boundary of the composite carbon monoxide survey of Dame et al. (2001). As of June 2013 this survey is nearly complete, consisting of over 375,000 spectra and covering ~24,000 sq-deg with 1/4° sampling. In addition, all molecular clouds at |b| > 10° and dec > −15° (~248) have been mapped every beamwidth. In 2011, Dame and Thaddeus found clear evidence in existing 21 cm surveys for a large extension of the Scutum-Centaurus Arm, one of the two major spiral arms thought to extend from the ends of the galactic bar. The "Outer Sct-Cen arm" lies well beyond the solar orbit on the far side of the galaxy, roughly 21 kpc from the Sun. The CfA 1.2 m telescope has so far detected 22 distinct giant molecular clouds associated with HI peaks in the arm, and a large, unbiased carbon monoxide survey of the entire arm was begun in the fall of 2013; it is expected to require ~2 years to complete. Technical information Antenna The antenna system consists of a 1.2 m parabolic primary and 17.8 cm hyperbolic secondary in a Cassegrain configuration with effective f/D=2.8. The antenna primary is a monolithic aluminum casting with f/D=0.375, numerically milled by Philco Ford to 40 µm surface accuracy (l/65 at 115 GHz). The telescope's focus, beam pattern, and main beamwidth were most recently measured and adjusted in the fall of 1994 using a transmitter in the intermediate field (1.4 km distant on the roof of Harvard's William James Hall). The beam pattern matches well the predictions of scalar diffraction theory. The beamwidth (FWHM) is 8.4+/-0.2 arcmin and the main beam efficiency 82%. The antenna is housed in a 16 ft Ash dome with a 75 in slit. During normal observations, the slit is covered with a screen of woven PTFE (polytetrafluoroethylene—Teflon), selected for its near transparency to microwaves, its strength, and its resistance to aging. The screen keeps the wind out of the dome and makes possible regulation of the temperature inside. LO reflections from the PTFE screen were found to be the source of occasional standing waves in scan baselines; subsequent modification of the mounting plates at the bottom and top of the screen gave it a "V" shape, eliminating surfaces of constant phase for the reflected LO and solving the standing wave problem. Mount and drive The telescope mount and drive systems are essentially unchanged from their configurations at Columbia.