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{{#invoke:Infobox|infobox}} 127 Johanna is a large, dark main-belt asteroid that was discovered by French astronomers Paul Henry and Prosper Henry on November 5, 1872, and is believed to be named after Joan of Arc.<ref name=schmadel2003/> It is classified as a CX-type asteroid, indicating the spectrum shows properties of both a carbonaceous C-type asteroid and a metallic X-type asteroid.<ref name="icarus186_1_126"/>

A photoelectric study was performed of this minor planet in 1991 at the Konkoly Observatory in Hungary. The resulting light curve showed a synodic rotation period of 6.94 ± 0.29 hours with a brightness variation of 0.2 in magnitude. It was estimated to have an absolute magnitude of 8.459 ± 0.013 with a diameter of 96–118 km and an albedo of 0.06–0.04.<ref name="Toth1997"/>

Infrared observations made in 1982 at Konkoly showed a rapid variation that seemed to suggest a shorter rotation period of 1.5 hours; one of the fastest known at the time. However, an irregular shape was suggested as an alternative cause of the rapid variation.<ref name="Szecsenyi-Nagy1983"/> The present day established rotation period of this object is 12.7988 hours.<ref name="Behrend"/>

During 2001, 127 Johanna was observed by radar from the Arecibo Observatory. The return signal matched an effective diameter of 117 ± 21 km.<ref name="icarus186_1_126"/> A larger diameter value of 123.41 ± 4.07 km was obtained from the Midcourse Space Experiment observations, with an albedo of 0.0557 ± 0.0039.<ref name="Tedesco2002"/> A 2012 study gave a refined diameter estimate of 116.14 ± 3.93 km.<ref name="Carry2012"/>


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