DOUBLE STAR IN THE MORNING SKY: Are you up before sunrise? Look east. Venus is passing by 1st-magnitude star Regulus forming a bright "double star" in the waxing twilight sky. The eye-catching close encounter will continue for the next two days. Sky maps: Sept.18, 19, 20.
SOLAR WIND SPARKS AUORAS: For the 5th day in a row, Earth is inside a stream of fast-moving solar wind. It arrived abruptly on Sept. 14th and has been sparking polar auroras ever since. Photographer Yuichi Takasaka of Yellowknife, Canada, was watching a leisurely curtain of light on Sept. 17th when, suddenly, it burst into a spray of rapidly-changing forms:
"The lights were moving so quickly, I had to use very fast shutter speed to record these sequences," he says. "It was an amazing example of auroras breaking up."
The solar wind underlying this display is flowing from a wedged-shaped hole in the sun's atmosphere. We could begin to exit the broad stream later today. NOAA forecasters say this will gradually lessen the odds of geomagnetic storms from 50% on Sept. 19th to only 30% by Sept. 21st. Free: Aurora Alerts
PHYSICS OF AN EXPLODING SPACE WEATHER BALLOON: This month, the students of Earth to Sky Calculus have been launching space weather balloons at a frenetic pace, more than half a dozen so far. Their goal: To monitor the effect of September's surprising solar flares on Earth's upper atmosphere. At the apex of every flight, the balloon explodes and the payload parachutes back to Earth. On Sept. 13th, a new upward-facing camera photographed the pop:
This image illustrates recent findings about the physics of exploding balloons. In Oct. 2015, researchers Sébastien Moulinet and Mokhtar Adda-Bedia of the Ecole Normale Supérieure published a Physical Review Letter entitled "Popping Balloons: A Case Study of Dynamical Fragmentation." In it, they reported the results of a series of fun yet informative laboratory experiments in which one balloon after another was popped and analyzed.
Basically, there are two ways a balloon can pop: along a single seam (the "opening regime") or along many tears (the "fragmentation regime"). This video shows the two regimes in action. Which way the balloon decided to pop depends on the stress in the rubber membrane. When the stress is low, it can be relieved with a single tear, but when the stress is high, many tears are required to do the job.
Clearly, space weather balloons explode in the fragmentation regime. This is hardly a surprise. When space weather balloons are launched, they measure no more than 6 to 8 feet in diameter. By the time they reach the stratosphere, they have stretched into a sphere as wide as a house. That's a lot of tension to release! More information about this research is available from the American Physical Society.
Realtime Space Weather Photo Gallery
ROSE QUARTZ CRYSTAL ECLIPSE PENDANTS: On Aug. 21st during the Great American Solar Eclipse, the students of Earth to Sky Calculus launched 11 space weather balloons from the path of totality. They aimed to photograph the Moon's shadow from the stratosphere--and they succeeded. As a fundraiser, some of the balloons carried jewelry. Here is a rose quartz crystal pendant entering the Moon's shadow more than 90,000 feet above the Malheur National Forest in eastern Oregon:
During the 2.5 hour flight, the pendants were wrapped in the Moon's shadow for more than two minutes, experiencing a spooky darkness colder than -50 C.
You can have one for $149.95. Each crystal pendant comes with a unique gift card showing the jewelry passing through the Moon's shadow and floating at the top of Earth's atmosphere. The interior of the card tells the story of the flight and confirms that this gift has been to the edge of space and back again.
Far Out Gifts: Earth to Sky Store
All proceeds support hands-on STEM education