Have you ever seen an entire rainbow? From the ground, typically, only the top portion of a rainbow is visible because directions toward the ground have fewer raindrops. From the air, though, the entire 360 degree circle of a rainbow is more commonly visible. Pictured here, a full circle rainbow was captured over Cottesloe Beach near Perth, Australia last year by a helicopter flying between a setting sun and a downpour. An observer-dependent phenomenon primarily caused by the internal reflection of sunlight by raindrops, the 84-degree diameter rainbow followed the helicopter, intact, for about 5 kilometers. As a bonus, a second rainbow that was more faint and color-reversed was visible outside the first.
The Pacific Ocean and Chilean coast lie below this sea of clouds. Seen through the subtle colors of the predawn sky a lunar eclipse is in progress above, the partially eclipsed Moon growing dark. The curved edge of planet Earth's shadow still cuts across the middle of the lunar disk as the Moon sinks lower toward the western horizon. In fact, from this southern hemisphere location as well as much of eastern North America totality, the Moon completely immersed within Earth's shadow, began near the time of moonset and sunrise on October 8. From farther west the total phase could be followed for almost an hour though, the darker reddened Moon still high in the night sky.
Our view of other star systems just got a little more familiar, with the discovery of a planet 25,000 light-years away that resembles our own Uranus (Voyager 2 image above). Astronomers have discovered hundreds of planets around the Milky Way, including rocky planets similar to Earth and gas planets similar to Jupiter. But there is a third type of planet in our solar system—part gas, part ice—and this is the first time anyone has spotted a twin for our so-called “ice giant” planets, Uranus and Neptune.
While Uranus and Neptune are mostly composed of hydrogen and helium, they both contain significant amounts of methane ice, which gives them their bluish appearance. Given that the newly discovered planet is so far away, astronomers can’t actually tell anything about its composition. But its distance from its star suggests that it’s an ice giant—and since the planet’s orbit resembles that of Uranus, the astronomers are considering it to be a Uranus analog. Regardless, the newly discovered planet leads a turbulent existence: it orbits one star in a binary star system, with the other star close enough to disturb the planet’s orbit.
An international research team led by Radek Poleski, postdoctoral researcher at The Ohio State University, described the discovery in a paper appearing online in TheAstrophysical Journal. The find may help solve a mystery about the origins of the ice giants in our solar system, said Andrew Gould, professor of astronomy at Ohio State.
“Nobody knows for sure why Uranus and Neptune are located on the outskirts of our solar system, when our models suggest that they should have formed closer to the sun,” Gould said. “One idea is that they did form much closer, but were jostled around by Jupiter and Saturn and knocked farther out. Maybe the existence of this Uranus-like planet is connected to interference from the second star,” he continued. “Maybe you need some kind of jostling to make planets like Uranus and Neptune.”
The binary star system lies in our Milky Way galaxy, in the direction of Sagittarius. The first star is about two thirds as massive as our sun, and the second star is about one sixth as massive. The planet is four times as massive as Uranus, but it orbits the first star at almost exactly the same distance as Uranus orbits our sun.
Vous ne pouvez pas créer un sujet. Vous ne pouvez pas éditer les sujets. Vous ne pouvez pas ajouter des sondages. Vous ne pouvez pas attacher des fichiers. Vous ne pouvez pas répondre aux sujets. Vous ne pouvez pas supprimer. Vous ne pouvez pas voter.
Rendez-vous sur C-F.fr
courses-france.com reste en ligne en tant qu'archive mais n'est plus en service.
...dernières nouvelles du cosmos ...
