The spectral distribution of extraterrestrial radiation refers to the variation in solar irradiance with wavelength of sunlight outside Earth’s atmosphere. It spans a wide range of the electromagnetic spectrum and plays a crucial role in understanding solar energy availability and its interaction with the Earth’s atmosphere.
Definition
- Extraterrestrial radiation is the solar radiation received at the top of Earth’s atmosphere.
- The radiation spectrum varies from 0.1 µm to 100 µm, covering ultraviolet (UV), visible, and infrared (IR) regions.
Spectral Regions
| Region | Wavelength Range | Description / Importance |
|---|---|---|
| 1. UVC | 0.1 µm – 0.28 µm | High-energy radiation, completely absorbed by atmosphere. |
| 2. UVB | 0.28 µm – 0.315 µm | Partially absorbed; contributes to ozone formation. |
| 3. UVA | 0.315 µm – 0.4 µm | Least absorbed UV, penetrates skin, used in therapy. |
| 4. Visible Light | 0.38 µm – 0.78 µm | Visible to the human eye; major contributor to solar energy. |
| 5. Infrared (IR) | 0.7 µm – 100 µm | Perceived as heat; contributes to Earth’s surface heating. |
Sub-Divisions of Infrared Radiation
- IR-A: 0.7 µm – 1.4 µm
- IR-B: 1.4 µm – 3.0 µm
- IR-C: 3.0 µm – 100 µm
These contribute to thermal energy received by the Earth.
Biological Relevance
- UVB & UVA (0.28–0.4 µm): Major contributors to skin damage and biological effects.
- Visible light (0.38–0.78 µm): Safe for human exposure; drives photosynthesis.
- IR radiation (above 0.7 µm): Responsible for heat, but not strongly linked to skin cancers.
