Sunday, December 13, 2015

How Does The Sun Produce Energy?

How Does The Sun Produce Energy?:



The Sun provides energy for life here on Earth through light and heat. Credit: NASA Goddard Space Flight Center


There is a reason life that Earth is the only place in the Solar System where life is known to be able to live and thrive. Granted, scientists believe that there may be microbial or even aquatic life forms living beneath the icy surfaces of Europa and Enceladus, or in the methane lakes on Titan. But for the time being, Earth remains the only place that we know of that has all the right conditions for life to exist.

One of the reasons for this is because the Earth lies within our Sun's Habitable Zone (aka. "Goldilocks Zone"). This means that it is in right spot (neither too close nor too far) to receive the Sun's abundant energy, which includes the light and heat that is essential for chemical reactions. But how exactly does our Sun go about producing this energy? What steps are involved, and how does it get to us here on planet Earth?



The simple answer is that the Sun, like all stars, is able to create energy because it is essentially a massive fusion reaction. Scientists believe that this began when a huge cloud of gas and particles (i.e. a nebula) collapsed under the force of its own gravity - which is known as Nebula Theory. This not only created the big ball of light at the center of our Solar System, it also triggered a process whereby hydrogen, collected in the center, began fusing to create solar energy.

Technically known as nuclear fusion, this process releases an incredible amount of energy in the form of light and heat. But getting that energy from the center of our Sun all the way out to planet Earth and beyond involves a couple of crucial steps. In the end, it all comes down to the Sun's layers, and the role each of them plays in making sure that solar energy gets to where it can help create and sustain life.

https://youtu.be/y6g7c00v_nY

The Core:
The core of the Sun is the region that extends from the center to about 20–25% of the solar radius. It is here, in the core, where energy is produced by hydrogen atoms (H) being converted into molecules of helium (He). This is possible thanks to the extreme pressure and temperature that exists within the core, which are estimated to be the equivalent of 250 billion atmospheres (25.33 trillion KPa) and 15.7 million kelvin, respectively.

The net result is the fusion of four protons (hydrogen molecules) into one alpha particle - two protons and two neutrons bound together into a particle that is identical to a helium nucleus. Two positrons are released from this process, as well as two neutrinos (which changes two of the protons into neutrons), and energy.

The core is the only part of the Sun that produces an appreciable amount of heat through fusion. In fact, 99% of the energy produced by the Sun takes place within 24% of the Sun's radius. By 30% of the radius, fusion has stopped almost entirely. The rest of the Sun is heated by the energy that is transferred from the core through the successive layers, eventually reaching the solar photosphere and escaping into space as sunlight or the kinetic energy of particles.

The Sun releases energy at a mass–energy conversion rate of 4.26 million metric tons per second, which produces the equivalent of 38,460 septillion watts (3.846×1026 W) per second. To put that in perspective, this is the equivalent of about 9.192×1010 megatons of TNT per second, or 1,820,000,000 Tsar Bombas - the most powerful thermonuclear bomb ever built!



Radiative Zone:
This is the zone immediately next to the core, which extends out to about 0.7 solar radii. There is no thermal convection in this layer, but solar material in this layer is hot and dense enough that thermal radiation is all that is needed to transfer the intense heat generated in the core outward. Basically, this involves ions of hydrogen and helium emitting photons that travel a short distance before being reabsorbed by other ions.

Temperatures drop in this layer, going from approximately 7 million kelvin closer to the core to 2 million at the boundary with the convective zone. Density also drops in this layer a hundredfold from 0.25 solar radii to the top of the radiative zone, going from 20 g/cm³ closest to the core to just 0.2 g/cm³ at the upper boundary.

Convective Zone:
This is the Sun's outer layer, which accounts for everything beyond 70% of the inner solar radius (or from the surface to approx. 200,000 km below). Here, the temperature is lower than in the radiative zone and heavier atoms are not fully ionized. As a result, radiative heat transport is less effective, and the density of the plasma is low enough to allow convective currents to develop.

Because of this, rising thermal cells carry the majority of the heat outward to the Sun's photosphere. Once these cells rise to just below the photospheric surface, their material cools, causing their density increases. This forces them to sink to the base of the convection zone again - where they pick up more heat and the convective cycle continues.



At the surface of the Sun, the temperature drops to about 5,700 K. The turbulent convection of this layer of the Sun is also what causes an effect that produces magnetic north and south poles all over the surface of the Sun.

It is also on this layer that sunspots occur, which appear as dark patches compared to the surrounding region. These spots correspond to concentrations in the magnetic flux field that inhibit convection and cause regions on the surface to drop in temperature to compared to the surrounding material.

Photosphere:
Lastly, there is the photosphere, the visible surface of the Sun. It is here that the sunlight and heat that are radiated and convected to the surface propagate out into space. Temperatures in the layer range between 4,500 and 6,000 K (4,230 - 5,730 °C; 7646 - 10346 °F). Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening.

The photosphere is tens to hundreds of kilometers thick, and is also the region of the Sun where it becomes opaque to visible light. The reasons for this is because of the decreasing amount of negatively charged Hydrogen ions (H-), which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H- ions.

The energy emitted from the photosphere then propagates through space and reaches Earth's atmosphere and the other planets of the Solar System.  Here on Earth, the upper layer of the atmosphere (the ozone layer) filters much of the Sun's ultra-violet (UV) radiation, but passes some onto the surface. The energy that received is then absorbed by the Earth's air and crust, heating our planet and providing organisms with a source of energy.



The Sun is at the center of biological and chemical processes here on Earth. Without it, the life cycle of plants and animals would end, the circadian rhythms of all terrestrial creatures would be disrupted; and in time, all life on Earth would cease to exist. The Sun's importance has been recognized since prehistoric times, with many cultures viewing it as a deity (more often than not, as the chief deity in their pantheons).

But it is only in the past few centuries that the processes that power the Sun have come to be understood. Thanks to ongoing research by physicists, astronomers and biologists, we are now able to grasp how the Sun goes about producing energy, and how it passes that on to our Solar System. The study of the known universe, with its diversity of star systems and exoplanets - has also helped us to draw comparisons with other types of stars.

We have written many articles about the Sun and Solar Energy for Universe Today. Here is What Color is the Sun?, How Far is Earth from the Sun?, some Interesting Facts About the Sun, and one about the Characteristic of the Sun.

For those who are interesting in the truly speculative and futuristic, here's Could We Terraform The Sun?, and Harvesting Solar Power from Space.

For more information, check out NASA's Solar System Exploration Guide on the Sun, and here's a link to the SOHO mission homepage, which has the latest images from the Sun.

Astronomy Cast also has some interesting episodes about the Sun. Listen here, Episode 30: The Sun, Spots and All, and Episode 320: Layers of the Sun.


Posted by Nelio Inacio at 12:54 PM 0 comments

Dawn Spacecraft Unraveling Mysteries of Ceres Intriguing Bright Spots as Sublimating Salt Water Residues

Dawn Spacecraft Unraveling Mysteries of Ceres Intriguing Bright Spots as Sublimating Salt Water Residues:



This representation of Ceres' Occator Crater in false colors shows differences in the surface composition. Occator measures about 60 miles (90 kilometers) wide. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA


With NASA’s Dawn spacecraft set to enter its final and lowest orbit around the dwarf planet Ceres, spectral measurements are enabling researchers to gradually unravel the nature of the numerous mysterious and intriguing bright spots recently discovered and now conclude that briny mixtures of ice and salts apparently reside just beneath certain patches of the pockmarked surface and that “water is sublimating” from the surface of an “active crater”.

Indeed, excited scientists report that high resolution images and spectra from Dawn indicate that Ceres is an active world even today, according to a pair of newly published scientific papers in the journal Nature.

Ceres occupies a very ”unique niche” unlike any other world in our Solar System with “occasional water leakage on to the surface,” Dawn Principal Investigator Chris Russell told Universe Today.

Orbital measurements from the probes Framing camera reveal that the bright areas likely contain hydrated magnesium sulphates, a class of mineral salts found inside the brightest spot on Ceres, namely Occator crater - which are the salt-rich leftover residues from water evaporation.

The newly released results also show evidence of a diffuse haze of water vapor above Occator crater, which appears to be among the youngest features on Ceres, as well as at a second region at Oxo crater.

The Cerean haze is formed by the warming effects of sunlight shining on the hydrated salts inside the crater. The salts were exposed by past impacts of asteroids all across Ceres. The haze could be comprised of “condensed-ice or dust particles.”

“The Occator crater on the surface of dwarf planet Ceres is active: data from NASA’s Dawn mission indicate water sublimating from its center,” say Dawn researchers in a statement.

https://youtu.be/8er_0yY1S1o

Video caption: Ceres Rotation and Occator Crater. Dwarf planet Ceres is shown in these false-color renderings, which highlight differences in surface materials. Images from NASA’s Dawn spacecraft were used to create a movie of Ceres rotating, followed by a flyover view of Occator Crater, home of Ceres’ brightest area. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA


“Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles9, 10 may explain this haze,” write the authors in the Nature paper.

Occator is the brightest of more than 130 strikingly bright patches spread across the Texas-sized world, which ranks as the largest object in the main asteroid belt between Mars and Jupiter. It has an average diameter is 584 miles (940 kilometers).



NASA says Occator is a rather new impact crater, formed by an asteroid impact as recently as only 70 million years.

“The most plausible interpretation of our results is that there is a mixture of ice and salts under at least some parts of Ceres’ surface,” says lead study author Andreas Nathues of the Max Planck Institute for Solar System Research, Göttingen, Germany, in a statement.

“This material could be exposed by the impacts of medium-sized asteroids. The ice gradually evaporates until only salts and phyllosilicates are left.”

The mysterious bright spots inside Occator crater - looking somewhat like a pair of alien eyes - were only discovered earlier this year as NASA’s Dawn orbiter was on its final approach to Ceres.

Occator measures about 60 miles (90 kilometers) across and 2 miles (4 kilometers) deep. It also features a central pit “covered by this bright material, that measures about 6 miles (10 kilometers) wide and 0.3 miles (0.5 kilometers) deep. Dark streaks, possibly fractures, traverse the pit. Remnants of a central peak, which was up to 0.3 miles (0.5 kilometers) high, can also be seen,” say officials.



Prior to entering orbit on March 6, 2015, scientists speculated that Ceres might harbor a subsurface ocean of liquid water that could be hospitable to life.

Now with new data in hand, the presence of a large subsurface ocean of liquid water or water ice appears ever more likely.

"The global nature of Ceres' bright spots suggests that this world has a subsurface layer that contains briny water-ice," noted Nathues, who is also lead investigator of the Framing camera team.

The bright spots of Occator have captivated popular imaginations worldwide even as scientists struggled mightily, until recently, to explain what they really are.

Possible explanations ranging from frozen ices, salts and cryovolcanoes have been proposed for the past year as researchers sought to gather measurements explaining their elusive cause.

“We are currently probably seeing remnants of an evaporation process exhibiting different stages in different locations. Perhaps we are witnessing the last phase of a formerly more active period”, says Nathues.

To date, there has been no unambiguous detection of water ice on the surface of Ceres.
“Occasional water leakage on to the surface could leave salt there as the water would sublime,” Prof. Chris Russell, Dawn principal investigator told Universe Today recently in an exclusive.

“The big picture that is emerging is that Ceres fills a unique niche.”

“Ceres fills a unique niche between the cold icy bodies of the outer solar system, with their rock hard icy surfaces, and the water planets Mars and Earth that can support ice and water on their surfaces,” Russell, of the University of California, Los Angeles, told me.

On Oct. 23, Dawn began a seven-week-long dive that uses ion thruster #2 to reduce the spacecrafts vantage point from 915 miles (1,470 kilometers) at the High Altitude Mapping Orbit (HAMO) down to less than 235 miles (380 kilometers) above Ceres at the Low Altitude Mapping Orbit (LAMO).

Dawn is slated to arrive at LAMO by mid-December, just in time to begin delivering long awaited Christmas treats.

Dawn is Earth’s first probe in human history to explore any dwarf planet, the first to explore Ceres up close and the first to orbit two celestial bodies.

The asteroid Vesta was Dawn’s first orbital target where it conducted extensive observations of the bizarre world for over a year in 2011 and 2012.

The mission is expected to last until at least March 2016, and possibly longer, depending upon fuel reserves.

“It will end some time between March and December,” Dr. Marc Rayman, Dawn's chief engineer and mission director based at NASA's Jet Propulsion Laboratory, Pasadena, California, told Universe Today.

Stay tuned here for Ken's continuing Earth and planetary science and human spaceflight news.

Ken Kremer


Posted by Nelio Inacio at 12:52 PM 0 comments

10 Interesting Facts About Neptune

10 Interesting Facts About Neptune:



Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL


Neptune is a truly fascinating world. But as it is, there is much that people don't know about it. Perhaps it is because Neptune is the most distant planet from our Sun, or because so few exploratory missions have ventured that far out into our Solar System. But regardless of the reason, Neptune is a gas (and ice) giant that is full of wonder!

Below, we have compiled a list of 10 interesting facts about this planet. Some of them, you might already know. But others are sure to surprise and maybe even astound you. Enjoy!

1. Neptune is the most distant planet:
This may sound like a pretty simple statement, but it's actually rather complicated. When it was first discovered by in 1846, Neptune became the most distant planet in the Solar System. But then in 1930, Pluto was discovered, and Neptune became the second-most distant planet. But Pluto's orbit is very elliptical; and so there are periods when Pluto actually orbits closer to the Sun than Neptune. The last time this happened was in 1979, which lasted until 1999. During that period, Neptune was again the most distant planet.

Then, at the XXVIth General Assembly of the International Astronomical Union - which took place between Aug 14th and 25th, 2006, in Prague - the issue of which was the most distant planet was visited once again. Confronted with the discovery of many Pluto-sized bodies in the Kuiper Belt - i.e. Eris, Haumea, Sedna and Makemake - and the ongoing case of Ceres, the IAU decided it was time to work out a clear definition of what a planet was.

https://youtu.be/BKoRt-6pjAE

In what would prove to be a very controversial decision, the IAU's passed a resolution which defined a planet as “a celestial body orbiting a star that is massive enough to be rounded by its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium.”

As a result of this, Pluto was "demoted" from the status of planet and thereafter defined as a "dwarf planet" instead. And so, Neptune has once again become the most distant planet. At least for now...

2. Neptune is the smallest of the gas giants:
With an equatorial radius of only 24,764 km, Neptune is smaller than all the other gas giants in the Solar System: Jupiter, Saturn and Uranus. But here's the funny thing: Neptune is actually more massive than Uranus by about 18%. Since it's smaller but more massive, Neptune has  a much higher  density than Uranus. In fact, at 1.638 g/cm3, Neptune is the densest gas giant in the Solar System.

3. Neptune's surface gravity is almost Earth-like:
Neptune is a ball of gas and ice, probably with a rocky core. There's no way you could actually stand on the surface of Neptune without just sinking in. However, if you could stand on the surface of Neptune, you would notice something amazing. The force of gravity pulling you down is almost exactly the same as the force of gravity you feel walking here on Earth.

https://youtu.be/htr9lH1PEUU

The gravity of Neptune is only 17% stronger than Earth gravity. That's actually the closest to Earth gravity (one g) in the Solar System. Neptune has 17 times the mass of Earth, but also has almost 4 times larger. This means its greater mass is spread out over a larger volume, and down at the surface, the pull of gravity would be almost identical. Except for the part where you wouldn't stop sinking!

4. The discovery of Neptune is still a controversy:
The first person to have seen Neptune was likely Galileo, who marked it as a star in one of his drawings. However, since he did not identify it as a planet, he is not credited with the discovery. That credit goes to French mathematician Urbain Le Verrier and the English mathematician John Couch Adams, both of whom predicted that a new planet - known as Planet X - would be discovered in a specific region of the sky.

When astronomer Johann Gottfried Galle actually found the planet in 1846, both mathematicians took credit for the discovery. English and French astronomers battled over who made the discovery first, and there are still defenders of each claim to this day. Today, the consensus among astronomers is that Le Verrier and Adams deserve equal credit for the discovery.

5. Neptune has the strongest winds in the Solar System:
Think a hurricane is scary? Imagine a hurricane with winds that go up to 2,100 km/hour. As you can probably imagine, scientists are puzzled how an icy cold planet like Neptune can get its cloud tops t0 move so fast. One idea is that the cold temperatures and the flow of fluid gasses in the planet's atmosphere might reduce friction to the point that it's easy to generate winds that move so quickly.

https://youtu.be/43-xLP-1a7M

6. Neptune is the coldest planet in the Solar System:
At the top of its clouds, temperatures on Neptune can dip down to 51.7 Kelvin, or -221.45 degrees Celsius (-366.6 °F). That's over twice the freezing point of water, which means that an unprotected human being would flash freeze in a second! Pluto gets colder, experiencing temperatures as low as 33 K (?240 °C/-400 °F). But then again, Pluto isn't a planet any more (remember?)

7. Neptune has rings:
When people think of ring systems, Saturn is usually the planet that comes to mind. But would it surprise you to know that Neptune has a ring system as well? Unfortunately, it is rather difficult to observe compared to Saturn's bright, bold ring; which is why it is not so well-recognized. In total, Neptune has five rings, all of which are named after astronomers who made important discoveries about Neptune - Galle, Le Verrier, Lassell, Arago, and Adams.

These rings are composed of at least 20% dust (with some containing as much as 70%) which are micrometer-sized, similar to the particles that make up the rings of Jupiter. The rest of the ring materials consists of small rocks. The planet’s rings are difficult to see because they are dark, which is likely due to the presence of organic compounds that have been altered due to exposition to cosmic radiation. This is similar to the rings of Uranus, but very different than the icy rings around Saturn.

It’s believed that the rings of Neptune are relatively young – much younger than the age of the Solar System, and much younger than the age of Uranus’ rings. Consistent with the theory that Triton was a Kuiper Belt Object (KBO) that was seized by Neptune’s gravity (see below), they are believed to be the result of a collision between some of the planet’s original moons.

https://youtu.be/4R4usDbSLzk

 

8. Neptune probably captured its largest moon, Triton:
Neptune's largest Moon, Triton, circles Neptune in a retrograde orbit. That's means that it orbits the planet backwards relative to Neptune's other moons. This is seen as an indication that Neptune probably captured Triton - i.e. the moon didn't form in place like the rest of Neptune's moons. Triton is locked into a synchronous rotation with Neptune, and is slowly spiraling inward towards the planet.

At some point, billions of years from now, Triton will likely will be torn apart by Neptune's gravitational forces and become a magnificent ring around the planet. This ring will be pulled inward and crash into the planet. It is too bad that such an event will be happening so very long from now, because it would be amazing to watch!

9. Neptune has only been visited once up close:
The only spacecraft that has ever visited Neptune was NASA's Voyager 2 spacecraft, which visited the planet during its Grand Tour of the Solar System. Voyager 2 made its Neptune flyby on August 25, 1989, passing within 3,000 km of the planet's north pole. This was the closest approach to any object that Voyager 2 made since it was launched from Earth.

During its flyby, Voyager 2 studied Neptune's atmosphere, its rings, magnetosphere, and also conduct a close flyby of Triton. Voyager 2 also viewed Neptune's "Great Dark Spot", the rotating storm system which has since disappeared, according to observations by the Hubble Space Telescope. Originally thought to be a large cloud itself, the information gathered by Voyager helped to shed light on the true nature of this phenomenon.

https://youtu.be/COI5LBpvDyU

10. There are no plans to visit Neptune again:
Voyager 2's amazing photographs of Neptune might be all we get for decades, as there are no firm plans to return to the Neptune system.  However, a possible Flagship Mission has been envisioned by NASA to take place sometime during the late 2020s or early 2030s. For example, in 2003, NASA announced tentative plans to send a new Cassini-Huygens-style mission to Neptune, called the Neptune Orbiter.

Also described as a "Neptune Orbiter with Probes", this spacecraft had a proposed launch date of 2016, and would arriving around Neptune by 2030. The proposed mission would go into orbit around the planet and study its weather, magnetosphere, ring system and moons. However, no information on this project has been forthcoming in recent years and it appears to have been scrapped.

Another, more recent proposal by NASA was for Argo - a flyby spacecraft that would be launched in 2019, which would visit Jupiter, Saturn, Neptune, and a Kuiper belt object. The focus would be on Neptune and its largest moon Triton, which would be investigated around 2029.

And these are just of the things that make Neptune such a fascinating planet, and one that is worthy of study. One can only hope that future missions will be launched to the outer Solar System that will be able to dig deeper into its many mysteries.

We have many interesting articles about Neptune here at Universe Today. Here is one about the Rings of Neptune, the Moons of Neptune, Who Discovered Neptune?, and Are There Oceans on Neptune?

If you'd like more information on Neptune, take a look at Hubblesite's News Releases about Neptune, and here's a link to NASA's Solar System Exploration Guide to Neptune.

Astronomy Cast has some interesting episodes about Neptune. You can listen here, Episode 63: Neptune and Episode 199: The Voyager Program.


Posted by Nelio Inacio at 12:51 PM 0 comments

Friday, December 11, 2015

Cygnus: Bubble and Crescent

Cygnus: Bubble and Crescent: APOD: 2015 December 4 - Cygnus: Bubble and Crescent



Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.


2015 December 4


See Explanation. Clicking on the picture will download the highest resolution version available.



Cygnus: Bubble and Crescent
Image Credit & Copyright: Ivan Eder
Explanation: These clouds of gas and dust drift through rich star fields along the plane of our Milky Way Galaxy toward the high flying constellation Cygnus. Caught within the telescopic field of view are the Soap Bubble (lower left) and the Crescent Nebula (upper right). Both were formed at a final phase in the life of a star. Also known as NGC 6888, the Crescent was shaped as its bright, central massive Wolf-Rayet star, WR 136, shed its outer envelope in a strong stellar wind. Burning through fuel at a prodigious rate, WR 136 is near the end of a short life that should finish in a spectacular supernova explosion. recently discovered Soap Bubble Nebula is likely a planetary nebula, the final shroud of a lower mass, long-lived, sun-like star destined to become a slowly cooling white dwarf. While both are some 5,000 light-years or so distant, the larger Crescent Nebula is around 25 light-years across.

Tomorrow's picture: exo-orrery
< | Archive | Submissions | Search | Calendar | RSS | Education | About APOD | Discuss | >
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
NASA Web Privacy Policy and Important Notices
A service of: ASD at NASA / GSFC
& Michigan Tech. U.


Posted by Nelio Inacio at 7:11 AM 0 comments

Comet Catalina Emerges

Comet Catalina Emerges:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2015 December 7


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Comet Catalina is ready for its close-up. The giant snowball from the outer Solar System, known formally as C/2013 US10 (Catalina), rounded the Sun last month and is now headed for its closest approach to Earth in January. With the glow of the Moon now also out of the way, morning observers in Earth's northern hemisphere are getting their best ever view of the new comet. And Comet Catalina is not disappointing. Although not as bright as early predictions, the comet is sporting both dust (lower left) and ion (upper right) tails, making it an impressive object for binoculars and long-exposure cameras. The featured image was taken last week from the Canary Islands, off the northwest coast of Africa. Sky enthusiasts around the world will surely be tracking the comet over the next few months to see how it evolves.

Posted by Nelio Inacio at 7:10 AM 0 comments

Arp 87: Merging Galaxies from Hubble

Arp 87: Merging Galaxies from Hubble: APOD: 2015 December 9 - Arp 87: Merging Galaxies from Hubble



Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.


2015 December 9


See Explanation. Clicking on the picture will download the highest resolution version available.



Arp 87: Merging Galaxies from Hubble
Image Credit: NASA, ESA, Hubble Space Telescope; Processing: Douglas Gardner
Explanation: This dance is to the death. Along the way, as these two large galaxies duel, a cosmic bridge of stars, gas, and dust currently stretches over 75,000 light-years and joins them. The bridge itself is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. Together, the system is known as Arp 87 and morphologically classified, technically, as peculiar. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the death of one galaxy in the sense that only one galaxy will eventually result. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 pair are about 300 million light-years distant toward the constellation Leo. The prominent edge-on spiral at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

Tomorrow's picture: series cytherean
< | Archive | Submissions | Index | Search | Calendar | RSS | Education | About APOD | Discuss | >
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
NASA Web Privacy Policy and Important Notices
A service of: ASD at NASA / GSFC
& Michigan Tech. U.


Posted by Nelio Inacio at 7:09 AM 0 comments

Viewing Guide to the 2015 Geminid Meteor Shower

Viewing Guide to the 2015 Geminid Meteor Shower:



A brilliant Geminid meteor shower photographed from Mt. Balang, China. Credit: NASA/Kevin Wu


A brilliant Geminid flashes below Sirius and Orion over Mount Balang in China. Credit: NASA/Alvin Wu
2015 looks like a fantastic year for the Geminids. With the Moon just 3 days past new and setting at the end of evening twilight, conditions couldn’t be more ideal. Provided the weather cooperates! But even there we get a break. With a maximum of 120 meteors per hour, the shower is expected to peak around 18:00 UT (1 p.m. EST, 10 a.m. PST) December 14th, making for two nights of approximately equal activity: Sunday night Dec. 13-14 and Monday night Dec. 14-15.



You can start watching for Geminids early in the evening December 13th. The radiant of the shower lies near the bright pair of stars, Castor and Pollux. Source: Stellarium


You can start watching for Geminids early in the evening both Sunday and Monday nights (Dec. 13-14). The shower radiant lies right next door to the bright stellar duo Castor and Pollux in the constellation Gemini above Orion. Source: Stellarium
That 120 meteor tally would be what you’d see from a dark, moonless sky with the radiant at the zenith. Your count will vary depending on whether you observe from the suburbs or the countryside and what time of night you go out. Closer to 50 per hour from locations near moderate-sized cities might be more realistic. Many meteor showers require getting up in the wee hours of the morning when the radiant has climbed high enough for a good view. Happily, the Geminids are different. The shower radiant already stands some 30° high in the eastern sky at 10 o’clock local time, making for a good hour of meteor-watching before you hit the hay Sunday night.



Two needle-like Geminids flash through the view in this photo taken during the 2012 maximum. Credit: Bob King


Two needle-like Geminids flash through the view in this photo taken during the 2012 maximum. Geminid meteors are markedly slower than the summer Perseids (about half as fast) but have their share of fireballs. Credit: Bob King
Gemini crosses the meridian high in the southern sky for skywatchers at mid-northern latitudes around 2 a.m. this weekend — the time you’d expect to see the most meteors per hour. But hey, who’s counting? Find a location with a wide-open view of the sky and tuck yourself under a sleeping bag in a comfy reclining chair. Creature comforts like coffee or a radio playing softly in the background will make you feel like you never had it so good. Then stare off into space and let come what may.,

Because all shower meteors arrive on parallel paths traveling at the same speed, they appear to radiate from a single point in the sky. The radiant is nothing more than a perspective effect, the very same as railroad tracks appearing to converge in the distance. Meteors near the radiant leave very short trails; the farther away you look, the longer the trail.

It’s not necessary to directly face the radiant because shower meteors appear all over the sky. During the evening, I typically turn my chair to face east-southeast with the radiant off to one side. In the wee hours, with the radiant nearly overhead, I face south instead.

According to the International Meteor Organization (IMO), mass-sorting of debris within the Geminid stream will lead to an abundance of fainter, telescopic meteors about a day prior to visual maximum. If you happen to be out on Dec. 12-13 looking at deep sky objects through your telescope, you might notice a surfeit of faint meteors zipping through the field of view.



Graph of Geminids activity in December 2014 showing a maximum zenithal hourly rate of 253 meteors/hour. Credit: IMO


Graph of Geminids activity in December 2014 showing a maximum zenithal hourly (ZHR) rate of 253 meteors an hour. Observers in the southern hemisphere can also watch the shower, but hourly meteor counts will be much lower (20-30 per hour) because Gemini hunkers low in the northern sky. Credit: IMO
Be sure to watch the IMO Geminid activity website during peak shower activity. Click the live ZHR link and then 2015 Geminids to watch the data flow in from observers around the planet. The IMO invites you to share your observations of the shower by doing a scientific meteor count. Click here for instructions.

Unlike the August Perseids, the Geminid shower is a relative newcomer. It apparently debuted in 1862 when English observer R. P. Greg noticed a new meteor radiant in Gemini active between Dec. 10-12. By the 1870s, more and more astronomers began observing the shower and making counts. Although they “tiptoed in” at first with maxima of 20 meteors per hour in the late 1890s, the shower ramped up to 50 per hour by the 1930s and 80 per hour in the 1970s. Now it’s over a 100.



Time lapse-photo showing geminids over Pendleton, OR. Credit: Thomas W. Earle


Composite image showing Geminids over Pendleton, Oregon. Credit: Thomas W. Earle
Most showers are spawned by bits and pieces of dust and debris that drift away from an active comet to create a stream of orbiting debris. When Earth’s path intersects the stream, dust strikes the atmosphere, heats up and creates a glowing tube of ionized air overhead we call a meteor. The parent of the Geminids was finally tracked down in the 1980s. Surprise! It turned out to be an asteroid — 3200 Phaethon. Debris released by the asteroid, perhaps during its routine close approaches to the Sun, make the Geminids one of only two major showers (the other is the January Quadrantids) to originate from an asteroid.

Consistent and reliable, the Geminid shower is not to miss this year. Clear skies!





About 

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. Every day the universe offers up something both beautiful and thought-provoking. I also write a daily astronomy blog called Astro Bob.

Share this:

Posted by Nelio Inacio at 7:09 AM 0 comments

What Are The Different Parts Of A Volcano?

What Are The Different Parts Of A Volcano?:



Tungurahua volcano. Credit: Patrick Taschler


Tungurahua (“throat of fire”), an active stratovolcano in Ecuador. Credit: Patrick Taschler
Without a doubt, volcanoes are one of the most powerful forces of nature a person can bear witness to. Put simply, they are what results when a massive rupture takes place in the Earth’s crust (or any planetary-mass object), spewing hot lava, volcanic ash, and toxic fumes onto the surface and air. Originating from deep within the Earth’s crust, volcanoes leave a lasting mark on the landscape.

But what are the specific parts of a volcano? Aside from the “volcanic cone” (i.e. the cone-shaped mountain), a volcano has many different parts and layers, most of which are located within the mountainous region or deep within the Earth. As such, any true understanding of their makeup requires that we do a little digging (so to speak!)

While volcanoes come in a number of shapes and sizes, certain common elements can be discerned. The following gives you a general breakdown of a volcanoes specific parts, and what goes into making them such a titanic and awesome natural force.

Magma Chamber: A magma chamber is a large underground pool of molten rock sitting underneath the Earth’s crust. The molten rock in such a chamber is under extreme pressure, which in time can lead to the surrounding rock fracturing, creating outlets for the magma. This, combined with the fact that the magma is less dense than the surrounding mantle, allows it to seep up to the surface through the mantle’s cracks.



Lava cooling after an eruption, Credit: kalapanaculturaltours.com


Lava cooling after an eruption from Kilauea, a shield volcano near Kalapana, Hawaii Credit: kalapanaculturaltours.com
When it reaches the surface, it results in a volcanic eruption. Hence why many volcanoes are located above a magma chamber. Most known magma chambers are located close to the Earth’s surface, usually between 1 km and 10 km deep. In geological terms, this makes them part of the Earth’s crust – which ranges from 5–70 km (~3–44 miles) deep.

Lava: Lava is the silicate rock that is hot enough to be in liquid form, and which is expelled from a volcano during an eruption. The source of the heat that melts the rock is known as geothermal energy – i.e. heat generated within the Earth that is leftover from its formation and the decay of radioactive elements. When lava first erupted from a volcanic vent (see below), it comes out with a temperature of anywhere between 700 to 1,200 °C (1,292 to 2,192 °F). As it makes contact with air and flows downhill, it eventually cools and hardens.

Main Vent: A volcano’s main vent is the weak point in the Earth’s crust where hot magma has been able to rise from the magma chamber and reach the surface. The familiar cone-shape of many volcanoes are an indication of this, the point at which ash, rock and lava ejected during an eruption fall back to Earth around the vent to form a protrusion.

Throat: The uppermost section of the main vent is known as the volcano’s throat. As the entrance to the volcano, it is from here that lava and volcanic ash are ejected.




Thurston lava tube is located on Kilauea in Hawaii. Credit: P. Mouginis-Mark, LPI


Thurston lava tube is located on Kilauea in Hawaii. Credit: P. Mouginis-Mark, LPI
Crater: In addition to cone structures, volcanic activity can also lead to circular depressions (aka. craters) forming in the Earth. A volcanic crater is typically a basin, circular in form, which can be large in radius and sometimes great in depth. In these cases, the lava vent is located at the bottom of the crater. They are formed during certain types of climactic eruptions, where the volcano’s magma chamber empties enough for the area above it to collapse, forming what is known as a caldera.

Pyroclastic Flow: Otherwise known as a pyroclastic density current, a pyroclastic flow refers to a fast-moving current of hot gas and rock that is moving away from a volcano. Such flows can reach speeds of up to 700 km/h (450 mph), with the gas reaching temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill from their eruption site.

Their speeds depend upon the density of the current, the volcanic output rate, and the gradient of the slope. Given their speed, temperature, and the way they flow downhill, they are one of the greatest dangers associated with volcanic eruptions and are one of the primary causes of damage to structures and the local environment around an eruption site.

Ash Cloud: Volcanic ash consists of small pieces of pulverized rock, minerals and volcanic glass created during a volcanic eruption. These fragments are generally very small, measuring less than 2 mm (0.079 inches) in diameter. This sort of ash forms as a result of volcanic explosions, where dissolved gases in magma expand to the point where the magma shatters and is propelled into the atmosphere. The bits of magma then cool, solidifying into fragments of volcanic rock and glass.



Volcanoes


View of volcanic ash spewing from the Eyjafjallajokull volcano in Iceland. Credit: ©Snaevarr Gudmundsson.
Because of their size and the explosive force with which they are generated, volcanic ash is picked up by winds and dispersed up to several kilometers away from the eruption site. Due to this dispersal, ash an also have a damaging effect on the local environment, which includes negatively affecting human and animal health, disrupting aviation, disrupting infrastructure, and damaging agriculture and water systems. Ash is also produced when magma comes into contact with water, which causes the water to explosively evaporate into steam and for the magma to shatter.

Volcanic Bombs: In addition to ash, volcanic eruptions have also been known to send larger projectiles flying through the air. Known as volcanic bombs, these ejecta are defined as those that measure more than 64mm (2.5 inches) in diameter, and which are formed when a volcano ejects viscous fragments of lava during an eruption. These cool before they hit the ground, are thrown many kilometers from the eruption site, and often acquire aerodynamic shapes (i.e. streamlined in form).

While the term applies to any ejecta larger than a few centimeters, volcanic bombs can sometimes be very large. There have been recorded instances where objects measuring several meters were retrieved hundreds of meters from an eruptions. Small or large, volcanic bombs are a significant volcanic hazard and can often cause serious damage and multiple fatalities, depending on where they land. Luckily, such explosions are rare.

Secondary Vent: On large volcanoes, magma can reach the surface through several different vents. Where they reach the surface of the volcano, they form what is referred to as a secondary vent. Where they are interrupted by accumulated ash and solidified lava, they become what is known as a Dike. And where these intrude between cracks, pool and then crystallize, they form what is called a Sill.



Cross-section through a stratovolcano (vertical scale is exaggerated): 1. Large magma chamber 2. Bedrock 3. Conduit (pipe) 4. Base 5. Sill 6. Dike 7. Layers of ash emitted by the volcano 8. Flank 9. Layers of lava emitted by the volcano 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud MesserWoland


Cross-section of a stratovolcano: 1. Magma chamber 2. Bedrock 3. Vent 4. Base 5. Sill 6. Dike 7. Layers of ash 8. Flank 9. Layers of lava 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud. Credit: MesserWoland
Secondary Cone: Also known as a Parasitic Cone, secondary cones build up around secondary vents that reach the surface on larger volcanoes. As they deposit lava and ash on the exterior, they form a smaller cone, one that resembles a horn on the main cone.

Yes indeed, volcanoes are as powerful as they are dangerous. And yet, without these geological phenomena occasionally breaking through the surface and reigning down fire, smoke, and clouds of ash, the world as we know it would be a very different place. More than likely, it would be a geologically dead one, with no change or evolution in its crust. I think we can all agree that while such a world would be much safer, it would also be painfully boring!

We have written many interesting articles about volcanoes here at Universe Today. Here’s is one about the different types of volcanoes, one about composite volcanoes, and here’s one on the famous volcanic belt, the Pacific “Ring of Fire”.

Astronomy Cast also has a lovely episodes about volcanoes and geology, titled Episode 307: Pacific Ring of Fire and Episode 51: Earth

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.





About 

Matt Williams is the Curator of the Guide to Space for Universe Today, a a regular contributor to HeroX, a science fiction author, and a Taekwon-Do instructor. He lives with his family on Vancouver Island in beautiful BC.

Share this:

Posted by Nelio Inacio at 7:08 AM 0 comments

Tuesday, December 8, 2015

MESSENGER Spies a Meteor Shower… on Mercury

MESSENGER Spies a Meteor Shower… on Mercury:



Image credit:


A meteor stream from 2P Encke vs the orbit of Mercury. Image credit: NASA/Goddard, Artist’s concept
Leonid meteor storms. Taurid meteor swarms. Earth is no stranger to meteor showers, that’s for sure. Now, it turns out that the planet Mercury may experience periodic meteor showers as well.

The news of extraterrestrial meteor showers on Mercury came out of the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society currently underway this week in National Harbor, Maryland. The study was carried out by Rosemary Killen of NASA’s Goddard Spaceflight Center, working with Matthew Burger of Morgan State University in Baltimore, Maryland and Apostolos Christou from the Armagh Observatory in Northern Ireland.  The study looked at data from the MErcury Surface Space Environment Geochemistry and Ranging (MESSENGER) spacecraft, which orbited Mercury until late April of this year. Astronomers published the results in the September 28th issue of Geophysical Research Letters.

Micrometeoroid debris litters the ecliptic plane, the result of millions of years of passages of comets through the inner solar system. You can see evidence of this in the band of the zodiacal light visible at dawn or dusk from a dark sky site, and the elusive counter-glow of the gegenschein.



The orbit of comet 2P Encke. Image credit: NASA/JPL


The orbit of comet 2P Encke. Image credit: NASA/JPL
Researchers have tagged meteoroid impacts as a previous source of the tenuous exosphere tails exhibited by otherwise airless worlds such as Mercury. The impacts kick up a detectable wind of calcium particles as Mercury plows through the zodiacal cloud of debris.

“We already knew that impacts were important in producing exospheres,” says Killen in a recent NASA Goddard press release. “What we did not know was the relative importance of comet streams over zodiacal dust.”

This calcium peak, however, posed a mystery to researchers. Namely, the peak was occurring just after perihelion—Mercury orbits the Sun once every 88 Earth days, and travels from 0.31 AU from the Sun at perihelion to 0.47 AU at aphelion—versus an expected calcium peak predicted by researchers just before perihelion.



Image credit:


STEREO A catches sight of comet 2P Encke. Image credit: NASA/STEREO
A key suspect in the calcium meteor spike dilemma came in the way of periodic Comet 2P Encke. Orbiting the Sun every 3.3 years—the shortest orbit of any known periodic comet—2P Encke has made many passages through the inner solar system, more than enough to lay down a dense and stable meteoroid debris stream over the millennia.

With an orbit ranging from a perihelion at 0.3 AU interior to Mercury’s to 4 AU, debris from Encke visits Earth as well in the form of the November Taurid Fireballs currently gracing the night skies of the Earth.

The Encke connection still presented a problem: the cometary stream is closest to the orbit of Mercury about a week later than the observed calcium peak. It was as if the stream had drifted over time…



Image credit:


Comet 2P Encke, captured by NASA’s MESSENGER spacecraft. Image credit: NASA/Johns Hopkins/APL/SW Research Institute
Enter the Poynting-Robertson effect. This is a drag created by solar radiation pressure over time. The push on cometary dust grains thanks to the Poynting-Robertson effect is tiny, but it does add up over time, modifying and moving meteor streams. We see this happening in our own local meteor stream environment, as once great showers such as the late 19th century Andromedids fade into obscurity. The gravitational influence of the planets also plays a role in the evolution of meteor shower streams as well.

Researchers in the study re-ran the model, using MESSENGER data and accounting for the Poynting-Robertson effect. They found the peak of the calcium emissions seen today are consistent with millimeter-sized grains ejected from Comet Encke about 10,000 to 20,000 years ago. That grain size and distribution is important, as bigger, more massive grains result in a smaller drag force.



Image credit: Kevin Palmer


A 2015 Taurid meteor. Image credit: Kevin Palmer
This finding shows the role and mechanism that cometary debris plays in exosphere production on worlds like Mercury.

“Finding that we can move the location of stream to match MESSENGER’s observations is gratifying, but the fact that the shift agrees with what we know about Encke and its stream from independent source makes us confident that the cause-and-effect relationship is real, says Christou in this week’s NASA Goddard press release.



Launched in 2004, MESSENGER arrived at Mercury in March 2011 and orbited the world for over four years, the first spacecraft to do so. MESSENGER mapped the entire surface of Mercury for the first time, and became the first human-made artifact to impact Mercury on April 30th, 2015.

The joint JAXA/ESA mission BepiColombo is the next Mercury mission in the pipeline, set to leave Earth on 2017 for insertion into orbit around Mercury on 2024.

An interesting find on the innermost world, and a fascinating connection between Earth and Mercury via comet 2P Encke and the Taurid Fireballs.





About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

Share this:

Posted by Nelio Inacio at 7:15 AM 0 comments

Cosmologist Thinks a Strange Signal May Be Evidence of a Parallel Universe

Cosmologist Thinks a Strange Signal May Be Evidence of a Parallel Universe:



Image Credit: M. Alvarez, R. Kaehler, and T. Abel


A simulation of the early Universe. Credit: M. Alvarez, R. Kaehler, and T. Abel
In the beginning, there was chaos.

Hot, dense, and packed with energetic particles, the early Universe was a turbulent, bustling place. It wasn’t until about 300,000 years after the Big Bang that the nascent cosmic soup had cooled enough for atoms to form and light to travel freely. This landmark event, known as recombination, gave rise to the famous cosmic microwave background (CMB), a signature glow that pervades the entire sky.

Now, a new analysis of this glow suggests the presence of a pronounced bruise in the background — evidence that, sometime around recombination, a parallel universe may have bumped into our own.

Although they are often the stuff of science fiction, parallel universes play a large part in our understanding of the cosmos. According to the theory of eternal inflation, bubble universes apart from our own are theorized to be constantly forming, driven by the energy inherent to space itself.

Like soap bubbles, bubble universes that grow too close to one another can and do stick together, if only for a moment. Such temporary mergers could make it possible for one universe to deposit some of its material into the other, leaving a kind of fingerprint at the point of collision.

Ranga-Ram Chary, a cosmologist at the California Institute of Technology, believes that the CMB is the perfect place to look for such a fingerprint.



This image, the best map ever of the Universe, shows the oldest light in the universe. This glow, left over from the beginning of the cosmos called the cosmic microwave background, shows tiny changes in temperature represented by color. Credit: ESA and the Planck Collaboration.


The cosmic microwave background (CMB), a pervasive glow made of light from the Universe’s infancy, as seen by the Planck satellite in 2013. Tiny deviations in average temperature are represented by color. Credit: ESA and the Planck Collaboration.
After careful analysis of the spectrum of the CMB, Chary found a signal that was about 4500x brighter than it should have been, based on the number of protons and electrons scientists believe existed in the very early Universe. Indeed, this particular signal — an emission line that arose from the formation of atoms during the era of recombination — is more consistent with a Universe whose ratio of matter particles to photons is about 65x greater than our own.

There is a 30% chance that this mysterious signal is just noise, and not really a signal at all; however, it is also possible that it is real, and exists because a parallel universe dumped some of its matter particles into our own Universe.

After all, if additional protons and electrons had been added to our Universe during recombination, more atoms would have formed. More photons would have been emitted during their formation. And the signature line that arose from all of these emissions would be greatly enhanced.

Chary himself is wisely skeptical.

“Unusual claims like evidence for alternate Universes require a very high burden of proof,” he writes.

Indeed, the signature that Chary has isolated may instead be a consequence of incoming light from distant galaxies, or even from clouds of dust surrounding our own galaxy.

SO is this just another case of BICEP2? Only time and further analysis will tell.

Chary has submitted his paper to the Astrophysical Journal. A preprint of the work is available here.





About 

Vanessa earned her bachelor's degree in Astronomy and Physics in 2009 from Wheaton College in Massachusetts. Her credits in astronomy include observing and analyzing eclipsing binary star systems and taking a walk on the theory side as a NSF intern, investigating the expansion of the Universe by analyzing its traces in observations of type 1a supernovae. In her spare time she enjoys writing about astrophysics, cosmology, environmental science, biology, and medicine, making delicious vegetarian meals, taking adventures with her husband and/or Nikon D50, and saving the world. Vanessa is currently a science writer at Brown University.

Share this:

Posted by Nelio Inacio at 7:14 AM 0 comments
Subscribe to: Posts (Atom)