National Astronomical Observatory of Japan

Sunspot Seen with Millimeter Wave, Calcium Line, and Visible Light


Sunspot Seen with Millimeter Wave, Calcium Line, and Visible Light

From the solar surface to a few thousand kilometers above it, the temperature of the solar atmosphere increases rapidly from around 6,000 degrees to over 1,000,000 degrees, even though this is a very small distance compared to the solar radius (700,000 kilometers). Therefore, when you change the observing wavelength, completely different structures appear. What you can see with millimeter waves and the calcium line is the upper atmosphere, known as the chromosphere, that is about 500 kilometers to 3000 kilometers above the surface. Knowing the energy transmission and thermalization in this layer is thought to be the key to solving the mysteries of the solar corona and chromosphere.

New Eyes to Explore the Sun, Collaboration between the ALMA Antennas and Solar Observation Satellite "Hinode"

The ALMA antennas are radio telescopes for exploring distant objects such as stars and galaxies. But, you can also observe the Sun with ALMA. However, it can’t be observed in the same way as distant celestial bodies, so we needed to solve various problems to observe it. As a result of various efforts, the ALMA antennas started scientific solar observations from 2016. The upper right image of the sunspot was observed by the ALMA antennas in December 2015 to verify the solar observation method. For this verification observation with the ALMA antennas, we performed joint observations with the solar observation satellite "Hinode" (lower right image). We picked the same sunspot and took images of the light emitted by calcium using the Solar Optical Telescope. The light emitted by calcium also emanates from the chromosphere. It occurs in a layer a few hundred kilometers below the millimeter waves observed by the ALMA antennas. You can see that the background changes completely with a slight change in altitude.

Text: Masumi Shimojo (NAOJ Chile Observatory)
Translation by: Hiroko Tsuzuki and Ramsey Lundock (Public Relations Center, NAOJ)

Image Data

Telescope / Instrument / WavelengthALMA / Band 6 Receiver / 1.25 millimeter (239 GHz), Solar observation satellite “Hinode” / Solar Optical Telescope / 396.85 nanometer (Ca II H line), Solar Dynamics Observatory (SDO) / HMI / visible light (continuum)
DateDecember 18, 2015 (ALMA: 19:39 - 20:03 (UT), Solar observation satellite “Hinode”: 19:49:32 (UT), Solar Dynamics Observatory (SDO): 19:48:23 (UT))


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