'Sun Dog' appears in the sky

Drinkers at Havana's famous saloon bar Sloppy Joe's can't believe their eyes as 'sun dog' appears in the sky

Those having a beer at Sloppy Joe's Bar in Havana Cuba 13 April 2013, will be hoping they wake up tomorrow remembering their time there.

For above the newly-refurbished and somewhat iconic bar, high in the sky occurred an atmospheric phenomenon known as a 'sun dog'.

The sun was surrounded by a bright ring, caused by a refraction of sunlight by small ice crystal in the atmosphere.

Bright spark: An atmospheric phenomenon known as a 'sun dog' is seen in the sky over Sloppy Joe's Bar, Havana, Cuba

The 'sun dogs' are red in shape, and they number around the outside of the sun, joined together by a white circle that is often labelled a 'Mock Sun'.

This event normally occurs when the sun is low, although it can happen at other times of the day, but the 'dogs' will be less striking and probably not as bright.

Put down your pint: The rare halo around the sun is caused by the refraction of sunlight by small ice crystals in the atmosphere

It is the crystals that refract the sun's light at an angle of 22 degrees. However as the crystals lower and disperse, they become vertically aligned, striking the light horizontally, and this is how the sun dogs are formed.

The famous old-town saloon bar, once frequented by the likes of John Wayne, Spencer Tracy and Clark Gable, has only just reopened after 50 years.

It's a sign: Sloppy Joe's will be hoping the act of nature above its very own roof can bring it good luck

And the new owners will be hoping the fantastic spectacle seen above the bar will be a sign of good things to come.

Careful: People look up to the sky, though with a hand for a shield as the sun dog is particularly bright

Sun dogs are visible all over the world and at any time of year regardless of the ground level temperature.

In Europe and North America one will be seen on average twice a week if searched for.

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Four asteroids flash past Earth in one day

Earth is experiencing an unusual cosmic bombardment as four large asteroids pass it in just one day. Fortunately astronomers don’t seem to joking when saying none are expected to pose danger.

The largest is 4034 Vishnu, which is 800 meters across – the length of the Burj Khalifa in Dubai – though much greater in mass. In comparison, the Tunguska meteorite that devastated hundreds of miles of Siberian wilderness when it landed in 1908 was estimated to be no bigger than 100 meters. The asteroid that may have led to the extinction of dinosaurs 65 million years ago may have been up to 10 kilometers across.

But Vishnu 4034 – which was discovered in 1986 – will pass nearly 23 million kilometers from the Earth’s surface. The closest of the four, EN 89, will be just over 5 million kilometers away from the planet. The asteroid was only discovered a fortnight ago.

Although in everyday terms, the asteroids, ancient cosmic bodies that did not form into planets, will be a distance away, they are still classed as Close Approaches by astronomers. In total several hundred of them happen each year, but it is unusual for so many passes to happen over the course of one day.

The closest large asteroid to pass Earth this year was the 50-meter DA14, which flew 27,600 kilometers from the surface in February. Remarkably on the same day, an asteroid of up to 20-meters penetrated the atmosphere and exploded over Chelyabinsk in Siberia.

                           Orbit Diagram. Image from nasa.gov

On average, asteroids of that size enter the atmosphere every 10 years. Those such as the Yucatan meteor that may have ended the Mesozoic Era, are expected to impact the Earth once every 20 million years.

While, the paths of many asteroids can be charted centuries ahead (and could even be destroyed if they head for the Earth) many, like the Chelyabinsk Meteor, are not detected until they enter the atmosphere – rendering the planet potentially vulnerable to impacts millions of times more powerful than the worst nuclear explosions.

But, some are taking a more positive attitude to asteroids. Earlier this year, Astrorank, a company that evaluates the make-up of asteroids in view of future space mining operations, said that 4034 Vishnu – which is composed largely of platinum and nickel-iron – is worth around $40 trillion dollars, more than half of the world’s gross national product last year.

   "Are We Entering the Danger Zone?"

Is there a genocidal countdown built into the motion of our solar system? Recent work at Cardiff University suggests that our system's orbit through the Milky Way encounters regular speedbumps - and by "speedbumps" we mean "potentially extinction-causing asteroids".

Professor William Napier and Dr Janaki Wickramasinghe completed computer simulations of the motion of the Sun in our outer spiral-arm location in the Milky Way that revealed a regular oscillation through the central galactic plane, where the surrounding dust clouds are the densest. The solar system is a non-trivial object, so its gravitational effects set off a far-reaching planetoid-pinball machine which often ends with comets being hurled into the intruding system.

                    Number of  NEA is dizzyingly grew in the last three decades

The sun is about 26,000 light-years from the center of the Milky Way Galaxy, which is about 80,000 to 120,000 light-years across (and less than 7,000 light-years thick). We are located on on one of its spiral arms, out towards the edge. It takes the sun -and our solar system- roughly 200-250 million years to orbit once around the Milky Way. In this orbit, we are traveling at a velocity of about 155 miles/sec (250 km/sec).

Many of the ricocheted rocks collide with planets on their way through our system, including Earth. Impact craters recorded worldwide show correlations with the ~37 million year-cycle of these journeys through the galactic plane - including the vast impact craters thought to have put an end to the dinosaurs two cycles ago.

Almost exactly two cycles ago, in fact. The figures show that we're very close to another danger zone, when the odds of asteroid impact on Earth go up by a factor of ten. Ten times a tiny chance might not seem like much, but when "Risk of Extinction" is on the table that single order of magnitude can look much more imposing.

You have to remember that ten times a very small number is still a very small number - and Earth has been struck by thousands of asteroids without any exciting extinction events. A rock doesn't just have to hit us, it has to be large enough to survive the truly fearsome forces that cause most to burn up on re-entry.

Professors Medvedev and Melott of the University of Kansas have a different theory based on the same regular motion. As the Sun ventures out "above" the galactic plane, it becomes increasingly exposed to the cosmic ray generating shock front that the Milky Way creates as it ploughs through space. As we get closer to this point of maximum exposure, leaving the shielding of the thick galactic disk behind, the Kansas researchers hold that the increasing radiation destroys many higher species, forcing another evolutionary epoch. This theory also matches in time with the dinosaur extinction.

Passage DA14 occurred the same day as the Chebarkul hit by another asteroid

Either way, don't go letting your VISA bill run up just yet. "Very close" in astronomical terms is very, very different to "close" in homo sapien time.

The characteristic spiral arms of the Milky Way regions where stars and gas are a little closer together -- waves of higher density than elsewhere in our galaxy's disc. Their additional gravity is normally too weak to alter a star's path by much, but if the star's orbital speed happens to match the speed at which the spiral arm is itself rotating, then the extra force has more time to take effect.

Simulations completed by Rok Roskar of the University of Zurich, Switzerland, show that a lucky star can ride the wave for 10,000 light years or more. Our sun is an example, with some measurements implying that the sun is richer in heavy elements than the average star in our neighbourhood, suggesting it was born in the busy central zone of the galaxy, where stellar winds and exploding stars enrich the cosmic brew more than in the galactic suburbs. The gravitational buffeting the solar system received then might also explain why Sedna, a large iceball in the extremities of the solar system, travels on a puzzling, enormously elongated orbit (arxiv.org/abs/1108.1570).

The cosmic panorama at top of page is courtesy of the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) project and the Spitzer Space Telescope. The galactic plane itself runs through the middle of the false-color view. Spitzer's infrared cameras see through much of the galaxy's obscuring dust revealing many new star clusters as well as star forming regions (bright white splotches) and hot interstellar hydrogen gas (greenish wisps). The pervasive red clouds are emission from dust and organic molecules, pocked with holes and bubbles blown by energetic outflows from massive stars. Intensely dark patches are regions of dust too dense for even Spitzer's infrared vision to penetrate.

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