Facility overview and optical layout

The six CHARA telescopes are arranged in a Y-shape configuration providing 15 baselines ranging from 34 - 331 meters in length and up to 10 possible closure phase measurements. A majority of the infrastructure at CHARA consists of telescopes, vacuum light beam transport tubes, optical path length delay lines, beam management systems, and beam combination systems. The optical layout of many of these elements is presented in the figure below:

For further discussion of the facility, please see the publication First Results from the CHARA Array. II. A Description of the Instrument (pdf).


Each of the six telescopes is a 1 m Mersenne-type afocal beam reducer that injects a 12.5 cm output beam into the vacuum transport tubes. The telescopes are enclosed in 16.5 ft domes which open up for optimal airflow (see below).

Baselines and configurations

The six CHARA telescopes provide 15 baselines ranging from 34 - 331 m in length:

Baseline Length (m) Position Angle
W2-S1 210.97 340.88
W2-S2 177.45 339.08
W2-E1 221.82 241.27
W2-E2 156.27 243.23
W2-W1 107.92 99.11
W1-S1 278.50 321.02
W1-S2 249.39 317.18
W1-E1 313.53 253.39
W1-E2 251.34 257.73
E2-S1 278.76 14.63
E2-S2 248.13 17.87
E2-E1 65.88 236.60
E1-S1 330.66 22.28
E1-S2 302.33 25.70
S2-S1 34.07 350.29

Normally a two telescope combiner can be used with any two telescopes (one baseline), a 3-telescope combiner with any 3 telescopes (3 baselines), etc. The selection of telescopes can be changed during the night, within some limitations, provided it is part of the observing request and plan - please inquire for more specific information.


Presently the array does not have any offset tracking capabilities. All targets must satisfy all requrements for acquisition, tip/tilt tracking, and beam combiner limiting mangitudes.