Solar Observations Begin Second Century
Astrophotography・
The left image is a monochromatic photograph of the Sun taken in the calcium K line (hereinafter, called the “Ca K-line”). It is a digitized photograph taken 100 years ago with a spectroheliograph. At that time, solar observations were performed at Azabu in Tokyo. Regular full-disk solar observation began from this time. And now, 100 years after the first solar observation, we observe the Sun in the Ca K-line using the Solar Flare Telescope in NAOJ Mitaka Campus (right photo).
Solar Ca K-Line Images Taken Recently and 100 Years Ago
The left photo is a monochromatic image of the Sun taken in the Ca K-line 100 years ago on January 20, 1917. The regular full-disk solar observations of NAOJ started from this day (Note). This image of the Sun was taken with a spectroheliograph which performed solar observations at Azabu in Tokyo at that time. With the Ca K-line, we can observe the chromosphere, which is above the solar surface that can usually be seen. The bright white parts are called “plages,” and correspond to active regions. Ca K-line (blue-violet, 393.4 nanometers) is the widest absorption line in the visible light. This wavelength can easily be observed with even a relatively simple spectrograph. Therefore, solar observations at this wavelength were conducted for a long time: 1917 to 1924 in Azabu and from 1925 to 1974 in Mitaka. These observational data are valuable clues to understand the solar activity at that time. After that, the Ca K-line solar observations stopped temporarily. And in July 2015, we restarted observations using the continuum/ G-band/ Ca K-line full-disk imager of the Solar Flare Telescope. This year, 2017, is the 100th anniversary of NAOJ’s solar observations (right photo).
Text by: Kentaro Yaji (Solar Science Observatory, NAOJ)
Translation by: Hiroko Tsuzuki and Ramsey Lundock (Public Relations Center, NAOJ)
(Note) It was known as Tokyo Astronomical Observatory at that time. Back
Image Data
| Object | The Sun |
|---|---|
| Telescope | Grubb 30-centimeter siderostat and Cooke 18-centimeter objective lens |
| Instrument | Spectroheliograph |
| Wavelength | 393.4 nanometers |
| Exposure | unknown |
| Date | January 20, 1917 |
| Credit | National Astronomical Observatory of Japan |
| Object | The Sun |
|---|---|
| Telescope | Solar Flare Telescope |
| Instrument | Continuum/ G-band/ Ca K-line Full-disk Imager |
| Wavelength | 393.4 nanometers |
| Exposure | 20 milliseconds |
| Date | January 21, 2017 |
| Credit | National Astronomical Observatory of Japan |
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Related Links
- Calcium K-line Full-Disk Spectroheliograms from the Solar Activity Database (Solar Science Observatory, NAOJ)
- Topics No.3: The Taisho Era Sun Revived ~ Calcium K-line solar photographs for about 60 years digitized and released ~ (Solar Science Observatory, NAOJ) (Japanese Language Only)
- NAOJ News March 2016 Solar Observatory - Beyond a Century- (Japanese Language Only)