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Shannon Curtis
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Lived in Vancouver, BC, Canada


Shannon Curtis

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A ravishing new $120K roadster straight out of the 1940s:
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used to have a matchbox car like that,
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The Jellyfish Nebula
The Jellyfish Nebula, IC 443, is a galactic supernova remnant, in the constellation Gemini, that occurred 8,000 years ago. It is one of the best studied cases of supernova remnants, interacting with surrounding molecular clouds. IC 443 spans about 65 light-years at an estimated distance of 5,000 light-years.

The image uses the Hubble Palette. The SII data (sulfur) are mapped to the red channel, the Ha (hydrogen) to the green and the 0III (oxygen) data are mapped to the blue channel.
Taken from 1/14/2014 to 4/3/2014 in Chino Valley, AZ
Takahashi FSQ-106ED refractor
SBIG STF-8300M camera using AstroDon narrowband filters.
Losmandy G11 mount
Exposure Details:
SII 585 min.
Ha 540 min.
OIII 810 min.

Credit & Copyright: Astrophotographer Bob Franke

#Hubble   #Space   #Astronomy #Nebula #JellyFish #Supernova #Remnant #Galactic #IC443 #Gemini #Universe #Cosmos  
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Project Ara: our best look yet at Google's new modular smartphone
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Invariable Plane

One aspect of our solar system is that it is essentially a closed system.  The stars are so widely separated that it would be rare for a stray asteroid or other object from beyond the Oort cloud to enter our solar system.  This means that nearly all the rocky material orbiting the Sun now was also part of the solar system billions of years ago.  This has a few consequences, one of which is the tendency for the solar system to lie in a plane.

With a closed system, certain things are constant and unchanging.  In physics, we say they are conserved.  One of these conserved things is known as angular momentum.  In simple terms, angular momentum is a measure of the amount of rotation of a system, but in actuality it is a bit more complicated.  Angular momentum not only works for rotating bodies such as the Earth rotating on its axis, but also for collections of objects moving in different directions. For example, each of the planets orbiting the Sun has an angular momentum about the Sun.

The orbits of all the planets don’t lie within a single plane, but they are relatively close.  However, if you add the angular momenta of all the planets, (and all the asteroids, Kuiper belt, etc) you get a total angular momentum of the solar system.  Most of this angular momentum is due to the large outer planets.  Together they account for about 98% of the total angular momentum of the solar system.

This total angular momentum can be defined by a plane known as the invariable plane.  It’s invariable because the total angular momentum of the solar system is constant.  The orbits of individual planets can change due to gravitational interactions, but the invariable plane can’t change. If the Earth’s orbit shifts relative to the invariable plane due to a gravitational interaction with Jupiter, then Jupiter’s orbit must also shift.  Individual planets can gain or lose angular momentum, but they do so by taking it from or giving it to other planets.

Conservation of momentum also explains why the solar system (and other rotating systems like galaxies) tend to be planar.  Imagine an early solar system where all the different matter is moving around the proto-Sun in all directions.  All this higgledy-piggledy motion, with everything from the largest proto-planet to the smallest dust grain, has some total angular momentum.  In principle you could add up the angular momentum of every object in the early solar system, and the total would be defined by the invariable plane. As objects collide and merge, the angular momentum of the new object is equal to the sum of the originals.  As more and more objects collide, the sum of the larger and larger objects will tend toward the total angular momentum of the system. So as the planets formed, they tended to form along the invariable plane of the solar system.

This doesn’t mean that everything will tend toward the same plane.  There are, for example, comets that have an orbital plane radically different from the invariable plane.  But if you take the average of all these comets, this average is close to the invariable plane. There is also the Oort cloud on the outer edge of our solar system, which is distributed evenly around the Sun, and not in a plane at all.

But for the main planets, the invariable plane marks the plane of angular momentum that was there when the solar system began. And through the physics of  mutual interaction drew the planets close to it.
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Someone made a great point in the comments. They said that one of the kids knew perfectly who Indiana Jones was but didn't know what a cassette was.

Is it also wrong that when the kid said "so you need headphones to hear music" I was like, "yeah? is that so wrong, I don't want to hear your shitty music when I'm walking down the street"

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Gravity's Shadow

When Isaac Newton presented his theory of universal gravitation it revolutionized our view of the universe. Rather than having a separate set of laws for the heavens and terrestrial physics, universal gravity unified heaven and Earth and marked the beginning of astrophysics.  But universal gravity required a strange behavior known as action-at-a-distance.  That is, two masses separated by great distances could experience a force of attraction between them without ever being in contact with each other.  Just how that was possible wasn’t clear, and Newton’s theory provided no explanation.

In 1748  Georges-Louis Le Sage proposed a solution to this problem.  He argued that gravity wasn’t due to a mutual attraction between masses, but rather due to the interactions of particles moving through space. In the Le Sage model, the universe is filled with a sea of corpuscles (basically particles) speeding along in all directions.  A single mass would be pushed evenly in all directions, thus there would be a downward force toward its surface. Two masses in the vicinity of each other would cause an imbalance between them.  Basically, the two masses would cast “shadows” upon each other so that there would be less corpuscles in the region between them.  As a result the two masses would be pushed toward each other.

If this kind of “shadow gravity” were real, then it seems that the gravitational force between two masses should be proportional to their size, not their mass.  After all, larger objects cast larger shadows.  But Le Sage argued that masses are mostly empty space, with small clumps of matter spread throughout the object.  The greater an object’s mass, the more numerous the clumps.  Thus matter is somewhat opaque to these gravity corpuscles, but more massive objects are less opaque.  Thus more massive objects cast darker shadows, and therefore are pushed more strongly to each other.

Le Sage’s shadow gravity model was never very popular, in large part because its focus was to explain the mechanism of gravity without making any testable predictions.  Newton’s action-at-a-distance may be strange, but it works extraordinarily well as a physical theory. By the early 1900s, when Einstein developed the general theory of relativity, gravity was seen as a local effect due to the curvature of space.  Action-at-a-distance isn’t needed for gravity, and so Le Sage’s idea is generally considered a failed idea.

That hasn’t stopped some from continuing to pursue the model.  The idea shows up now and then in alternative (aka fringe) models in various forms. As evidence for their ideas, many point to an experiment known as the lunar eclipse gravity test.  If such a shadow gravity model were true, then during a total solar eclipse there should be a small shift in the strength of gravity as the moon shadows Earth from the Sun.  Curiously, there have been experiments to test for such an effect, and there may be a strange gravity shift going on.

Most of the tests focus on the motion of a Foucault pendulum during a total eclipse.  This was first studied by Maurice Allais in 1954, who noted that a pendulum shifted an extra 13 degrees during a total eclipse.  Over the next 50 years similar experiments have been done, with some showing an effect, and some not.  It is sometimes referred to as the Allais effect.  Although shadow gravity fans argue the Allais effect supports their models, but if that were the case there should also be an Allais effect during a lunar eclipse, which hasn’t been observed.  Supporters often note that Allais is a Nobel laureate, but he was awarded the Nobel in Economics, not physics.  The most modern tests for the effect using gravimeters and automated pendulums have observed no Allais effect, so even the validity of the effect is questioned.

Perhaps what’s most interesting about Le Sage’s model is how it got some ideas right.  With light, shadow effects between dust particles do produce a small net attractive force, and that force follows an inverse square relation just like gravity.  It is sometimes referred to as mock gravity.  And matter really is mostly empty space, with dense clumps of matter spread throughout an object.  We now know that these are the nuclei of atoms.

Sometimes in the pursuit of understanding we create models that are right in some ways and wrong in others.  The only way we can separate the good ideas from the bad is to keep testing them against experimental evidence.  It’s how we can move our theories out of the shadows.

Image: Georges-Louis Le Sage
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The Hubble Space Telescope takes a picture of deep space
This long-exposure image taken with NASA's Hubble Space Telescope is the deepest-ever picture taken of a cluster of galaxies, and also contains images of some of the intrinsically faintest and youngest galaxies ever detected. The photo  was released January of this year.

It amazing to think that this is just one section of the sky. Multiply this image by the millions and you have an idea of the immensity of the universe. Galaxies contain varying numbers of planets, star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Super massive black holes reside at the center of most galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy is known to harbor at least one such object.

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NASA's Kepler Telescope Discovers First Earth-Size Planet in 'Habitable Zone'
From JPL: Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun. Shown: The artistic concept of Kepler-186f is the result of scientists and artists collaborating to imagine the appearance of these distant worlds. Image credit: NASA Ames/SETI Institute/JPL-Caltech
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I'm a geek, but that's ok, I don't mind
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Vancouver, BC, Canada - Chattanooga, TN, USA - Sacramento, CA, USA - Dalton, GA
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