Meridian Astrometry Service


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Meridian Hall in the first half of the 19th Century
Meridian Hall in the first half of the 19th Century
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Meridian Hall in the first half of the 19th Century
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Troughton&Simms Meridian Circle
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Grubb Parsons Meridian Circle
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Carlos Ulrrico Cesco Observatory
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Automatic Meridian Circle of San Fernando
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Círculo Meridiano Automático de San Fernando
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Automatic Transit Circle
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San Fernando Automatic Meridian Circle

The origin of Meridian Astrometry at the Spanish Navy Observatory in San Fernando goes back to the first half of the nineteenth century when a telescope of transits, a mercury-compensated pendulum clock (1829) and a mural circle (1834) from the English instrument maker Thomas Jones, were received. The first meridian observations were conducted with the telescope of transits in 1833.

Subsequently, a new meridian circle was ordered from the English firm Troughton & Simms and was received in San Fernando at the end of 1859 and installed in the East Meridian Circle Room of the Observatory. This modern (for its time) instrument began its observations in 1863 and it kept working until the first third of the twentieth century.

What we might call modern Astrometry began at the R.O.A. in 1948, when another meridian circle was received from the English firm Grubb & Parsons which continued to be used for observing in San Fernando until the end of 1987. During this period, the Spanish Navy Observatory took part in the formation of the SRS and NPZT, international catalogues sponsored by the International Astronomical Union (IAU), and in the formation of two radio-star catalogues.

Between 1987 and 1995 a complete modernization and automation was carried out in a similar way of one of the Carlsberg Automatic Meridian Circles (CAMC). Since then, this meridian circle has been known as the Automatic Meridian Circle of San Fernando (CMASF). In May, 1996, it was moved to Argentina and settled in the Carlos Ulrrico Cesco Observatory in the province of San Juan, which belongs to the Observatorio Astronómico Félix Aguilar (OAFA) of the Universidad Nacional de San Juan, where it is currently operating at full performance. The observations are carried out by OAFA astronomers under the supervision of the R.O.A. personnel in the frame of a cooperation agreement signed between these two Institutions.

In the spring of 2001 the results of the observations carried out up to December 1999 by using a photoelectric mobile-slit micrometer were published on CD-Rom as the first Hispano-Argentino Meridian Catalogue (HAMC).

In December, 1999 a new ORBIS CCD camera equipped with a Kodak 1600 sensor (1500 x 1024 pixels, 9 microns) was mounted to conduct observations of stars in Drift Scan mode. With this camera, a new observation program was developed to observe all stars up to magnitude 16 and between declinations of -30° and 0°. This ended with the publication, in late 2008, of the Second HAMC catalogue that can be obtained (for free) by e-mail to ppmu at

At the end of the development of HAMC2 Catalogue, a second CMASF modernization is carried out with the installation of a new Finger Lakes Instrumentation CCD camera equipped with a Kodak PL6303E sensor (3072 x 2048 pixels, 9 microns), fitted with a band pass filter centred in 630 nm (Sloan r'), that has improved the precision of the observations and also its magnitude range up to 17.

In 1983, in virtue of the international convention that rules the installation of instruments in the Roque de los Muchachos Observatory, the Carlsberg Automatic Meridian Circle (CAMC) was installed by the University of Copenhagen (CUO) and the Royal Greenwich Observatory (RGO). This instrument is a completely automatized meridian circle (a twin of the CMASF) that was equipped with a photoelectric-slit micrometer. One fourth of the observation time of this telescope, available to Spain as agreed in the installation agreement, was offered to the ROA by the Instituto de Astrofisica de Canarias (IAC). Since that moment, the R.O.A. took part with the CUO and RGO in the CAMC observations that ended with the publication of a series of 11 catalogues, called "Carlsberg Meridian Catalogue, La Palma", with more than 180,000 star positions and magnitudes between declinations -40 º and 90 º and over 25,000 positions and magnitudes of planets, satellites and asteroids.

Since mid-1997 CAMC is able to be operated remotely via Internet. In June 1998, the photoelectric micrometer was replaced by an ORBIS CCD camera fitted with a Kodak 1600 sensor of 1532 x 1024 pixels and 9 microns, which was used to carry out observations of stars in Drift Scan mode. In April 1999 a new CCD camera of 2048 x 2048 pixels of 9 microns and fitted with a band pass filter centred at 630 nm (Sloan r ') was installed and has been operating to develop an program of observations to determine the positions of stars up to magnitude 17 of the celestial band between declinations -40 and +50 º.
In January 2002, a preview of the star catalogue, called CMC12, was published with the observations within the area from declinations from -3° to +3°, which was later extended to declinations from -3° to +30° in the CMC13, published in April 2003. In 2005, once the appropriate observation area was completed, a third version of this catalogue (called CMC14) was issued within an area of declination from -30º to +50º with more than 95 million stars with magnitudes between 9 and 17. These data is available via CD-ROM and can be obtained for free by e-mail to ppmu at Additionally, you can access them through the Virtual Observatory services.

In September 2004, the ROA took in charge the whole observation time and the responsibility of the telescope maintenance, along with its scientific exploitation. Thereafter, the CAMC was renamed as Automatic Transit Circle (CTA). The CMC15 Catalogue is currently in the process of observation, reduction and publication, expected to be published by the end of 2012.

CMASF features:
Type: refractor telescope
Focal length2664 mm
Aperture176 mm
Declination circle:
Diameter724 mm
Thickness9 mm
Angle between scales5'
Reading system6 cámaras CCD
Detector: CCD camera
CCD sensorKodak  KAF-6303E
Size3072 x 2048 per pixel
Pixel size9 microns
Scale0"69 píxel
Sky area covered35' declination and between 20 minutes and 1.75 hours in RA.
MagnitudeUp to magnitude 17.0 r'.
Efficiency36 million Stars per year (up to 100.000 per night).
Observatory position:
Longitude69º 19' 45" W
Latitude31º 48' 25" S
Altitude2330 m

CTA features
Type:  refractor telescope
Similar to the CMASF telescope.
Declination circle:
Similar to the CMASF telescope.
Detector: CCD camera
CCD sensorKodak  KAF-4202
Size2060 x 2048 pixel
Pixel size9 microns
Scale0"69 per pixel
Sky area covered24' declination and between 20 minutes and 2 hours in RA.
MagnitudeUp to magnitude 17.0 r'.
Efficiency30 million Stars per year (85,000 per night).
Observatory position:
Longitude17º 53' 7".8 W
Latitude28º  45' 52".4 N
Altitude2327.0 m

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