Space Astrophysics

Abstract

The infrared spectrum begins at a end of the visible spectrum at the wavelength of about 1 μm (i.e. 10,000 Å) and stretches over more than ten octaves to about 1 mm where it overlaps the shortest wavelengths of the microwave radio region of the electromagnetic spectrum (Figure 8.1.1). This large region is divided into roughly three regions, namely the near infrared (1–3 μm), the intermediate IR (3–5 μ) and the far IR (5 to ∼ 200 fim). In this broad region of wavelengths lie the characteristic black body radiation of the moon and the planets, cool stars, proto star clouds as well as the cosmic background radiation of the universe. Any object having a temperature in the region of 3K to 300K is suitable for observations at infrared wavelengths. In the field of molecular spectroscopy, the vibrational-rotational bands and lines of many chemically active molecules lie in the infrared region.