April - Astronomical calendar 2023

April: What colour is the Sun?

The Sun is the closest star to the Earth, the only one where we can make out details of its surface. The image shows three versions of the same Sun observed through different filters: the violet image is obtained with a filter centred on a calcium line (3 934 Å); the red image corresponds to a hydrogen line called Ha (6 563 Å); and the green image is obtained through a so-called continuum filter in the middle region of the visible spectrum (5400 Å). Each filter provides complementary information and often different layers of the solar surface are measured. In the violet image, the regions with the strongest magnetic fields stand out brightly; in the green image, the sunspots in the photosphere; and in the red image, the bulges and flares in the solar chromosphere.


Credit: Daniel López / IAC (Solar telescopes UC3 y MUSOL)

April - Astronomical calendar 2023
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Daniel López