The Automatic Transit Circle (ATC) is an old meridian circle built by Grubb-Parsons in 1950 but completely refurbished and automatized in the 70's of the past century by the Copenhagen University Observatory (CUO). It main task is to observe evenly bodies at their transit across the meridian. At present it is installed in the Roque de los Muchachos Observatory (ORM) at 18º W of longitude, 29º N of latitude and 2227 m of altitude. The instrument observes robotically without any observer in charge. Only need a daily remote maintenance and authorization to observe (green light) from the observer. Twice a year are performed mechanical and electronic maintenance by specialist personnel travelling to the ORM.
Since 1950 was operated by his owner, the CUO, in the Brorfelde observatory (Denmark). In 1983 after the automation was moved to the ORM in La Palma island (Canary Islands, Spain). Since 1984 is observing continuously in that place operated jointly by the CUO from Denmark, the Royal Greenwich Observatory (RGO) from UK and the Real Instituto y Observatorio de la Armada (ROA) for Spain. Until 1999 it was provided of a photoelectrical micrometer. Until 1997 the instrument was operated by observer in site and since then remotely and automatically via internet. In 1999 the photoelectric micrometer was replaced by a CCD camera operating in drift scan mode and since then it is observing a survey of stars brighter than 17 R' between -30º to +50º. After the closing down of the RGO and until April of 2001 de Institute of Astronomy of Cambridge (IoA) was in charge of the British compromise in the project. Still and until the end of the survey the IoA participate in the necessary computes for the survey publication.
At the end of 2004 the CUO have also abandoned the project doing cession of the ATC to the IAC. This institution have left the usufruct of the instrument to the ROA, any way the CUO and IoA will participate in the publication of the final survey. The ROA will be in charge of the remote operations of the ATC, participating also in the reductions of the observations.
The ATC have an useful aperture of 176 mm and a focal length of 2664 mm. The declination circle is in glass with an outer diameter of 732 mm and graduated every 5'. The position of the circle is read by six CCD cameras with a precision of a few of tenths of arsec.
The setting process is carried out in two step: in the first one two motor moving a big gear wheel set the instrument with an error less than 2 arcmin of the required position. Then a stepping motor in combination with the circle reading system set the instrument in it final setting with an error of about 2 arcsec. The total process take less than 45 seconds.
The robotic system is managed by two PC's and the circle reading is performed by a microprocessor based device designed and built in the CUO electronic workshop. One of the PC the Telescope Process Controller (TCC) is in charge of all the automated process: setting of the instrument, opening and closing of the dome, managing of the CCD camera and checking if the weather conditions allow the observation.
At present it is provided with a CCD camera with 2048x2048 squares pixels of 9 microns observing in drift scan mode. Observing in this mode the instrument is able to observe sky stripes parallel to the equator 0f 24' in declinations and between 20 minutes and 5 hours in right ascension.
With the observations carried out in La Palma with the photoelectrical micrometer was published the serie of catalogues CMC, La Palma, nº 1 to 11, these catalogues contain right ascension, declinations, proper motions and magnitude for stars brighter than 16 V and declinations between -40º and +90º, also positions and magnitudes for selected solar system objects. Catalogues CMC 1 to 8 were published in printed format. CMC9 and CMC1-11 where published in CD-ROM.
After the installation of the CCD camera have been made publish in the Web the catalogues CMC12 with more than 9000000 of positions and magnitudes of stars brighter than 17 R' and declination between -3º and +3º and CMC13 (superseding CMC12) with almost 40000000 stars with declinations between -3º y +30º.
Late 2005 or early 2006 will be made publish in the Web the CMC14 (this catalogue will supersede to CMC12 and CMC13) with start between -30º and +50º. Meanwhile the instruments continue making the necessary observations to complete the catalogue.
The futue plans for the instrument are to continue the observations with a new band between -30º and -40º and in parallel to observe selected Solar System objects and zones of the Sky with special astrophysical interest.