The Earth's atmosphere absorbs electromagnetic radiation - Edexcel - GCSE Physics - Question 6 - 2012 - Paper 1

Radio telescopes do not have to be placed high up a mountain because radio waves can penetrate the atmosphere more easily than visible light. Thus, they are less affected by atmospheric interference, allowing for effective observation from lower altitudes.

Scientists had to wait for the development of space flight because cosmic background radiation, predicted to have a wavelength of about 1 mm, is absorbed by the Earth's atmosphere. Prior to space flight, measurements from the ground were not possible, as the atmosphere obstructs and distorts these wavelengths. Therefore, with the capability to launch instruments above the atmosphere, scientists could finally collect accurate data regarding this radiation.

When a galaxy has a very large red-shift, its light is shifted to longer wavelengths, potentially into the infrared or radio parts of the spectrum. The Earth's atmosphere absorbs much of this longer wavelength radiation, making it difficult or impossible to detect these signals using ground-based observation.

Careful observation of electromagnetic radiation from distant galaxies has revealed a consistent red-shift across the spectrum, indicating that galaxies are moving away from us. This red-shift supports the Big Bang Theory by suggesting that the Universe is expanding. Additionally, the cosmic microwave background radiation, uniformly detected throughout space, serves as residual evidence from the early, hot stages of the Universe, providing further substantiation to the Big Bang Theory. The spectrum of the radiation matches predictions from the model, reinforcing the understanding of cosmic evolution.