Purple Sun
June 18, 2013
Photographer: Alvaro Ibanez Perez; Alvaro's Web site
Summary Author: Alvaro Ibanez Perez
The image above shows the Sun as a purple disk because it was
taken in ionized calcium light. This is light from calcium atoms that have lost
an electron. It peaks in the violet part of the spectrum (393.4 nm) and is
sensitive to magnetic fields -- magnetically active structures are easier to
detect in this spectral band. Moderate magnetic fields show up brightly (hot),
whereas high magnetic fields are quite dark (cool). The brightest regions are
found in the chromosphere and are known as "plages." The darkest
regions are sunspots on the Sun's photosphere. These spots are approximately
1,500 - 2,000 K cooler than their surroundings. Over much of the photosphere granulation
can also be identified.
On the left edge of the disk (at center), note the bright solar prominence, and
on the right edge there’s an incredible solar flare equivalent to 25 Earths in
length. This huge flare lasted only about 25 minutes. Image acquired on May 13,
2013.
Photo details: Image made with a Coronado PST CaK solar telescope; bandwidth of 2.2 angstroms centered at 393.4 nm (very dim). QHY5-II camera -- monochrome.