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Chris Dolan
Works at Sony Creative Software
Attended University of Wisconsin-Madison
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Chris Dolan

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This is a great video that demonstrates what causes star trails (the rotation of the Earth, accumulating starlight at different positions in a photo)
 
This sequence shows you how a star trail photo is made. In the bad old days you'd have to keep the shutter open the whole time, but today far better results are achieved by "stacking" multiple short exposures into final image with trails. It also means you can animate the sequence like this, so for the one session you get the star trail photo, the animation of the earth rotating, and the animation of the frames being added together to build the star trail shot. Neat huh? Trippy music also by me, just a snippet of an unfinished thing I started. #astrophotography
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Auralnauts are my favorite youtube comedy group. Their Boston Dynamics video is brilliant and their Star Wars parodies are very funny.
 
Star Wars? Check. Masked villain? Check. Enjoy
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"To measure the new type of optical momentum and force, they used an extremely sensitive nano-cantilever, capable of femtoNewton resolution—meaning it could measure a force even smaller than the force gravity exerts on a single bacterium"

Wow! We've known for a long time that light has momentum in the direction it shines (solar sails wouldn't work without it, and you can see it with your eyes with a radiometer -- https://www.youtube.com/watch?v=a3H3ylt5F7E). But there's also perpendicular momentum carried by highly polarized light.

I wonder if this could be used to steer solar sails from afar??
 
Scientists have for the first time obtained direct measurements of the extraordinary spin momentum of light!

"Ever since Kepler's observation in the 17th century that sunlight is one of the reasons that the tails of comets to always face away from the sun, it has been understood that light exerts pressure in the direction it propagates. Radiation pressure is produced by the momentum carried by light, and it plays a crucial role in a variety of systems, from atomic to astronomical scales.

In a recent theoretical paper, a group from the RIKEN Center for Emergent Matter Science in Japan showed that momentum density in non-uniform optical fields has an unusual component, which is orthogonal to the propagation direction of light and is proportional to the optical spin, which means the degree of circular polarization. They predicted that this spin momentum would produce a transverse spin-dependent optical force, a few orders of magnitude weaker than the usual radiation pressure.

Now, based on the theoretical work, a group from RIKEN, the University of Bristol, and other institutions have used an extremely precise technique to experimentally verify that light does in fact exert the extraordinary perpendicular force, which is determined by the polarization of the light. The research has been published in Nature Physics."

Read more at: http://phys.org/news/2016-04-physicists-enigmatic-momentum.html

The study: Direct measurements of the extraordinary optical momentum and transverse spin-dependent force using a nano-cantilever, Nature Physics, http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3732.html

Image: Credit: Petr Kratochvil/public domain

#science   #light #physics
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Wes
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This is a really pleasant and concise summary of today's HTTP/HTTPS performance problems and solutions. I've read all of this before, but never in such a tidy package.
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Very pretty picture!
 
NGC 7635 - Hubble Sees a Star 'Inflating' a Giant Bubble

In this image taken by the Hubble Space Telescope you can see the Bubble Nebula (NGC 7635, Caldwell 11). It is an emission nebula located in the constellation of Cassiopeia (https://goo.gl/hSPP6L), about 7,100 light-years away from Earth. The nebula is 7 light-years across.

SAO 20575 (BD+60 2522https://goo.gl/KVzJx3), the central star of the nebula, is about 45 times more massive than our Sun. Gas on the star gets so hot that it escapes away into space as a "stellar wind" (https://goo.gl/Z9Sotn) moving at over 4 million miles per hour. The star is about 4 million years old, and in 10 million to 20 million years, it will likely detonate as a supernova (https://goo.gl/VhJNhj). In this image you can see the star within the bubble at the 10 o'clock position. 

The Bubble Nebula was discovered in 1787 by the British astronomer William Herschel (https://goo.gl/E9YsKH).

More information here:
http://hubblesite.org/newscenter/archive/releases/2016/13/image/a/
https://en.wikipedia.org/wiki/NGC_7635

What is an emission nebula?

An emission nebula is a cloud of ionized gas (often by ultraviolet radiation from nearby stars), emitting light of various colors. More information here:
https://en.wikipedia.org/wiki/Emission_nebula
https://en.wikipedia.org/wiki/H_II_region

Image credit: NGC 7635 NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

My Astronomy/Astrophysics collection recently surpassed 145,000 followers, I would have never expected that much interest, thanks to all of you! If you haven't already, maybe also try my Space/Space Technology collection here https://goo.gl/5KP0wx , or circle me +Pierre Markuse to get all of my posts which usually are science-related.

#science   #astronomy   #ngc7635   #caldwell11   #bubblenebula   #emissionnebula   #hiiregion   #space   #hubble   #hst  
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Just good
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Hahaha! A new funding model for science. "If @NERCscience have any sense you will not only announce #BoatyMcBoatface the winner but also unveil his logo and merchandise plans"
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This is a nicely composed highlight reel of four years of SpaceX progress.
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Warp drive to the rescue!
 
The Incredible Shrinking Universe

The Universe is getting smaller. Not the observable universe, which is currently a sphere about 93 billion light years across and increasing all the time, but the much smaller portion that we could ever hope to reach. Since the Universe is expanding, our cosmic playground is shrinking all the time.

If the Universe weren’t expanding, then the size of the observable universe would simply depend on its age. As the years go by, ever more distant light would be able to reach us. Likewise, we would be able to travel anywhere in the Universe given enough time. Even at speeds approaching that of light it might take billions of years, but the only limiting factor is time. But the Universe is expanding. It’s not that galaxies are racing away from some point in space, but rather that space itself is expanding, and that makes a big difference.

Since space itself is expanding, the more distant an object, the faster it seems to be moving away from us. We measure cosmic expansion in terms of the Hubble parameter, which is about 20 km/s per million light years. This means that two points in space a million light years apart are moving away from each other at 20 kilometers each second. Two points 10 million light years apart are moving away at 200 km/s, and so on. Because of this, if you consider two points far enough apart, they will be moving away from each other faster than the speed of light. The speed of light is about 300,000 km/s, which, given our current Hubble constant is the separation speed for two points 15 billion light years apart. This is known as the Hubble radius. Anything outside that radius is impossible for us to reach, even if we could travel toward it at the speed of light.

Some of you might protest, since you’ve been told numerous times that nothing can travel faster than light. The catch is that a galaxy 16 billion light years away isn’t actually traveling faster than light. What’s happening is that the expansion of space between us and the distant galaxy is increasing the distance between us faster than the speed of light. That subtle difference is also why we can see things that are farther away than 15 billion light years.

Because of cosmic expansion, the whole idea of galactic distance depends on your definition. As light leaves a galaxy to travel in our direction, space is expanding all along its journey. This not only causes the light to redden (known as the cosmological redshift) it makes the journey longer. All the while, the galaxy is moving even farther away. For light from the most distant galaxies, the light we observe has traveled for more than 13 billion years. When the light began its journey, its galaxy was only 3.4 billion light years away. Now the galaxy is 29 billion light years away. We can see such distant galaxy even though we’ll never reach them.

Since the observable universe is about 42 billion light years in radius, and the Hubble radius is about 15 billion light years, that means about 97% of the observable universe is beyond our reach. Furthermore, since space continues to expand, galaxies that are currently within reach will eventually move beyond the Hubble radius. Our galaxy is part of a cluster of galaxies known as the local group. It is about 10 million light years across and contains about 50 galaxies. Together they are close enough that their gravity will cause them to collapse toward each other despite cosmic expansion. But more distant clusters are so far away that cosmic expansion will win in the end. In perhaps a hundred billion years our local group will have collapsed into a single large galaxy, and the rest of the Universe will have moved forever out of reach.

Most of the universe we can observe is forever beyond our reach.
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+Kevin Fan I used to be an astronomer. I have never been an astrologist.
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This is a big deal for Android M and N: an app developer can declare that their app always wants to use HTTPS and the OS will help to enforce that against accidental downgrades to HTTP. It's so easy to introduce an accidental http:// URL in your API, especially if your server communication use the HATEOAS style of REST where the server provides a lot of the URLs to the client at runtime instead of hard-coding them.
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This is a fascinating theory: the solar system used to have a huge planet between the Sun and Mercury. It cleared out debris from the inner solar system, leaving Mercury, Venus, Earth, and Mars stunted and starved for matter. Then orbital migration of Jupiter and Saturn stole its angular momentum and landed it in the Sun.

I haven't read the original paper (yet) so I don't know if this is just a speculative theory or if there are orbital simulations that study the feasibility of this idea.
A Super-Earth may have formed in our Solar System's earlier days, and then been destroyed by the Sun.
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Na man
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I love topics like this. Two different experimental approaches that try to measure the half life of free neutrons yield incompatible answers. The reconciliation of the two numbers might be some fascinating new physics, but nobody knows yet.

This is a reminder that there are a lot of things we can't measure directly but instead measure by proxy (how many neutrons convert to protons per second? counting protons is an indirect measure, not a direct one). A huge amount of astronomy relies on proxy measurement: we can't see exoplanets, for example, but can only measure their effects on their host stars. A lot of thought goes into evaluating the quality and biases of those proxies, but there's always some assumption and interpretation involved.
 
The Strange Case Of Decaying Neutrons

A few days ago I wrote about how different measurements of the Hubble parameter gave results that didn’t quite agree. It’s not the only example of such an experimental disagreement. In fact, one of the biggest disagreements involves one of the most common particles in the Universe: the neutron.

The nuclei of atoms are comprised of protons and neutrons. By all observations, protons are stable and don’t radioactively decay. While neutrons can be stable inside an atomic nucleus, free neutrons will decay into a proton, electron and anti-neutrino. Like all radioactive materials, the decay of free neutrons follows the half-life relation, where (on average) half of a collection of neutrons will decay within a given amount of time. One of the basic questions, then, is “what is the half-life of a free neutron?” It turns out there are two ways we can measure neutron half-life, and the results don’t agree.

The first method is known as the beam method. In this method a beam of neutrons is shot into a magnetic “proton trap.” Since the neutrons decay into protons, etc., the number of protons caught by the trap gives you a measure of how many neutrons have decayed in a given time. From this method we get a neutron half-life of between 886 and 890 seconds. The second method is known as the bottle method. This experiment holds ultracold neutrons in a magnetic bottle, and counts the number of neutrons remaining after a period of time. From this we get a neutron half-life of between 878 and 879 seconds. According to our current understanding of physics, these two methods should yield the same result, but they clearly don’t.

We don’t know why that is. One fundamental difference between the methods is that the beam method counts decay products (protons) while the bottle method counts un-decayed neutrons. It is possible that some neutrons decay into something other than a proton, electron and anti-neutrino. Perhaps they decay into some kind of dark matter particle, for example. Another possibility is that cold neutrons held together somehow shorten the half-life slightly due to some yet unknown physics.

While this discrepancy in measurements is vexing on its own, it also has serious implications for astrophysics and cosmology. The amount of hydrogen and helium in the early Universe depended crucially on the number of neutrons and protons available after the big bang. A difference of 15 seconds in neutron half-life would have a measurable impact on the early hydrogen/helium ratio. And if neutrons do, in fact, decay into some kind of dark matter particle, it could solve the mystery of dark matter. But for now all we know is that these two results don’t agree, and we need to figure out why.

Beam method paper: A. T. Yue, et al. Improved Determination of the Neutron Lifetime. Phys. Rev. Lett. 111, 222501 (2013) arXiv:1309.2623 [nucl-ex]

Bottle method paper: A. P. Serebrov, et al. Neutron lifetime measurements using gravitationally trapped ultracold neutrons. Phys. Rev. C 78, 035505 (2008) arXiv:nucl-ex/0702009
Two measurements of the radioactive half-life of free neutrons give results in disagreement with each other, and may point to new physics.
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Thanks Chris, I just received your email regarding science. I looked at it briefly, But I assure you it seems very interesting And will take my time and devour it tonight
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Work
Occupation
Programmer, software architect
Employment
  • Sony Creative Software
    Staff Software Engineer, 2012 - present
  • Avid Technology
    Sr Principal Software Engineer, 2007 - 2012
  • Clotho Advanced Media
    Sr Software Developer, 2001 - 2007
  • Univ Wisconsin, Astronomy Dept
    Research Assistant, 1994 - 2000
Story
Tagline
programmer, cyclist, gamer, former astronomer
Bragging rights
#1 Google result for "constellations"; Toughest bicycle ride: 125 miles + 11,000 ft climbing
Education
  • University of Wisconsin-Madison
    Astronomy, PhD, 1994 - 2000
  • Cornell University
    Astronomy, 1990 - 1994
  • Derryfield School
    1986 - 1990