Solar telescope

From here, astronomers enjoy a view of the seething mass in outer space, located roughly 150 million kilometers away from the earth, with all of its swirls, currents and spots. Some are so large that they would take up our entire planet. And they often cause magnetic storms that can even reach earth. This is when they make the sky glow over the poles. But, severe attacks can also cause damage to satellites, for example, interrupt communication links or take down power lines. To avoid being surprised by unforeseen occurrences like these, astronomers at the BBSO are now keeping a close eye on the sun with their reflector telescope. Technologically speaking, this is a difficult task. Whereas observing the sky at night usually means having to capture every slight beam of light, solar telescopes block out most of the light or focus mainly on select wavelengths within the visible to infrared spectral range, which reduces the heat load on the downstream instrumentation. However, the primary mirror must take the brunt of the sunlight. There is a heat stop at the focus of the primary mirror, which passes light from a small part of the sun and rejects the rest. This makes the heat load tolerable on the next few small mirrors. The rejected heat at the focal point of the primary mirror can get even hotter than an electric iron. This is why powerful ventilators constantly cool off the instruments inside the observatory.