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About These Images



Image of the Yohkoh satellite rocket launch

Launching Yohkoh

Where do they come from?
The images used in this activity are all from a Japanese satellite called Yohkoh ("sunbeam"), built in cooperation with NASA. Yokoh is designed to give scientists fantastic, detailed images of the sun at the right wavelengths for different kinds of light.

The visible light images came from a camera on board Yohkoh. They are made daily for comparison purposes.
Taking an x-ray picture
Yohkoh's Soft X-ray Telescope (SXT), shown at right, produces the data from which our x-ray images are made. The telescope's mirrors make an x-ray picture of the sun on a flat detector, which is divided into tile-like pixels. Each image is sent back to scientists as a table of numbers that tell how many x-rays landed in each pixel.

Image of the Soft x-ra Telescope (SXT) team with the finishied telescope

The Soft X-ray Telescope, or SXT


Yohkoh X-ray Images Throughout the Solar Cycle - from solar minimum to solar maximum

Image series from solar minimum to solar maximum

Making the daily images
To make each day's image, several images are added together. Each daily image clearly shows the real changes in the Sun since the previous day's image. In this way, the effect of an entire solar cycle can be made visible.
What Do They Show Us?
Visible light images, also called "white light" images, show us the sun's surface, or photosphere, at about 6000 degrees Kelvin. Dark sunspots appear where magnetic fields are very strong. Images from the peak of a solar activity cycle have (by definition) the most sunspots.
Solar image in visible white light
An x-ray image of the sun SXT's X-ray images capture high-energy solar radiation that is normally invisible to the human eye (like the light used to make medical x-rays). The X-ray view is a snapshot of the solar corona, about 1000 to 1,000,000 km above the surface, at temperatures of millions of degrees, rather than the "mere" 6,000 degrees of the photosphere.


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