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Roger
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A T Tauri star looks like a red or orange star. Their surface temperature is a bit cooler than the Sun’s, but they are brighter than a typical main-sequence star of the same type. The reason for this is that they have not finished collapsing, so they are larger than a similar mass star. Their heat is not generated by fusion in their core, but rather from their gravitational collapse. They also produce a great deal of stellar wind.

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Meet The Newest Classification For Planets: The Gas Dwarf

We just got a new kind of planet! Learn about these worlds at:
http://bit.ly/1oX2cXv

Image via NASA
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Comet PanSTARRS with Galaxy
Image Credit & Copyright: Alessandro Falesiedi
http://apod.nasa.gov/apod/ap140606.html

Sweeping slowly through northern skies, the comet PanSTARRS C/2012 K1 posed for this telescopic portrait on June 2nd in the constellation Ursa Major. Now in the inner solar system, the icy body from the Oort cloud sports two tails, a lighter broad dust tail and crooked ion tail extending below and right. The comet's condensed greenish coma makes a nice contrast with the spiky yellowish background star above. NGC 3319 appears at the upper left of the frame that spans almost twice the apparent diameter of the full Moon. The spiral galaxy is about 47 million light-years away, far beyond the stars in our own Milky Way. In comparison, the comet was a mere 14 light-minutes from our fair planet. This comet PanSTARRS will slowly grow brighter in the coming months remaining a good target for telescopic comet watchers and reaching perihelion, its closest approach to the Sun, while just beyond Earth's orbit in late August.
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Venus and Earth are very similar, but Venus is a dry planet while Earth is wet.  Why is that? Several models have been proposed, but it might be as simple as their distance from the Sun.

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Testing Metal

In astronomy, all elements other than hydrogen and helium are referred to as “metals.” For this reason, a measure of the amount of other elements a star contains is known as its metallicity. One way to define the metallicity of a star is simply as the fraction of a star’s mass which is not hydrogen or helium. For the Sun, this number is Z = 0.02, which means that about 2% of the Sun’s mass is “metal”. Another way to express the metallicity of a star is by its ratio of Iron to Hydrogen, known as [Fe/H]. This is given on a logarithmic scale relative to the ratio of our Sun. So the [Fe/H] of our Sun is zero. Stars with lower metallicity will have negative [Fe/H] values, and ones with higher metallicity have positive values.When it comes to planetary systems, it’s generally been thought that planets would tend to form around stars with a higher metallicity. At a broad level that makes sense because rocky planets such as Earth can only form in a system where there are enough metals like iron, silicon, carbon and the like.  You can’t make a terrestrial planet out of just hydrogen and helium.  But now that we’ve discovered lots of exoplanetary systems, we can actually put this idea to the test. A recent paper in Nature has done just that, and they’ve found something rather interesting.

In the paper, the authors looked at about 400 stars with exoplanets (about 600 exoplanets in all).  They then compared the size of the exoplanets with the metallicity of their stars.  What they found was that there was a distinct relation between the metallicity of a star and the type of planets it has.  Stars with a metallicity similar to our Sun’s were more likely to have terrestrial planets, while stars with higher metallicity tend to have gas dwarfs, or gas giants (Jupiter-like).  The study also showed that high metallicity stars are likely to have so-called “hot-Jupiters”. That is, large gas giants orbiting close to a star.

We’ve seen in computer models how large protoplanets will tend to migrate inward toward the star as they form. This new work would seem to support that idea, since higher metallicity stars would be more likely to form gas giants early on, thus allowing them to migrate inward to become hot Jupiters.

So it seems that metallicity is a significant factor in planetary formation, and higher metallicity stars will tend to form larger planets.  But it also seems that stars similar to the Sun are better suited for having terrestrial planets like ours.

Image: From the paper.

Paper: Lars A. Buchhave, et al. Three regimes of extrasolar planet radius inferred from host star metallicities. Nature 509, 593–595 (2014)
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So this is potentially useful - a colour generator Sure, at first i was like why is this getting so much attention, but then I saw its implementation is quite elegant - you can ask it for random colours of a given hue for example (as illustrated below) http://llllll.li/randomColor/
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One Does Not Simply Telnet into Mordor...but they can ssh ;-)  #linux
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Astronomers Confounded By Massive Rocky World - Astronomers have discovered a rocky planet that weighs 17 times as much as Earth and is more than twice as large in size. This discovery has planet formation theorists challenged to explain how such a world could have formed. Worlds such as this were not thought possible to exist. More: http://go.nasa.gov/1n5z2SF 

This image is an artist concept. Credit: Harvard-Smithsonian Center for Astrophysics/David Aguilar

#planets #nasa #kepler #astronomy #science #exoplanet #earth
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The universe is billions of years old, and we humans have only been observing it for a tiny fraction of all that time.  How is it, then that we can know things like the age of stars, how they form and die?  It would be like an alien race learning about humanity by observing us for only a fraction of a second.

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One of the ways in which astronomy and astrophysics differ is that astronomy is concerned with observed phenomena, and astrophysics is concerned with the mechanism behind the phenomena.  This means that sometimes we discover radically different phenomena have a common cause.
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