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During solar minimum, when the sun is devoid of sunspots, the Sun twinkles with X-Ray Bright Points (XBPs). The short-lived phenomena were first observed in 1969 and are now thought to always be present on the Sun.
Early on, it was observed that the number of XBPs increased as the number of sunspots decreased on the sun. But a study done with Yohkoh, Hinode's predecessor, found that the observed increase in XBPs is due to a decrease in the Sun's X-ray background intensity and not due to the number of sunspots on the Sun.
When the Sun is covered in sunspots, they are very bright sources of X-Rays. This causes a thick, dense, canopy of bright X-ray emission to cover most of the Sun. These bright regions make it difficult to observe the twinkling of an XBP.