National Astronomical Observatory of Japan

Solar and Plasma Astrophysics Division : Overview

English / Japanese

Our research targets are solar and astrophysical plasmas.Our activities include observations of the sun with space-borne and ground-based telescopes, instrument development, and theoretical studies.

Hinode Science Center

In close cooperation with the Institute of Space and Astronautical Science (currently ISAS/JAXA), we developed the Bragg crystal spectrometer (SOX) on board 'Hinotori' (launched in 1981) and the soft X-ray telescope (SXT, in cooperation with NASA) and the Bragg crystal spectrometer (BCS, in cooperation with SERC/UK) on board 'Yohkoh', which was launched in 1991. The data from Yohkoh have literally revolutionized our understanding of the solar corona.Yohkoh established that solar flares are definitely due to the process of magnetic field reconnection.Yohkoh also revealed the dynamic nature of the solar corona where micro-flares, X-ray jets, and large-scale restructuring of magnetic fields are seen frequently.

The next mission, Solar-B, was successfully launched on September 23, 2007, and has been given the name 'Hinode' (sunrise). The Hinode satellite investigates the magnetic connections between activities in the corona and their driving sources at the solar surface. The activities in the corona can be observed in X-rays and ultraviolet radiation, while magnetic activity near the solar surface can be measured in the visible wavelengths. The Hinode satellite carrie an X-ray telescope and an ultraviolet instrument, together with an optical telescope equipped with a focal-plane instrument package. The optical telescope onboard Hinode is also be used in studying the formation of elementary magnetic flux tubes and the so-called dynamo process under the visible surface of the sun.

Solar Observatory

Studies of the solar atmosphere and its activity have been conducted with the coronagraphs at the Norikura Observatory and the Solar Flare Telescope at Mitaka. The coronagraph is a telescope specially designed to observe the solar corona. The one at Norikura is equipped with a large spectrograph, and in cooperation with Yohkoh, we have been studying spectroscopically the heating mechanism of the solar corona. The Solar Flare Telescope is a highly automated video vector magnetograph and is measuring the magnetic stress in the solar atmosphere, which is believed to be the energy source of solar flare explosions.

We are also interested in long-term variation of the sun, and the telescopes at Mitaka and Norikura are used to constantly monitor the number and the location of sunspots, the size and the location of flares, the brightness of the corona, and so on. These data are attracting new attention recently in terms of the sun's influence on the environment of the earth.

The magnetic field, which is the source of all the activities on the sun, is believed to be generated by a process called the MHD dynamo, in which combined effects of rotation and convection produces the magnetic field. However, the convective flows that are responsible for the dynamo action have not been detected so far, probably because they are very slow. In order to fully understand the mechanism of solar dynamo, sustained and high accuracy observations of the magnetic and velocity fields of the sun is crucial. We are proposing a new instrument, 'the Solar Cycle Telescope' for this purpose.

Last Update: 2007 May 19