The year 2008 marks the centenary of the seminal paper by Gustav Mie on electromagnetic scattering by homogeneous spherical particles. Having been cited in almost 4,000 journal articles since 1955 (according to the Science Citation Index Expanded database), Mie s paper has been among the more influential scientific publications of the twentieth century. It has affected profoundly the development of a great variety of natural science disciplines including atmospheric radiation, meteorological optics, remote sensing, aerosol physics, astrophysics, and biomedical optics. Mies paper represented a fundamental advancement over the earlier publications by Ludvig Lorenz in that it was explicitly based on the Maxwell equations, gave the final solution in a convenient form suitable for practical computations, and imparted physical reality to the abstract concept of electromagnetic scattering. The Mie solution anticipated such general concepts as far-field scattering and the Sommerfeld-Silver-Müller boundary conditions at infinity as well as paved the way to such important extensions as the separation of variables method for spheroids and the T-matrix method. Key ingredients of the Mie theory are quite prominent in the superposition T-matrix method for clusters of particles and even in the recent microphysical derivation of the radiative transfer equation. Among the most illustrative uses of the Mie solution have been the explanation of the spectacular optical displays caused by cloud and rain droplets, the identification of sulfuric acid particles in the atmosphere of Venus from Earth-based polarimetry, and optical particle characterization based on measurements of morphology-dependent resonances. Yet it is clear that the full practical potential of the Mie theory is still to be revealed.

The NASA Glory mission is intended to facilitate and improve upon long-term monitoring of two key forcings influencing global climate. One of the mission's principal objectives is to determine the global distribution of detailed aerosol and cloud properties with unprecedented accuracy, thereby facilitating the quantification of the aerosol direct and indirect radiative forcings. The other is to continue the 28-yr record of satellite-based measurements of total solar irradiance from which the effect of solar variability on the Earth's climate is quantified. These objectives will be met by flying two state-of-the-art science instruments on an Earth-orbiting platform. Based on a proven technique demonstrated with an aircraft-based prototype, the Aerosol Polarimetry Sensor (APS) will collect accurate multiangle photopolarimetric measurements of the Earth along the satellite ground track within a wide spectral range extending from the visible to the shortwave infrared. The Total Irradiance Monitor (TIM) is an improved version of an instrument currently flying on the Solar Radiation and Climate Experiment (SORCE) and will provide accurate and precise measurements of spectrally integrated sunlight illuminating the Earth. Because Glory is expected to fly as part of the A-Train constellation of Earth-orbiting spacecraft, the APS data will also be used to improve retrievals of aerosol climate forcing parameters and global aerosol assessments with other A-Train instruments. In this paper, we detail the scientific rationale and objectives of the Glory mission, explain how these scientific objectives dictate the specific measurement strategy, describe how the measurement strategy will be implemented by the APS and TIM, and briefly outline the overall structure of the mission. It is expected that the Glory results will be used extensively by members of the climate, solar, atmospheric, oceanic, and environmental research communities as well as in education and outreach activities.