Feb. 21, 2019: On Nov. 14, 2018, the students of Earth to Sky Calculus launched a space weather balloon to measure increasing levels of cosmic rays in the atmosphere. At the apex of the flight, the balloon exploded and the radiation sensors parachuted back to Earth. A video camera on top of the payload recorded the pop:
These images illustrate recent findings about the physics of exploding balloons. In a Physical Review Letter entitled “Popping Balloons: A Case Study of Dynamical Fragmentation,” researchers from the Ecole Normale Supérieure in Paris report a series of laboratory experiments in which one balloon after another was popped and analyzed.
Basically, there are two ways a balloon can pop: along a single tear (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.
Space weather balloons explode in the fragmentation regime, and the new research explains why. 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. So much stress requires many tears to release.
More information about this research is available from the American Physical Society.
Feb. 21, 2019: Cosmic rays in the stratosphere are intensifying for the 4th year in a row. This finding comes from a campaign of almost weekly high-altitude balloon launches conducted by the students of Earth to Sky Calculus. Since March 2015, there has been a ~13% increase in X-rays and gamma-rays over central California, where the students have launched hundreds of balloons.
The grey points in the graph are Earth to Sky balloon data. Overlaid on that time series is a record of neutron monitor data from the Sodankyla Geophysical Observatory in Oulu, Finland. The correlation between the two data sets is impressive, especially considering their wide geographic separation and differing methodologies. Neutron monitors have long been considered a “gold standard” for monitoring cosmic rays on Earth. This shows that our student-built balloons are gathering data of similar quality.
Why are cosmic rays increasing? The short answer is “Solar Minimum.” Right now, the 11-year solar cycle is plunging into one of the deepest minima of the Space Age. The sun’s weakening magnetic field and flagging solar wind are not protecting us as usual from deep-space radiation. Earth to Sky balloon launches in multiple countries and US states show that this is a widespread phenomenon.
Cosmic rays are of interest to anyone who flies on airplanes. The International Commission on Radiological Protection has classified pilots as occupational radiation workers because of cosmic ray doses they receive while flying. A recent study by researchers at the Harvard School of Public Health shows that flight attendants face an elevated risk of cancer compared to members of the general population. They listed cosmic rays as one of several risk factors. There are also controversial studies that suggest cosmic rays promote the formation of clouds in the atmosphere; if so, increasing cosmic rays could affect weather and climate.
Feb. 17, 2019: On Monday night, Feb. 18th, the brightest star in the night sky will disappear. It’s a rare eclipse of Sirius by asteroid 4388 Jürgenstock. As recently as two days ago, specialists thought the eclipse would be visible in a narrow corridor cutting across the central USA. New calculations, however, suggest a different path:
Sirius’s shadow will cross southern parts of Chile and Argentina, Central America and the Caribbean. This will happen on Feb. 18th between 09:11 pm PST and 09:27 pm PST.
According to David Dunham of the International Occultation Timing Association, the eclipse could last for as much as 1.8 seconds, with Sirius fading to minimum brightness for 0.2 seconds of that time. The angular diameter of Sirius is 0.006 arcseconds. Asteroid Jürgenstock is just a little wider: 0.007 arcseconds, so theoretically Sirius should be completely blocked. “But the asteroid may be a little larger or smaller than predicted, and it’s likely to be irregularly-shaped, so there is a good chance that even at the center, the star will not completely disappear,” notes Dunham.
Named after Venezuelan astrometrist Jürgen Stock, asteroid 4388 Jürgenstock orbits the sun in the inner regions of the asteroid belt between Mars and Jupiter. It is approximately 5 kilometers (3.1 miles) in diameter. Video recordings of the eclipse could help trace the shape of the distant space rock.
Resources: finder charts, observing tips, eclipse home page.