REALLY BLANK SUN: The sun has been blank (no sunspots) for 12 consecutive days. If today ends without a sunspot, the number will increase to 13, matching the longest stretch of blank suns since April of 2010. This is yet another sign that the sunspot cycle is crashing toward a deep minimum expected in 2019-2020. Is space weather coming to an end? On the contrary, now is when things get interesting: Solar Minimum brings extra cosmic rays, pink auroras, and more.
NEUTRONS ON A PLANE: Among researchers, it is well known that air travelers are exposed to cosmic rays. High-energy particles and photons from deep space penetrate Earth's atmosphere and go right through the hulls of commercial aircraft. This has prompted the International Commission on Radiological Protection (ICRP) to classify pilots and flight attendants as occupational radiation workers.
Many studies of this problem focus on ionizing radiation such as x-rays and gamma-rays. On March 16th we turned the tables and measured neutrons instead. During a 12-hour flight from Stockholm to Los Angeles, Spaceweather.com and the students of Earth to Sky Calculus used bubble chambers to monitor neutron activity inside a Scandinavian Airlines jetliner.
In the photo above, taken 35,000 feet above Greenland, each bubble shows where a neutron passed through the chamber and vaporized a superheated droplet. By the time the long flight was over, we measured almost 20 uSv (microsieverts) of radiation from neutrons--similar to the dose from a panoramic X-ray at your dentist's office. This confirms that neutrons are an important form of aviation radiation relevant to both air travelers and future space tourists.
Where do these neutrons come from? Mainly, they are secondary cosmic rays. When primary cosmic rays from deep space hit Earth's atmosphere, they produce a spray of secondary particles including neutrons, protons, alpha particles, and other species. Cosmic ray neutrons can reach the ground; indeed, researchers routinely use neutron counters on Earth's surface to monitor cosmic ray activity above the atmosphere. Now we're doing the same thing onboard airplanes.
Earlier in the week, we flew these bubble chambers to the Arctic stratosphere using a space weather balloon. Interestingly, the 12-hour plane flight yielded ~6 times more neutrons than the shorter (2 hour) but far higher (97,000 ft) balloon flight to the stratosphere. What does it mean? We're still analyzing the data and will have more insights to share in the days ahead. Stay tuned!
Realtime Space Weather Photo Gallery
CORONAL HOLE TURNS TOWARD EARTH: A hole has opened in the sun's atmosphere, and it is turning toward Earth. NASA's Solar Dynamics Observatory is tracking the opening, which researchers call a "coronal hole" (CH):
Coronal holes are places--big places--where the sun's magnetic field opens up and allows solar wind to escape. A wide stream of solar wind flowing from this coronal hole is expected to reach our planet on March 23rd. The impact of the solar wind should produce magnetic activity around Earth's poles and could spark the first auroras of northern spring. Free: Aurora Alerts