The COATLI telescope is an ASTELCO Systems 50-cm f/8 Ritchey-Crétien reflector with protected aluminum coatings.


The telescope is located at the Observatorio Astronómico Nacional in the Sierra de San Pedro Mártir in Baja California, México, at 31°02’42.2” N 115°27’57.4” W and at an altitude of 2800 meters.


The telescope is installed on a concrete and steel tower on a rocky outcrop. The telescope axes are about 6.2 meters above rocks and the rocks are a similar height above the ground.


The telescope is protected by an ASTELCO Systems ARTS folding enclosure.


The telescope mount is an ASTELCO Systems NTM-500.

The telescope is mounted in a German equatorial configuration. Thus, to move from one side of the meridian to the other, it needs to do a “meridian flip”: move first in declination to the pole and then move in HA to the other side.

One consequence of this is that the instrument rotates by 180 degrees with respect to the sky as it moves from east to west. The mount rotation is given by the SMTMRO and EMTMRO keywords in the FITS headers of images.

The mount is fast; when slewing it accelerates at 10 deg/s2 to a velocity of 30 deg/s. Thus, the slew time typically less than 10 seconds between two points on the same side of the meridian but typically 20-30 seconds between two points on different sides of the meridian (because of the need to do a meridian flip).

The high slew speed gives COATLI two advantages compared to conventional telescopes. One is that it can quickly respond to transient events such as GRBs. The other is that it can rapidly move between many objects, for example, to observe standard stars or to monitor galaxies for transients.

Pointing Limits

The telescope can point over the whole sky (including under the pole) to a zenith distance of 85 degrees.


The telescope and mount have two major problems that severely impact image quality.