Mineral dust particles represent the most abundant component of atmospheric aerosol in terms of dry mass. They play a key role in climate and climate change, so the study of their emission processes is of utmost importance. Measurements of dust emission into the atmosphere are scarce, so that the dust load is generally estimated using models. It is known that the emission process can generate strong atmospheric electric fields. Starting from the data we acquired in the Sahara desert, here, we show for the first time that depending on the relative humidity conditions, electric fields contribute to increase up to a factor of 10 the amount of particles emitted into the atmosphere. This means that electrical forces and humidity are critical quantities in the dust emission process and should be taken into account in climate and circulation models to obtain more realistic estimations of the dust load in the atmosphere.

The wavefront sensor in active and adaptive telescopes is usually not in the optical path toward the scientific detector. It may generate additional wavefront aberrations, which have to be separated from the errors due to the telescope optics. The aberrations that are not rotationally symmetric can be disentangled from the telescope aberrations by a series of measurements taken in the center of the field, with the wavefront sensor at different orientation angles with respect to the focal plane. This method has been applied at the VLT Survey Telescope on the ESO Paranal observatory.

The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The 2.6 m primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.