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(c) ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0
Mosaic of four images taken by Rosetta's navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko. The images used for this mosaic were taken in sequence as a 2×2 raster over an approximately 20 minute period, meaning that there is some motion of the spacecraft and rotation of the comet between the images. The four individual full-frame images are also available as related images below. Note this mosaic has been rotated by 180 degrees and cropped. The mosaic has been put together using Microsoft ICE. This left a few small regions requiring slight exposure adjustments using Adobe Lightroom. The full image has then been lightly contrast enhanced to bring out the activity without increasing the background noise too much.
It was a quiet day on the Sun in September of 2000. The above image from NASA's sun-observing TRACE spacecraft shows, however, that even during "off days" the Sun's surface is a busy place. Shown in ultraviolet light, the relatively cool dark regions have temperatures of thousands of degrees.
A large sunspot group is visible as the bright area near the horizon. The bright glowing gas flowing around the sunspots has a temperature of over one million degrees Celsius (1.8 million degrees Fahrenheit). The high temperatures are thought to be related to the rapidly changing magnetic field loops that channel solar plasma.