit thermal radiation but also both the local environment (ground, atmosphere, etc) and the equipment (antenna, amplifiers, cables, receiver, etc) being used to make the measurements. To accurately observe and measure the distant sources, the radio astronomer must subtract all of the local environment and detection equipment noise additions.
In 1963, Arno Penzias and Robert Wilson were working with a horn antenna trying to make it work with as high efficiency as 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.
Stars Visible from Earth
If you add up all of the stars that are visible from everywhere on the globe this roughly 6000 stars are visible to the naked eye, globally speaking. From any given location on a single night, about 2,500 are visible to the discerning eye. Under bright city lights, the quantity of stars visible to the unaided eye can drop to mere dozens.
Our Sun has an intrinsic or absolute magnitude of about 5. This is the apparent magnitude our Sun would have if it were 32.6 light years away. A star 100 times brighter would have a magnitude of 0; a star 10000 times brighter would have a magnitude of -5; a star 1000000 (i.e. a million) times brighter would have a magnitude of -10.
With the Hubble telescope, using an exposure time of several hours, one can see stars to about 30th magnitude. This is about 10 billion times fainter than our Sun, if it were 32.6 light years away. The brightness of any object falls off as the square of the distance from the observer, so the Hubble telescope could just see our Sun if it were 3.26 million light years away. If you were to replace our Sun with a star a million times brighter, it could be seen about a thousand times further away, i.e., about 3 billion light years.
Since this estimate is only for the very brightest stars, and since the distance I obtained is still less than the size of the visible Universe (about 15 billion light years), there are surely many faint stars at great distances which we cannot see.
On to the Earth-Sun system
It takes one year for the Earth to rotate around the Sun one time and 24 hours to rotate on its axis. Think about this relationship. Not only is the Earth revolving on its axis, it is in motion about the Sun. (I know this is really basic grade school stuff, however, it will help in visualizing the concepts I am about to explain) Therefore the Earth moves 1/365th of its orbit about the Sun every day.
Ok, here is where that visualization will come in handy. Since a "day" is described by one complete rotation of the Earth on its axis, this equates from noon to noon (when a point on the Earth is directly pointed at the Sun). The term for this is called the Mean Solar Day. But here is the rub; the Earth has moved through 1/365th of its orbit during this period of time we called a day. Because the Earth has moved over a tiny bit from where is was the day before, it must rotate a tiny bit more to have the same spot facing the Sun at noon. This tiny bit is slightly less than one degree (the Earth's orbit completes 360 degrees in 365 days). Thus the Earth actually rotates almost 361 degrees, not just 360, to complete a mean solar day.
Now let us think of this celestial sphere we have been chatting about. Remember the stars appear fixed in one location (at least on a daily basis). This means that one complete revolution of the Earth referenced to a star does not take that little bit of extra time to be over the same spot on the Earth. This "day" is referred to as a Sidereal Day. It takes approximately four extra minutes for the Earth to have the Sun over the same location on the Earth than a star.
This is the difference between a Sidereal Day (23 hours, 56 minutes) and a Mean Solar Day (24 hours).
Also the Earth is tilted on its axis from the plane of the ecliptic by 23.5 degrees. That tilt causes the North Pole to be currently pointed towards Polaris. As the Earth moves around the sun its pole stays pointed at Polaris. This is the cause of the seasons we experience. Note. This tilt varies back and forth from 21.6 degrees to 24.5 degrees approximately every 41,000 years.
There is also a precession of our pole and it sweeps a complete circle in the sky (think of the Earth as a top wobbling as it rotates) about every 26,000 years. (Hard to explain without a diagram). This gives us different pole stars as the north pole of the Earth sweeps out a circle on the celestial sphere.
There are also a number of other motions that must be taken into consideration over the years, such as the precession of the aphelion. Our Earth's orbit around the Sun is not a perfect circle. It is an ellipse with the closest point of the orbit called perihelion and the furthest point called aphelion. Currently perihelion occurs in early January, and aphelion falls in early July. However, this is not always the case. The aphelion and perihelion change over the centuries and sweeps thru the calendar year with a periodicity of around 22,000 years. By the way, the amount a circle is "squished" (not much of a scientific term :-) ) to create an ellipse is called its eccentricity. If the eccentricity is equal to zero the orbit will be a perfect circle (also known as a degenerate elipse). An eccentricity between zero and one, not inclusive, describes the eliptical path of an orbit - a highly eccentric orbit has eccentricity close to one. In the case of eccentricity equal exactly to one, the path is a parabola, and eccentricity greater than one describes a hyperbola. Although natural forces tend to circularize most orbits over time, achieving an eccentricity of exactly zero is extremely unlikely in nature.
The eccentricity of Earth's orbit is very small. However, even this changes over time. Its eccentricity varies periodically about every 100,000 years. There are also other motions effecting the orbit, caused by the Moon, Jupiter and the Sun: these are called Nutations. One of the major nutations has a period of 18.6 years.
Since we are now talking about orbiting bodies, let us digress just a wee bit further and briefly talk about orbits
There are different sizes and shapes of orbits. We use the term Semi-Major Axis to measure the size of an orbit. It is the distance from the geometric center of the ellipse to either the apogee or perigee (The highest (apo) and the lowest (peri)). Apoapsis is a general term for the greatest radial distance of an Ellipse as measured from a Focus. Apoapsis for an orbit around the Earth is called apogee, and apoapsis for an orbit around the Sun is called aphelion.
Periapsis is a general term for the smallest radial distance of an Ellipse as measured from a Focus. Periapsis for an orbit around the Earth is called perigee, and periapsis for an orbit around the Sun is called perihelion.
The terms Gee and Helios comes from the Greek words "Ge" (earth) and "Helios" (Sun) respectively.
First lets talk a bit about "where it is". An orbit is a nothing more than an object falling around another object. Both Kepler and Newton came up with a set of laws that describe this phenomenon.
Kepler's three laws of planetary motion:
1) The orbit of a planet is an ellipse with the sun at one of the foci.
2) The line drawn between a planet and the sun sweep out equal areas in equal times.
3) The square of the periods of the planets is proportional to the cubes of their mean distance from the sun.
So what is that telling us? In a nutshell, all orbits are ellipses, the close to the body you are orbiting the faster you go (e.g. if you have a highly elliptical orbit the satellite or planet's velocity will increase as it approaches the object being orbited and decrease as it get further away)
These laws not only apply to planets and satellites, but to any orbiting body.
Note: Super geek alert #3:
For an orbiting body this is not entirely correct. It turns out that both bodies end up orbiting a common center of mass of the two-body system. However, for satellites, the mass of the Earth is so much greater than the mass of the satellite, the effective center of mass is the center of the Earth.
Newton's three laws (and law of gravitation):
1) The first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. (Commonly known as inertia)
2) The second law states that force is equal to the change in momentum (MV) per change in time. (For a constant mass, force equals mass times acceleration F=ma)
3) The third law states that for every action there is an equal and opposite reaction. In other words, if an object exerts a force on another object, a resulting equal force is exerted back on the original object.
Newton's law of gravitation states that any two bodies attract one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Note: Super geek alert #4:
Actual observed positions did not quite match the predictions under classical Newtonian physics. Albert Einstein later solved this discrepancy with his "General Theory of Relativity". There are four classical "tests" that cemented General Relativity:
1) In November of 1919, using a solar eclipse, experimental verification of his theory was performed by measuring the apparent change in a stars position due to the bending of the light buy the sun's gravity.
2) The changing orientation of the major axis of Mercury not exactly matching classical mechanics.
3) Gravitational Redshift
4) Gravitational Time Dilation
So what is all this trying to tell us? Planets, satellites, etc orbit their parents in predictable trajectories allowing us to "know" where they will be at any given time. A set of coordinates showing the location of these objects over a period of time is called its ephemeris.
This is a good spot to digress into laws and theories:
Here is my own example of gravity:
A little history here:
Newton’s Law of Universal Gravitation
“Every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of the separation between the two objects.”
F=Gm1m2/r2
Where:
F equals the gravitational force between two objects
m1 equals the mass of the first object
m2 equals the mass of the second object
R equals the distance between the objects
G equals the universal constant of gravitation = (6.6726 )* 10-11 N*m2/kg2 (which is still being refined and tested today)
(BTW this is a simple form of the equation and is only applied to point sources. Usually it is expressed as a vector equation)
Even though it works well for most practical purposes, this formulation has problems.
A few of the problems are:
It shows the change is gravitational force is transmitted instantaneously (Violates C), assumes an absolute space and time (this contradicts Special Relativity), etc.
Enter Einstein’s General Theory of Relativity
In 1915 Einstein developed a new theory of gravity called General Relativity.
A number of experiments showed this theory explained some of the problems with the classical Newtonian model. However, this theory like all others is still being explored and tested.
From an NSF abstract:
“As with all scientific knowledge, a theory can be refined or even replaced by an alternative theory in light of new and compelling evidence. The geocentric theory that the sun revolves around the earth was replaced by the heliocentric theory of the earth's rotation on its axis and revolution around the sun. However, ideas are not referred to as "theories" in science unless they are supported by bodies of evidence that make their subsequent abandonment very unlikely. When a theory is supported by as much evidence as evolution, it is held with a very high degree of confidence.
In science, the word "hypothesis" conveys the tentativeness inherent in the common use of the word "theory.' A hypothesis is a testable statement about the natural world. Through experiment and observation, hypotheses can be supported or rejected. At the earliest level of understanding, hypotheses can be used to construct more complex inferences and explanations. Like "theory," the word "fact" has a different meaning in science than it does in common usage. A scientific fact is an observation that has been confirmed over and over. However, observations are gathered by our senses, which can never be trusted entirely. Observations also can change with better technologies or with better ways of looking at data. For example, it was held as a scientific fact for many years that human cells have 24 pairs of chromosomes, until improved techniques of microscopy revealed that they actually have 23. Ironically, facts in science often are more susceptible to change than theories, which is one reason why the word "fact" is not much used in science.
Finally, "laws" in science are typically descriptions of how the physical world behaves under certain circumstances. For example, the laws of motion describe how objects move when subjected to certain forces. These laws can be very useful in supporting hypotheses and theories, but like all elements of science they can be altered with new information and observations.
Those who oppose the teaching of evolution often say that evolution should be taught as a "theory, not as a fact." This statement confuses the common use of these words with the scientific use. In science, theories do not turn into facts through the accumulation of evidence. Rather, theories are the end points of science. They are understandings that develop from extensive observation, experimentation, and creative reflection. They incorporate a large body of scientific facts, laws, tested hypotheses, and logical inferences. In this sense, evolution is one of the strongest and most useful scientific theories we have.
Soory if my post was off topic. was an addition to my earlier one.
Excellent.
Discovered by H.M. Roulle in 1773, urea is the chief constituent of urine.
Wrong. Water is the chief constituent of urine. Duh!
The bases are nitrogenous because their chemical activity is determined by the electrons of the nitrogen atom, and they are bases because they are one of two great chemical clans—the other being the acids, with which they combine to form salts.
This is chemical nonsense. They are nitrogenous because they contain nitrogen; it has nothing to do with 'chemical activity'.
Proteins are formed from the alpha-amino acids, of which there are twenty in living systems.
Nope. There are far more than 20 alpha amino acids in living systems.
It was Francis Crick who in 1957 first observed that this was most unlikely. In a note circulated privately, Crick wrote that “if one considers the physico-chemical nature of the amino-acid side chains, we do not find complementary features on the nucleic acids. Where are the knobby hydrophobic . . . surfaces to distinguish valine from leucine and isoleucine? Where are the charged groups, in specific positions, to go with acidic and basic amino acids?”
It turns out Crick may have been wrong. There does indeed to be a specific interaction between triplet codons and amino-acid for which they code. This may be a molecular fossil that predates tRNA. No one has ever seen a ribozyme able to undertake chemical action without a suite of enzymes in attendance.
This is quite simply false.
The nucleic acids cannot directly recognize the amino acids (and vice versa), but they cannot directly replicate or transcribe themselves, either.
Again, this is false. There is now strong experimental evidence that RNA triplets do recognize the specific amino acids they code for. And self-replicating ligase ribozymes have been discovered.
It's also a shame to see one more rehash of the same tired and specious probabilistic arguments, and the same argument from incredulity.
Discovered by H.M. Roulle in 1773, urea is the chief constituent of urine.
Wrong. Water is the chief constituent of urine. Duh!
The bases are nitrogenous because their chemical activity is determined by the electrons of the nitrogen atom, and they are bases because they are one of two great chemical clans—the other being the acids, with which they combine to form salts.
This is chemical nonsense. They are nitrogenous because they contain nitrogen; it has nothing to do with 'chemical activity'.
Proteins are formed from the alpha-amino acids, of which there are twenty in living systems.
Nope. There are far more than 20 alpha amino acids in living systems.
It was Francis Crick who in 1957 first observed that this was most unlikely. In a note circulated privately, Crick wrote that “if one considers the physico-chemical nature of the amino-acid side chains, we do not find complementary features on the nucleic acids. Where are the knobby hydrophobic . . . surfaces to distinguish valine from leucine and isoleucine? Where are the charged groups, in specific positions, to go with acidic and basic amino acids?”
It turns out Crick may have been wrong. There does indeed to be a specific interaction between triplet codons and amino-acid for which they code. This may be a molecular fossil that predates tRNA. No one has ever seen a ribozyme able to undertake chemical action without a suite of enzymes in attendance.
This is quite simply false.
The nucleic acids cannot directly recognize the amino acids (and vice versa), but they cannot directly replicate or transcribe themselves, either.
Again, this is false. There is now strong experimental evidence that RNA triplets do recognize the specific amino acids they code for. And self-replicating ligase ribozymes have been discovered.
It's also a shame to see one more rehash of the same tired and specious probabilistic arguments, and the same argument from incredulity.
;-)
One complaint: "Note: Super geek alert #1:" isn't really going tio get anyone's attention anymore. Many FR threads contain "super greek alerts" -- I think you'll need to move on MEGA-GEEK ALERTS, UBER-GEEK ALERTS, and GIGA-GEEK ALERTS if you expect to impress anyone anymore.... think of it as a form of "inflation"...
The molecules themselves are randomly oriented. Bonds are broken by the correct frequency of light(E) on particular bonds, not the whole molecule. The interaction of light with the whole molecule, which is involved in circular polarization, does not break bonds. Any freauency of circularly polarized light is effected, by D, or L molecules. Either the light passes, or it's reflected. It will either give the molecule some angular momentum, or give it some linear momentum. In either case if the amplitude of the wave is sufficient that the momentum results in bond breaking, the temperature is high enough that no difference in destruction of either D, or L will be notable.
"One might as well assert that inserting a screw into a threaded hole will have the same result whether the screw thread direction is the same as, or opposite to, the hole thread direction."
The light either passes, or it is reflected.
Also, the proteins didn't come from space.
From reading Berlinski's books and articles, I would assume that he is just unaware.
Berlinski is an awful writer. I read two of his books; both were poorly written and uninformative.[snip link to duplicate thread]
From a Mathematical Reviews comment about another of Berlinski's books (Newton's gift): "But what is said of Newton's mathematics has only a weak connection with Newton's texts."
39 posted on 03/09/2005 5:01:17 PM EST by Doctor Stochastic
It seems fair to say that Berlinski's most notable "achievement" appears to be his indefatigable talent for writing poorly in multiple disciplines.
Excellent.
Award yourself another Corvette.
If you were truly an inquiring mind (I presume that's what you meant by "Enquiringly") , you would have discovered by now the basic datum that the Theory of Evolution has nothing to do with and says nothing about the ORIGINS of life. It discusses the origins of VARIETIES of life from the original life forms.
I apologize for the caps but this simple and obvious point needs to be repeatedly pounded into some brains.
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