Understanding Sunlight

Hanna Strecker is a physicist at the Kiepenheuer Institute for Solar Physics and is a seasoned solar observer. She conducts research into the magnetic fields in the surrounding of sun spots. In Tenerife she performs observations at the Teide Observatory (IAC). She uses GREGOR, Europe’s largest solar telescope, to examine our most important star. She knows all about the sun’s rays and about what determines the strength of the UV radiation.

ZEISS Vision Care: What is light and what is UV radiation?

Hanna Strecker: When we talk about light, we generally mean visible light. Most people are familiar with UV radiation and infrared light. UV radiation is the most high-energy type that reaches us from the sun.

ZEISS Vision Care: What determines the intensity of UV radiation?

Hanna Strecker: The intensity of UV radiation is influenced by the Earth’s atmosphere and the ozone layer, which absorbs a portion of it. What’s more, the intensity of the UV light that reaches us here depends on the position of the sun, which is influenced by the geographical situation, the altitude and the time of day.

ZEISS Vision Care: What’s the difference between perceived heat and UV radiation?

Hanna Strecker: Thermal radiation is what’s known as infrared radiation. UV light behaves in a very different way. For example, when you step into the shade because it’s too hot in the sun, UV light can still reach you by reflecting off the sand, the sea, and especially off snow – so you can still get sunburn.

ZEISS Vision Care: So we even need to take care when it’s cool outside?

Hanna Strecker: Yes. For example, while it may be quite cool 2,400 meters above sea level on the dome of the GREGOR telescope here in Tenerife, a huge amount of UV rays still reach us simply because of the high altitude.