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Category Archives: 10. Our star: the Sun

Millions of people across Indonesia and the Central Pacific have witnessed a total solar eclipse. Because the eclipse path crossed the International Date Line, in the local time zones it began early on Wednesday, March 9, and ended late on Tuesday, March 8.




The Cosmos author, Jay M. Pasachoff, shares his view of totality from the south side of Ternate, in the Maluku Islands of eastern Indonesia:

“All the eclipse phenomena were visible: diamond ring, Baily’s beads, prominences (with a particularly bright prominence at the 9 o’clock position) and the corona, but through thin clouds.”


Credit: Jay M. Pasachoff

Different views of the eclipse provided the Astronomy Picture of the Day (APOD) on March 10, 11, and 12: wide angle view, looking down from NASA’s DISCOVR satellite, and a low-resolution flash spectrum.


The American Association of Physics Teachers have collated a set of educational resources on “Neutrinos: Teaching the science behind the 2015 Nobel Prize in Physics” (see The Cosmos, Section 12.7, pp. 322-325).

Find out more on their website.



The 2015 Nobel Prize in Physics was given on October 6 to Takaaki Kajita of the Superkamiokande experiment and to Arthur McDonald of the Sudbury Neutrino Observatory.  The work at both those sites is thoroughly discussed in The Cosmos (see Section 12.7, p. 322-325) about the solar-neutrino experiment.


By showing definitively that a mix of the three types of neutrinos reaches the Earth, combining the knowledge that only electron-neutrinos leave the Sun shows that neutrinos change in type en route.  Only if neutrinos have mass can such changes take place, so the discovery is a major challenge to the Standard Model of particle physics.

This is the third Nobel Prize for neutrino research.  Half the 1995 Nobel Prize went Fred Reines for the discovery of neutrinos in an atomic-reactor beam (his co-discoverer, Clyde Cowan, having died before the prize was given, making him ineligible).  Half the 2002 Nobel Prize went to Ray Davis, who ran the chlorine version of the neutrino experiment at the Homestake Mine, and Masatoshi Koshiba, who was in charge of Kamiokande (the Neutrino Detection Experiment [NDE] in the Kamioka mine in Japan). John Bahcall from the Institute for Advanced Study, who had done the bulk of the theoretical work involved, was omitted from the prize, unfortunately (again, as the prize is not awarded posthumously).

Links: 2015 Nobel Prize in Physics at the Royal Swedish Academy of Sciences; Dennis Overbye’s analysis for the NY Times (including a discussion of the next investigations via The Deep Underground Neutrino Experiment, DUNE).

A careful restudy of the sunspot numbers reported by dozens of solar observatories around the globe and averaged in the Solar Influences Data Analysis Center at the Royal Observatory of Belgium has found some discrepancies, often based on individual observers’ idiosyncrasies. (See Section 10.2, p. 265 and Figure 10-18a, p. 268.)

The Center has provided the following revised sunspot count for this revision of The Cosmos, 4th ed.  It is updated, too, past the recent solar maximum, which peaked at different times in different solar hemispheres.


Credit: SIDC, Royal Observatory of Belgium

Links: Read more about their analysis and download comparison figures.

From a NuSTAR mission press release:

A mission designed to set its eyes on black holes and other objects far from our solar system turned its gaze back closer to home, capturing images of the Sun. In December 2014, NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, took its first picture of the Sun, producing the most sensitive solar portrait ever taken in high-energy x-rays.


Credit: NASA/JPL-Caltech

While the sun is too bright for other telescopes such as NASA’s Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors. The Sun is not as bright in the higher-energy x-rays detected by NuSTAR, a factor that depends on the temperature of the Sun’s atmosphere.

This first solar image from NuSTAR gives insight into questions about the remarkably high temperatures that are found above sunspots. Future images will provide even better data as the Sun winds down in its solar cycle, with the potential to capture hypothesized nanoflares – smaller versions of the Sun’s giant flares that erupt with charged particles and high-energy radiation.

Links: NuSTAR press release, full-view image of the Sun’s disk.

From a Fremilab press release, April 22, 2015:

The Italian ICARUS neutrino experiment – the world’s largest of its type – will move to Fermilab and become an integral part of the future of neutrino research in the United States (see Section 12.7c, p. 324-325).

Scientists will transport the liquid-argon neutrino detector across the Atlantic Ocean to its new home at the U.S. Department of Energy’s Fermi National Accelerator Laboratory. The 760-ton, 65-foot-long detector took data for the ICARUS experiment at the Italian Institute for Nuclear Physics’ (INFN) Gran Sasso National Laboratory in Italy from 2010 to 2014, using a beam of neutrinos sent through the Earth from CERN. The detector is now being refurbished at CERN, where it is the first beneficiary of a new test facility for neutrino detectors.


Credit: INFN

When it arrives at Fermilab, the detector will become part of an on-site suite of three experiments dedicated to studying neutrinos, ghostly particles that are all around us but have given up few of their secrets. All three detectors will be filled with liquid argon, which enables the use of state-of-the-art time projection technology, drawing charged particles created in neutrino interactions toward planes of fine wires that can capture a 3-D image of the tracks those particles leave. Each detector will contribute different yet complementary results to the hunt for a fourth type of neutrino.

Many theories in particle physics predict the existence of a so-called “sterile” neutrino, which would behave differently from the three known types and, if it exists, could provide a route to understanding the mysterious dark matter that makes up 25 percent of the Universe. Discovering this fourth type of neutrino would revolutionize physics, changing scientists’ picture of the Universe and how it works.

Links: Fermilab press release, CERN press release, ICARUS home.

Adapted from an NOAA press release, February 11, 2015:

On February 11, the United States Air Force launched a National Oceanic and Atmospheric Administration (NOAA) satellite called Deep Space Climate Observatory, or DSCOVR, into orbit. NOAA will use DSCOVR to monitor the solar wind and forecast space weather at Earth — effects from the material and energy from the Sun that can impact our satellites and technological infrastructure on Earth.

Data from DSCOVR, coupled with a new forecast model, will enable NOAA forecasters to predict geomagnetic storm magnitude on a regional basis. Geomagnetic storms occur when plasma and magnetic fields streaming from the Sun impact Earth’s magnetic field. Large magnetic eruptions from the sun have the potential to bring major disruptions to power grids, aviation, telecommunications, and GPS systems.


The DSCOVR mission is a partnership between NOAA, NASA, and the U.S. Air Force.

In addition to space weather-monitoring instruments, DSCOVR is carrying two NASA Earth-observing instruments that will gather a range of measurements from ozone and aerosol amounts, to changes in Earth’s radiation.

Links: original NOAA press release; NY Times article about the launch, DSCOVR home.

The NY Times recently posted a short movie on the Sun: “Out There | Raining Fire” b

Links: the movie on NY Times website; NASA’s Solar Dynamics Observatory home.

From an article in Physics World by Ken Croswell, August 29, 2014:

Physicists working on the Borexino experiment in Italy have successfully detected neutrinos from the main nuclear reaction that powers the Sun. The number of neutrinos observed by the international team agrees with theoretical predictions, suggesting that scientists do understand what is going on inside our star. (See Section 12.7, p. 322.)

Credit: Borexino Collaboration

Credit: Borexino Collaboration

Each second, the Sun converts 600 million tons of hydrogen into helium, and 99% of the energy generated arises from the so-called proton–proton chain. And 99.76% of the time, this chain starts when two protons form deuterium (hydrogen-2) by coming close enough together that one becomes a neutron, emitting a positron and a low-energy neutrino. It is this low-energy neutrino that physicists have now detected. Once this reaction occurs, two more quickly follow: a proton converts the newly minted deuterium into helium-3, which in most cases joins another helium-3 nucleus to yield helium-4 and two protons.

Neutrinos normally pass through matter unimpeded and are therefore very difficult to detect. However, the neutrinos from this reaction in the Sun are especially elusive because of their low energy. The measurement therefore took scientists by surprise.

The Borexino detector is a large sphere containing a benzene-like liquid that is located deep beneath a mountain at the Gran Sasso National Laboratory to shield the experiment from cosmic rays. Occasionally, a neutrino will collide with an electron in the liquid and the recoiling electron will create a flash of ultraviolet light that can then be detected.

Links: the full Physics World article; Borexino website.

The November 11, 2013, Astronomy Picture of the Day shows the total solar eclipse of November 3, as covered by several different solar observatories.


Credit and copyright: D. Seaton (ROB), A. Davis & J. M. Pasachoff (Williams College Eclipse Expedition), NRL, ESA, NASA, NatGeo.

The innermost image shows the Sun in ultraviolet light as recorded over a few hours by ESA’s PROBA2 mission in a Sun-synchronous low Earth orbit. This image is surrounded by a ground-based eclipse image, reproduced in blue, taken from Gabon by Allen Davis and Jay M. Pasachoff during the Williams College Eclipse Expedition. Further out is a circular blocked region used to artificially dim the central Sun by the Large Angle and Spectrometric Coronagraph (LASCO) instrument of the Sun-orbiting SOHO spacecraft. The outermost image – showing the outflowing solar corona – was taken by LASCO ten minutes after the eclipse and shows an outflowing solar corona.

Over the past few weeks, our Sun has been showing an unusually high amount of sunspots, CMEs, and flares – activity that was generally expected as the Sun is currently going through Solar Maximum – the busiest part of its 11 year solar cycle. This image is a picturesque montage of many solar layers at once that allows solar astronomers to better match up active areas on or near the Sun’s surface with outflowing jets in the Sun’s corona.