An Etymological Dictionary of Astronomy and Astrophysics

A huge theoretical cloud of → comets surrounding the Sun between about 50,000 and 100,000 → astronomical units
and thought to be the reservoir of → long-period comets
entering the inner solar system.

See also: Named after Jan Hendrik Oort (1900-1992), a Dutch astronomer who proposed its existence in 1950. He also made major contributions to our knowledge of the structure and rotation of the Milky Way Galaxy; → cloud.

A huge theoretical cloud of → comets surrounding the Sun between about 50,000 and 100,000 → astronomical units
and thought to be the reservoir of → long-period comets
entering the inner solar system.

See also: Named after Jan Hendrik Oort (1900-1992), a Dutch astronomer who proposed its existence in 1950. He also made major contributions to our knowledge of the structure and rotation of the Milky Way Galaxy; → cloud.

1. The upper limit for the density of all matter in the plane of the Galaxy near the Sun’s
   locality, as calculated from the velocities and distribution of stars in relation to the gravitational field of the Galactic disk. The value is 0.14 solar masses per cubic parsec, or 9.5 x 10^-24 g cm³.
   

2. The outer boundary of the → Oort cloud. The current estimate is about 100,000 → astronomical units from the Sun, which is approximately one third of the distance to the nearest star → Alpha Centauri.

See also: → Oort cloud; → limit.

1. The upper limit for the density of all matter in the plane of the Galaxy near the Sun’s
   locality, as calculated from the velocities and distribution of stars in relation to the gravitational field of the Galactic disk. The value is 0.14 solar masses per cubic parsec, or 9.5 x 10^-24 g cm³.
   

2. The outer boundary of the → Oort cloud. The current estimate is about 100,000 → astronomical units from the Sun, which is approximately one third of the distance to the nearest star → Alpha Centauri.

See also: → Oort cloud; → limit.

A 40-year period of unusually low → solar activity, from about 1010 to 1050. See also the → Maunder minimum.

See also: → Oort cloud; → minimum.

A 40-year period of unusually low → solar activity, from about 1010 to 1050. See also the → Maunder minimum.

See also: → Oort cloud; → minimum.

Two parameters, denoted A and B, that describe the major features of our Galaxy’s differential rotation in the Sun’s neighbourhood. A is one-half of the shear and equal to +14.4 ± 1.2 km s^-1 kpc^-1, and B, one-half of the vorticity, equal to -12.0 ± 2.8 km s^-1 pc^-1.

See also: → Oort cloud; → constant.

Two parameters, denoted A and B, that describe the major features of our Galaxy’s differential rotation in the Sun’s neighbourhood. A is one-half of the shear and equal to +14.4 ± 1.2 km s^-1 kpc^-1, and B, one-half of the vorticity, equal to -12.0 ± 2.8 km s^-1 pc^-1.

See also: → Oort cloud; → constant.