SUNSPOT COUNTS REACH 7-YEAR LOW: The face of the sun has been blank (no sunspots) for 13 consecutive days. The last time this happened was April of 2010, near the end of a deep Solar Minimum. The current stretch of blank suns heralds a new Solar Minimum expected to arrive 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.
INFERIOR CONJUNCTION OF VENUS: On March 25th, Venus will pass almost directly between Earth and the sun--an event astronomers call "inferior solar conjunction." As Venus approaches the sun, the planet is turning its night side toward Earth, reducing its luminous glow to a thin sliver. Shahrin Ahmad of Kuala Lumpur, Malaysia, has been monitoring the transformation:
"The crescent is both narrowing and rotating as Venus approaches inferior conjunction," says Ahmad.
Right now, Venus is plunging toward the sun in the western sky at sunset. As the distance decreases, the crescent of Venus will become increasingly thin and circular. The horns of the crescent might actually touch when the Venus-sun angle is least on March 25th. This is the most beautiful time to observe Venus, but also the most perilous. The glare of the nearby sun magnified by a telescope can damage the eyes of anyone looking through the eyepiece.
Anthony J. Cook of the Griffith Observatory has some advice for observers: "I have observed Venus at conjunction, but only from within the shadow of a building, or by adding a mask to the front end of the telescope to fully shadow the optics from direct sunlight. This is tricky with a refractor or a catadioptric, because the optics start at the front end of the tube. Here at Griffith Observatory, I rotate the telescope dome to make sure the lens of the telescope is shaded from direct sunlight, even through it means that the lens will be partially blocked when aimed at Venus. With our Newtonian telescope, I add a curved cardboard mask at the front end of the tube to shadow the primary mirror."
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!
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