Hole in the Sun

This ominous, dark shape sprawling across the face of the Sun is a coronal hole -- a low density region extending above the surface where the solar magnetic field opens freely into interplanetary space. Studied extensively from space since the 1960s in ultraviolet and x-ray light, coronal holes are known to be the source of the high-speed solar wind, atoms and electrons which flow outward along the open magnetic field lines.

During periods of low activity, coronal holes typically cover regions just above the Sun's poles. But this extensive coronal hole dominated the Sun's northern hemisphere earlier this week, captured here in extreme ultraviolet light by cameras onboard the Solar Dynamics Observatory. The solar wind streaming from this coronal hole triggered auroral displays on planet Earth.

Sunspots Squeeze and Stretch the Day

Most of us don't notice it, but not all days are the same length. Now it seems that sunspots -- dark regions that emerge on the sun's surface -- may be partly responsible for the millisecond fluctuations in the time it takes Earth to rotate once on its own axis. The finding could help to steer spacecraft more accurately.

Researchers have long observed that the spin rate fluctuates with the seasons, in response to shifting wind patterns. Now, a team led by Jean-Louis Le Mouël at the Paris Institute of Geophysics in France has found that this seasonal effect also grows and shrinks in an 11-year cycle, rather like sunspots. Seasons have a bigger effect on spin rate when sunspots are scarce, and a smaller effect when spots are abundant, according to an analysis of data from 1962 to 2009.

Distant Star's Sound Waves Cycle Similar to Sun's

In a bid to unlock longstanding mysteries of the Sun, including the impacts on Earth of its 11-year cycle, an international team of scientists has successfully probed a distant star. By monitoring the star's sound waves, the team has observed a magnetic cycle analogous to the Sun's solar cycle.

The scientists studied a star known as HD49933, which is located 100 light years from Earth in the constellation Monoceros, the Unicorn, just east of Orion. The team examined the star's acoustic fluctuations, using a technique called "stellar seismology." They detected the signature of "starspots," areas of intense magnetic activity on the surface that are similar to sunspots. While scientists have previously observed these magnetic cycles in other stars, this was the first time they have discovered such a cycle using stellar seismology.

Jupiter Struck for Third Time in 13 Months

For the third time in just over a year, amateur astronomers have detected a comet or asteroid strike on Jupiter. The observations, made possible by the widespread use of astronomical video recordings, show that impacts on the giant planet occur more frequently than previously thought.

On Friday, a small comet or asteroid slammed into Jupiter's atmosphere, producing a brief fireball that was independently recorded by two Japanese amateur astronomers taking video through their telescopes.

Rich Exoplanet System Discovered

Astronomers have discovered a planetary system containing at least five planets that orbit a star called HD 10180, which is much like our own Sun. Christophe Lovis from Geneva University's observatory in Switzerland was lead researcher on the study. He said that his team had probably found "the system with the most planets yet discovered".

So far, the astronomers have picked up clear signals from five planets, along with two slightly "fuzzier" signals. One of these possible sixth and seventh planets was estimated to be just 1.4 times the mass of the Earth; if its presence in the system was confirmed, it would be the lowest mass exoplanet yet discovered.

Solar System Slips Back in Time

Without celebrating a birthday, the solar system just got hundreds of thousands of years older. Audrey Bouvier at Arizona State University in Tempe, and colleagues, have analysed inclusions in a meteorite that fell to Earth in north-west Africa in 2004.

Based on the extent to which uranium-238 and uranium-235 isotopes had decayed into their daughter isotopes lead-207 and lead-206, they say the solar system is 4.5682 billion years old. That's between 0.3 and 1.9 million years older than previous estimates, which relied on the Efremovka and Allende meteorites found in Kazakhstan in 1962 and Mexico in 1969, respectively.

Moon May Be Shrinking Very, Very Slowly

New research indicates cracks in the moon's crust that have formed as the interior has cooled and shrunk over the last billion years or so. That means the surface has shrunk, too, though not so you'd notice just from gazing at it. Scientists have identified 14 landforms called lobate scarps scattered over the surface of the moon, explained Thomas R. Watters of the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum.

The scarps had previously been noted at the moon's equator, but this is the first evidence in other areas, indicating they result from a global process. The study calls the scarps "evidence of recent thrust faulting on the moon." But this is planetary science, where "recent" can mean a billion years ago. The size of the scarps indicates a shrinkage in the size of the moon of about 100 meters (328 feet), which wouldn't be nearly enough to be noticed with the naked eye.

Magnetic Mega-star Challenges Black Hole Theory

A neutron star with a mighty magnetic field has thrown down the gauntlet to theories about stellar evolution and the birth of black holes, astronomers reported on Wednesday. The "magnetar" lies in a cluster of stars known as Westerlund 1, located 16,000 light years away in the constellation of Ara, the Altar.

Within Westerlund 1 is the remains of one of galaxy's few magnetars -- a particular kind of neutron star, formed from the explosion of a supernova, that can exert a magnetic field a million, billion times strong than Earth's.

Perseid Meteor Shower Reaches Second Day

Skywatchers have enjoyed another night of "fantastic views" as the annual Perseid meteor shower reached the second day of its peak. The shower was expected to produce a display of up to 80 meteors per hour, according to NASA.

"A waxing crescent moon will set before the shower becomes active, setting a perfect stage for meteor watching," said the US space agency. Space enthusiasts in the UK and US have already captured images of the show.

Huge Solar Storm Triggers Unusual Auroras

Last week's northern lights—which lasted a few days—were products of a large burst of plasma, or charged gas, from the sun known as a coronal mass ejection. A NASA orbiter called the Solar Dynamics Observatory saw last Sunday's eruption, which was aimed directly at Earth and sparked predictions of a shimmering sky show.

Now it seems aurora fans may be in for another treat: A solar flare spotted Saturday by NASA's Solar and Heliospheric Observatory was even more powerful than the previous eruption. Although this time the bulk of the plasma burst isn't aimed right at Earth, scientists say it could still trigger another round of colorful auroras.

Northern Lights Show Signals Sun Is Waking Up

Skywatchers at high latitudes could be in for a spectacular treat of northern lights, the aurora borealis, Tuesday and Wednesday: After a relatively quiet stretch, it appears the sun is ramping up its activity. The sun's surface erupted early Sunday, blasting tons of plasma (ionized atoms) into space. These atoms are headed toward Earth and could create a stunning light show in the process.

The solar eruption, called a coronal mass ejection, was spotted by NASA's Solar Dynamics Observatory , which captures high-definition views of the sun at a variety of wavelengths. SDO was launched in February and peers deep into the layers of the sun, investigating the mysteries of its inner workings.