National Institute for Astrophysics
The Northern Cross is, currently, composed of two perpendicular arms that are 564 m long (East-West) and 640 m long (North-South) and it has a useable total surface area of 30000 m2. Thanks to this vast area the antenna is capable of detecting very weak radio sources. The antenna observes "through" a 2.7 MHz wide window, centered at 408 MHz and it has been mainly used to effect high sensitivity sky surveys and, thus, to produce large radio-source catalogues, which have been and are still today of fundamental importance for astronomical research. Furthermore the "Cross" has been used for pulsars research and for the spectrometric study of interstellar dust (emission line of ionized hydrogen and of ionized carbon). Currently the instrument is being converted and upgraded in order to meet the international SKA (Square Kilometre Array) program requirements. The ultimate goal ia a next generation radiotelescope with a useable total surface area of 1 km2 area. The "Cross", in fact, represents an ideal test ground for SKA technologies and data acquisition systems. The 32 m parabolic antenna is employed both for single dish observations and for interferometry. In interferometry it works together with the other EVN (European Very Long Baseline Interferometry Network) antennas, installed all over Europe, in order to produce very high resolution images, which are quite useful for detailed radio sources studies. The radiotelescope can receive radio signals within the 1.4 ÷ 23 GHz range. In single dish, it is mainly used for : H2O and methanol maser spectrometry, monitoring of extragalactic compact sources flux variability, galactic polarimetric surveys, studies of comets, extrasolar planet research, and radar monitoring of Near Earth Objects (in collaboration with the NASA) The astronomical interferometric observations are, also, used for geodynamic studies. The VLBI techniques, in fact, allow measurement of the distance between the various antennas with a millimetric degree of accuracy. It is therefore the most precise way of monitoring and studying the movements of the Earth's crust.