One of our Sun’s unusual features is its orbit around the center of the galaxy, which is significantly less elliptical (“eccentric”) than those of other stars similar in age (and therefore metallicity, or proportion of an object’s chemical composition other than hydrogen and helium) and type and is barely inclined relative to the Galactic plane. This circularity in the Sun’s orbit prevents it from plunging into the inner Galaxy where life-threatening supernovae are more common. Moreover, the small inclination to the galactic plane avoids abrupt crossings of the plane that would stir up the Sun’s Oort Cloud and bombard the Earth with life-threatening comets.
In fact, the Sun is orbiting very close to the “co-rotation radius” of the galaxy, where the angular speed of the galaxy’s spiral arms matches that of the stars within. As a result, the Sun avoids crossing the spiral arms very often, which would expose Earth to supernovae that are more common there. These exceptional circumstances may have made it more likely for complex life and human intelligence to emerge on Earth. According to Guillermo Gonzalez (an astronomer at Iowa State University), fewer than five percent of all stars in the galaxy enjoy such a life-enhancing galactic orbit. Other astronomers point out, however, that many nearby stars move with the Sun in a similar galactic orbit.
The Sun resides in a pancake region of the Galaxy called the “disk” with a strong concentration of stars (and gas and dust) within 3,000 light-years (ly) of the galactic plane, which includes the so-called “thin disk” that has more relatively younger stars within 1,500 ly of the plane (more on stellar population groups in our Milky Way Galaxy). This region contains relatively young to intermediate-aged stars that within around five billion years old with relatively higher average metallicity than other galactic regions located outside of the galactic core, in a circular band that broadens with time. Generated by the deaths of older stars, the greater availability of elements higher than hydrogen and helium in this galactic region favor the formation of rocky inner planets as large as Earth, or bigger (Gonzalez et al, 2001). Moreover, the galactic orbits of stars in this region tend to be relatively circular — with low to moderate eccentricity. According to one recent definition of the galactic habitable zone, as much as 10 percent of all stars in the Milky Way may have experienced chemical and environmental conditions suitable for the development of complex Earth-type life over the past eight to four billion years for evolutionary development (press release; and Lineweaver et al, 2004, in pdf). (Further discussion of the different galactic regions and their distinctive stellar populations is available from ChView’s “The Stars of the Milky Way.”)
In recent millenia, the Sun has been passing through a Local Interstellar Cloud (LIC) that is flowing away from the Scorpius-Centaurus Association of young stars dominated by extremely hot and bright O and B spectral types, many of which will end their brief lives violently as supernovae. The LIC is itself surrounded by a larger, lower density cavity in the interstellar medium (ISM) called the Local Bubble, that was probably formed by one or more relatively recent supernova explosions. As shown in a 2002 Astronomy Picture of the Day, located just outside the Local Bubble are: high-density molecular clouds such as the Aquila Rift which surrounds some star forming regions; the Gum Nebula, a region of hot ionized hydrogen gas which includes the Vela Supernova Remnant, which is expanding to create fragmented shells of material like the LIC; and the Orion Shell and Orion Association, which includes the Great Orion Nebula, the Trapezium of hot B- and O-type stars, the three belt stars of Orion, and local blue supergiant star Rigel.
It’s never really dark
The very weak emission of light by a planetary atmosphere. In the case of Earth’s atmosphere, this optical phenomenon causes the night sky to never be completely dark (even after the effects of starlight and diffused sunlight from the far side are removed). [*]
Now that he’s got your attention with his spectacular photos, geoscientist Kristian Klepp would like to teach you something. At least that’s the general idea behind his very cool website www.lichtjahre.eu.
About the site:
The aim is to increase public awareness of the earth system, so that people can develop a clearer understanding of the planet. Over 200 images of spectacular landscapes accompanied by scientific explanations illustrate the perpetual change of our planet through the eons of time.
MILKY WAY’S GAMMA RAY BUBBLES SHAPED BY DARK MATTER?
Dark matter, the elusive stuff that makes up a substantial portion of all the mass in the universe, is largely a mystery to astronomers. They’ve tried finding it and creating it, but so far no conclusive proof as to what exactly it is though most theories state that we interact with it through gravity.
But Christoph Weniger, of the Max Planck Institute for Physics in Munich, has a different theory to explain new possible evidence for dark matter. By carrying out statistical analysis of three and a half years worth of publicly available data from NASA’s Fermi Space Telescope, he’s found a gamma ray line across the sky that he says is a clear signature of dark matter.
Photoset reblogged from with 3,717 notes
For #Starporn Saturday.
We should totally make that a thing.
Source: Daily Mail
What color is the Milky Way?
Our galaxy looks white, the color of fresh spring snow in the early morning, but unfortunately, because we are located well within our galaxy, clouds of gas and dust obscure all but the closest regions of the galaxy from view, keeping us from directly seeing what color our galaxy is as a whole. But scientists are looking at galaxies similar to the Milky Way to determine trends in colorization.
New ‘Event-Horizon Telescope’ to Zoom in for 1st Ever Photo of Milky Way’s Supermassive Black Hole
“In essence, we are making a virtual telescope with a mirror that is as big as the Earth.”
Sheperd Doeleman, Massachusetts Institute of Technology (MIT)
“On Wednesday, Jan. 18, astronomers, physicists and scientists from related fields will convene in Tucson, Ariz. from across the world to discuss an endeavor that only a few years ago would have been regarded as nothing less than impossible. The conference is organized by Dimitrios Psaltis, an associate professor of astrophysics at the University of Arizona’s Steward Observatory, and Daniel Marrone, an assistant professor of astronomy at Steward Observatory.
“Nobody has ever taken a picture of a black hole,” Psaltis said. “We are going to do just that.”“Even five years ago, such a proposal would not have seemed credible,” added Sheperd Doeleman, assistant director of the Haystack Observatory at Massachusetts Institute of Technology (MIT), who is the principal investigator of the Event Horizon Telescope, as the project is dubbed.
“Now we have the technological means to take a stab at it.”First postulated by Albert Einstein’s Theory of General Relativity, the existence of black holes has since been supported by decades’ worth of observations, measurements and experiments. But never has it been possible to directly observe and image one of these maelstroms whose sheer gravity exerts such cataclysmic power they twist and mangle the very fabric of space and time.
“Black holes are the most extreme environment you can find in the universe,” Doeleman said.The field of gravity around a black hole is so immense that it swallows everything in its reach; not even light can escape its grip. For that reason, black holes are just that –emitting no light whatsoever, their “nothingness” blends into the black void of the universe.So how does one take a picture of something that by definition is impossible to see?”As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues,” Doeleman explained.”
http:// www.dailygalaxy.com/ my_weblog/2012/01/ new-event-horizon-telescope -to-zoom-in-for-1st-ever-p hoto-of-milky-ways-superma ssive-black-hole.htmlSource:Milky way scientists
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