The Observatorio Astronómico Nacional at San Pedro Mártir is located at 31°02'40''N and 115°28'00''W on the summit of the Sierra San Pedro Mártir on the Baja California peninsula, Mexico, at 2800 m above sea level. The results of more than three decades of site characterization work are summarized. These cover the following aspects: weather, cloud

The site selection for the future European Large Telescope (E-ELT) is a key issue within the European proposal funded by the European Union (EU), within the ``ELT design study'' proposal. The organization, working scheme and baseline frameworks are reviewed. For the definition of the working package WP12000 ``Site Characterization'', important use

A Survey of Ensemble Physical Properties of Cometary Nuclei (SEPPCoN) is underway to characterize the nuclei of 100 Jupiter-family comets (JFC). The survey combines both visible and mid-infrared observations to measure the JFC size and albedo distributions. We inspected Spitzer Space Telescope MIPS and IRS images of the survey targets for dust

Unlike the trial procedures, a reliable characterization of the vertical turbulence distribution on a site should be based in unbiased statistical sample criteria. The sample size is as important as the criteria under which it is taken. We present here the statistical results of the optical turbulence profiles at the Roque de los Muchachos

Last year (Campins et al. 2006), we reported near-infrared rotational variability in ground-based spectra of comet-asteroid transition object 944 Hidalgo. Since then, we carried out a rotationally resolved study of Hidalgo at mid-infrared wavelengths using the Infrared Spectrograph (IRS) on NASA's Spitzer Space Telescope. We obtained 7 to 38 micron

During the last years a mayor effort has been carried out both, in defining key parameters to quantify the quality of a site for astronomical observations, and to design reliable techniques and tools to compare different sites. Here, we will revise some of the parameters relevant for astronomical site evaluation, and we will also brief on the