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Black-body radiation
When astronomers refer to the temperature of a star, they are talking about the temperature of the gases in the photosphere, and they express those temperatures on the Kelvin temperature scale. On this scale, zero degrees Kelvin (written 0 K) is absolute zero (2273.2°C or 2459.7°F), the temperature at which an object contains no thermal energy that can be extracted. Water freezes at 273 K and boils at 373 K (at sea-level atmospheric pressure). The Kelvin temperature scale is useful in astronomy because it is based on absolute zero and consequently is related directly to the motion of the particles in an object.
Now you can understand why a hot object glows, or to put it another way, why a hot object emits photons, bundles of electromagnetic energy. The hotter an object is, the more motion there is among its particles. The agitated particles, including electrons, collide with each other, and when electrons accelerate—change their motion—part of the energy is carried away as electromagnetic radiation. The radiation emitted by a heated object is called black-body radiation, a name translated from a German term that refers to the way a perfectly opaque object would behave. A perfectly opaque object would be both a perfectly efficient absorber and a perfectly efficient emitter of radiation. At room temperature, such a perfect absorber and emitter would look black, but at higher temperatures it would glow at wavelengths visible to a human eye. That explains why in astronomy and physics contexts you will see the term black-body referring to objects that glow brightly.
Black-body radiation is quite common. In fact, it is responsible for the light emitted by an incandescent light bulb. Electricity flowing through the filament of the bulb heats it to high temperature, and it glows. You can also recognize the light emitted by hot lava as black-body radiation. Many objects in the sky, including the sun and other stars, primarily emit black-body radiation because they are mostly opaque.
Credit: Michael A. Seeds, Dana E. Backman
Gif credit: caucasianmale
(via itsfullofstars)
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“Probably no stars will physically hit each other. There’s just so much space between the stars, but when Andromeda collides with us it’ll have a huge impact on the Milky Way. Some things will get thrown into the black hole in the middle, some stars will get ripped off and thrown away into space, so it’ll be dramatic. And the entire night sky will change.” - The Universe S1E9 Alien Galaxies
(Source: galactic-centre, via n-a-s-a)
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High ResolutionHow the Mighty Winds of Uranus and Neptune Blow
The powerful winds of Uranus and Neptune are apparently confined to tight layers in both planets, researchers have determined.
These findings could shed light on how those immensely strong winds are born, and how giant planets form and evolve over time, scientists added.
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![matthen:
When you plot the position of Mars in the sky, you’ll notice that in general it moves from West to East. But when we are closest to Mars, it seems to go backwards for a bit before continuing. This is called retrograde motion, and this challenged early models of the Solar system which had Earth at the centre. The animation shows why Mars appears to go backwards for a bit. [more] [code]](http://25.media.tumblr.com/tumblr_lld3ozwD5f1qfg7o3o1_400.gif)
When you plot the position of Mars in the sky, you’ll notice that in general it moves from West to East. But when we are closest to Mars, it seems to go backwards for a bit before continuing. This is called retrograde motion, and this challenged early models of the Solar system which had Earth at the centre. The animation shows why Mars appears to go backwards for a bit. [more] [code]
(via we-are-star-stuff)
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High ResolutionDeep, Detailed Image of Distant Universe
Apr. 30, 2013 — Staring at a small patch of sky for more than 50 hours with the ultra-sensitive Karl G. Jansky Very Large Array (VLA), astronomers have for the first time identified discrete sources that account for nearly all the radio waves coming from distant galaxies. They found that about 63 percent of the background radio emission comes from galaxies with gorging black holes at their cores and the remaining 37 percent comes from galaxies that are rapidly forming stars.
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High ResolutionEyeball Earths
Alien worlds resembling giant eyeballs might exist around red dwarf stars, and researchers are now proposing experiments to simulate these distant planets and see how capable they are of supporting life.
Red dwarfs are small, faint stars about one-fifth as massive as the Sun and up to 50 times dimmer. They are the most common stars in the galaxy and make up to 70 percent of the stars in the universe, vast numbers that potentially make them valuable places to look for extraterrestrial life. Indeed, the latest results from NASA’s Kepler space observatory reveal that at least half of these stars host rocky planets that are half to four times the mass of Earth. -
High ResolutionIntroducing Kepler-62: A Star System With Two Earths?
Two Earth-sized planets have been discovered orbiting Kepler-62, a star approximately 1,200 light-years away, inside its habitable zone. Which, quite frankly, is bonkers.
“We’re particularly delighted to find that there are two planets in the habitable zone.” — lead Kepler scientist William Borucki
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High ResolutionAn Earth-Sized Planet is Orbiting the Nearest Star
The triple star system of Alpha Centauri is only 4.3 light-years—about 25 trillion miles—away. The possibility of an earth-like world orbiting our nearest neighbor has been a kind of holy grail of astronomy — and something taken for granted by countless SciFi authors.
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The entire evolution of the moon is a story of catastrophes. Carl Sagan
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Meteorites on Mars
The sky falls on Mars, too, just as it does sometimes on Earth. In its long crosscountry drive over the pool table expanse of Meridiani Planum, Mars Exploration Rover Opportunity has encountered more than a dozen meteorites, all of them iron or stony-iron in composition.
Meteorites found on Mars are curiosities, but they can be something more than that, as a paper in the Journal of Geophysical Research points out. A team of scientists led by James Ashley (Arizona State University) notes that because we have samples on Earth of the same kinds of meteorites found there, scientists can use the weathering seen on the Martian examples to probe bygone Martian climates.
The paper details three of Opportunity’s Mars meteorites, dubbed Block Island, Shelter Island, and Mackinac Island. Block Island was found by Opportunity on sol (Mars day) 1961 (July 31, 2009), Shelter Island on sol 2022 (October 1, 2009), and Mackinac Island on sol 2034 (October 14, 2009).Scientists are naming rocks of scientific interest after islands on earth.
What’s most distinctive about these meteorites is that they show evidence for repeated episodes of weathering. For example, Block Island (an iron meteorite) shows two dramatically different faces: one smoothed, probably by sandblasting, and the other deeply pitted, probably by acidic corrosion. The corrosion likely occurred as thin films of water encountered iron sulfide minerals commonly found in iron meteorites.
Both Block Island and Shelter Island show evidence for multi-stage weathering. Close examination of their surfaces show that both have lost through weathering the fusion crusts that meteorites commonly develop as they speed through the atmosphere. Then exposure to water (or probably ice) created an oxydized (rusted) outer layer. This in turn has been largely scoured away by wind erosion.
There’s no way at present to determine how long those meteorites rested on the surface before Opportunity rolled by. But the weathering is unlikely to have happened recently, given Mars’ current arid, cold climate. Yet scientists know that over the last half million years at least, the planet’s spin axis has changed its tilt with respect to the Martian orbit. This has produced periods when snow and ice have come down from the polar regions and accumulated near the equator, probably including Meridiani Planum.
Credit: NASA/JPL
(via itsfullofstars)
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High ResolutionSIXTY SYMBOLS - short videos explaining the symbols in physics and astronomy.
Learn about the meanings and origins of all those symbols.
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High ResolutionClick to enlarge
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High ResolutionPlanck shows almost perfect cosmos – plus axis of evil
The universe is almost perfect, 80 million years older than we thought, and maybe a little bit evil.
That’s the conclusion of a four-year mission conducted by the European Space Agency’s Planck spacecraft, which has created the highest-resolution map yet of the entire cosmic microwave background (CMB) – the first light to travel across a newly transparent universe about 380,000 years after the big bang.
I love how everytime we get new data on the age of the universe (or the earth) it turns out to be even older.
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If you were to move all of the matter in the universe into one corner, how much space would it take up?
It’s hard to answer this question exactly because there are some unknowns. But if you are willing to accept three assumptions, we can come up with an answer that sounds reasonable.
The first question is, “How big is the universe?” No one knows, but this Question of the Day assumes that the universe is a cube that is 30 billion light years on each side. That means that the whole universe contains about 2.7E+31 cubic light years.
The next question is, “How much matter does the universe contain?” The mass of the universe is a source of debate right now because there is no easy way to put the universe on a scale. This NASA page and this “Extension, Age and Mass of the Universe” article discuss different techniques that scientists use to estimate the mass. The latter article also includes an estimate of about 1.6E+60 kilograms for the mass of the universe. Other estimates give other numbers, but all are in that ballpark.
The next question is, “What density do you want to assume the mass will have once you push all of it into one corner?” Now, if you were really to do this - if you actually did move all of the mass of the universe into one corner - it would condense instantly into a black hole and potentially ignite another big bang. But let’s say that you could keep it from doing that, and you were somehow able to keep all of the mass evenly distributed at the density of the sun. According to “Magnitudes of Physics”, the density of the sun is about 1,410 kilograms per cubic meter. (For comparison, the density of water is 1,000 kilograms per cubic meter.)
If you are willing to accept these three assumptions, then:
1.1E+57 cubic meters of matter in the universe
A cubic light year contains about 1E+48 cubic meters. So all of the matter in the universe would fit into about 1 billion cubic light years, or a cube that’s approximately 1,000 light years on each side. That means that only about 0.0000000000000000000042 percent of the universe contains any matter. The universe is a pretty empty place!
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High ResolutionThis illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth’s night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull.
Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger
Source: NASA’s Hubble Shows Milky Way is Destined for Head-On Collision (Hubble Space Telescope site)
What an amazing frame of reference.
Divine Irony
is a rich archive of religious delusions, scientific truths and political implications.
"Tell people there’s an invisible man in the sky who created the universe, and the vast majority believe you. Tell them the paint is wet, and they have to touch it to be sure."
-George Carlin
“If people are good only because they fear punishment, and hope for reward, then we are a sorry lot indeed”.
-Albert Einstein
