49777 Cappi, provisional designation 1999 XS, is a stony asteroid from the inner regions of the asteroid belt, about 1.9 kilometers in diameter. It was discovered by Italian–American astronomer Paul Comba at the U.S. Prescott Observatory in Arizona, on 2 December 1999.
The assumed S-type asteroid orbits the Sun at a distance of 2.2–2.5 AU once every 3 years and 7 months (1,321 days). Its orbit shows an eccentricity of 0.07 and is tilted by 4 degrees to the plane of the ecliptic. A photometric light-curve analysis performed at the Palomar Transient Factory in 2013, rendered a rotation period of ±0.0018 hours with a brightness amplitude of 0.78 in 5.9389magnitude. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.20, a typical value for an asteroid with a stony surface composition.
The minor planet was named after Margaret Capitola Sonntag Comba (b. 1940), a psychologist and art therapist by profession, faculty member at Prescott College, and wife of the discoverer.
The constant altitude plan position indicator, better known as CAPPI, is a radar display which gives a horizontal cross-section of data at constant altitude. It has been developed by McGill University in Montreal by the Stormy Weather Group to circumvent some problems with the PPI:
In 1954,McGill University got a new radar(CPS-9) which had a better resolution and used FASE (Fast Azimuth Slow Elevation) to program multi-angle soundings of the atmosphere.
In 1957, Langleben and Gaherty developed a scheme with FASE to keep only the data at a certain height at each angle and scan on 360 degrees. If we look at the diagram, each angle of elevation or PPI has data at height X at a certain distance from the radar. Using the data at the right distance, one forms an annular ring of data at height X. Assembling all the rings coming from the different angles gives you the CAPPI.