The Yohkoh Observatory
How Yohkoh Images the Sun
The Yohkoh Observatory
How Yohkoh Images the Sun
The SXT takes images using a digital camera. The SXT sees the whole Sun at the same time with a resolution of about 5 arcseconds. This means that the SXT can see structures as small as 3500 km across. SXT also has the ability to extract a portion of the image at a higher resolution (2.5 arcseconds) allowing us to see structures as small as 1760 km. The former is known as a full frame image:
SXT Full frame image
which is used to show how the whole Sun is behaving. In this picture we can see a nice big active region in the lower half of the Sun and two more in the upper part. An active region is the name given to that part of the hot solar atmosphere which lies above a sunspot. When a portion of the image is extracted at higher resolution it is known as a partial frame image:
SXT Partial frame image
In this picture we see a close-up of the active region in the lower half of the Sun. On close inspection, the active region is seen to be made up of elongated structures called coronal loops.
SXT can look at the Sun using different filters, in a similar way that we can see different colours. If we put a red filter (some transparent red plastic for example) in front of our eyes, we see only the red parts of what we are looking at. SXT uses specially designed filters to see different X-ray energies. Because of the high energy of the X-ray radiation the filters have to be made of thin sheets of metal (mostly aluminium).
Each different filter allows us to look at different temperatures in the Sun. Using different filters we can measure how hot different parts of the Sun are. In both of the pictures above the bright orange and white colours correspond to temperatures of about 3 million degrees.
Now what? Try looking in the Yohkoh gallery or at some Yohkoh movies, or if you have internet access you can visit the Yohkoh homepage where you will find more information, images and movies.