Solar Cycle 24, in X-Ray Vision

By Miles Hatfield
NASA’s Goddard Space Flight Center


September 22, 2018 marked the 12th launch anniversary of Hinode — a solar observatory collaboration between the Japan Aerospace Exploration Agency, the National Astronomical Observatory of Japan, the European Space Agency, the United Kingdom Space Agency and NASA.

Twelve years is long enough for Hinode to observe most of a complete solar cycle. The above image represents Solar Cycle 24 as observed with Hinode’s X-Ray Telescope, or XRT. The XRT observes the Sun’s hot corona, or solar atmosphere, in soft X-rays — wavelengths of light that reveal solar activity reaching tens of millions of degrees Fahrenheit.

The solar cycle refers to an 11-year-long period (on average) during which the Sun’s magnetic field flips — north becomes south, and vice versa — and magnetic activity increases and then decreases. Although driven by the Sun’s internal magnetic dynamo, the progression of the solar cycle is marked by activity visible on its surface and in the corona, including bright solar flares and dark sunspots. The corona, as documented by Hinode’s XRT, reveals an extensive amount about the Sun’s variable activity.

In the graphic above, the farthest (smallest) image is from 2007 and each image increments clockwise by one year. The nearest (largest) image is from 2013, around solar maximum. Note the enhanced presence of bright active regions in the closer images, as the Sun approaches solar maximum. Solar Cycle 24 began on January 4, 2008 with the emergence of a bright active region in the north, and is expected to reach its minimum sometime in 2019.

Hinode’s XRT has taken full-disk synoptic images twice daily for the whole mission (aside from its monthly 3-day maintenance periods).  This long baseline set of measurements extends the cycle of observations from Hinode’s predecessor, Yohkoh, which ended in 2001.

Hinode maintains a polar orbit around Earth from approximately 370 miles altitude, carrying three scientific instruments: the Solar Optical Telescope, the X-ray Telescope, and the Extreme Ultraviolet Imaging Spectrometer.