5751 Zao,
provisional designation , is an
Amor asteroid
The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor . The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orbit ...
discovered by Japanese astronomer
M. Koishikawa at the
Ayashi Station of the
Sendai Astronomical Observatory on 5 January 1992
Physical properties
''Zao'' has been observed by several groups to determine its rotational period. Its
light curve
In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...
was observed by
Pravec, et al. between 1992 and 1995 with the intention of determining its rotational period. From its nearly constant brightness it was determined that the asteroid is roughly spherical and has a rotational period of ≥ 21.7
hr.
Another group led by Wisniewski conducted an approximately 5 hour observation and were unable to conclude a rotational period.
''Zao'' was again observed in 2001 by
Delbó, et al. using the
Keck telescope
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and, when c ...
. They were able to determine the asteroid's
albedo
Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...
of 0.36 and re-classify the asteroid from
X-type to
E-type.
Using the asteroid's albedo and the
Near Earth Asteroid Thermal Model (NEATM) the asteroid's
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
was estimated to be 2.3 km.
[ Further study of the asteroid by the Ondrejov Asteroid Photometry Project concludes that a rotational period of 76 hours is consistent with earlier measurements.]
References
External links
IAUC 5426 – Initial discovery
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{{DEFAULTSORT:Zao
005751
Discoveries by Masahiro Koishikawa
Named minor planets
005751
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