The year 1999 is therefore a particularly appropriate one in which to review the current state of infrared astronomy. To the astronomer, the infrared region offers substantial advantages.
Interstellar extinction is a very steep function of wavelength.
Heavily obscured regions, such as the centres of galaxies and star-formation regions, cannot be observed at optical wavelengths but are readily studied in the infrared. Planets, circumstellar discs, protostars and other warm objects emit negligible flux at visible wavelengths, and can therefore only be directly observed at infrared wavelengths and longer. Better spatial resolution under seeing-limited conditions. The diameter of an image under seeing limited conditions goes as . In addition, adaptive optics correction becomes much simpler and much more effective as the wavelength increases.