One of the brightest and most variable UV emissions in the solar system comes from Jupiter's UV aurora. The auroras have been imaged with each camera on HST, starting with the pre-COSTAR FOC and continuing with increasing sensitivity to the present with STIS. This paper presents a short overview of the scientific results on Jupiter's aurora obtained from HST UV images and spectra, plus a short discussion of Saturn's aurora.

The Earth's aurora: Present understanding

With a long history of ground-based and spacecraft measurements, we now have some understanding of the physics of the Earth's auroral processes. A general picture of the nature of auroral activity on the Earth has evolved, without a complete understanding of the many details. In general, auroral emissions are produced by high energy charged particles precipitating into the Earth's upper atmosphere from the magnetosphere (the region of space where the motions of particles are governed by the Earth's magnetic field). It is well established that the Earth's auroral activity is related to solar activity, and more specifically to conditions in the solar wind reaching the Earth. The precipitating charged particles are accelerated to high energies in the Earth's magnetosphere, with some acceleration occurring in the magnetotail region and some occurring by fieldaligned potentials in the topside ionosphere.