why was it not known until 1955 that the sun sends x-rays to the earth?

The detection of X-rays from the Sun was not possible until 1955 because X-rays are absorbed by the Earth's atmosphere, preventing them from reaching the surface. Early astronomical observations were limited to visible light and other longer wavelengths. It wasn't until the launch of high-altitude balloons and later spacecraft equipped with X-ray detectors that scientists could measure solar X-ray emissions directly, leading to the discovery in 1955. This breakthrough expanded our understanding of solar activity and its impact on space weather.