An Etymological Dictionary of Astronomy and Astrophysics

A very familiar antenna array, which is the commonest kind of terrestrial TV aerial to be found on the rooftops of houses.
It consists of a single “feed” or “driven element,” usually a dipole antenna. The rest of the elements help transmit the energy in a particular direction. These antennas typically operate in the HF to UHF bands (about 3 MHz to 3 GHz), although their bandwidth is typically small. In astronomy Yagi antennas are used as elements in some → radio interferometers. Same as Yagi-Uda antenna.

See also: Named after the Japanese electrical engineer Hidetsuga Yagi (1886-1976); → antenna.

A very familiar antenna array, which is the commonest kind of terrestrial TV aerial to be found on the rooftops of houses.
It consists of a single “feed” or “driven element,” usually a dipole antenna. The rest of the elements help transmit the energy in a particular direction. These antennas typically operate in the HF to UHF bands (about 3 MHz to 3 GHz), although their bandwidth is typically small. In astronomy Yagi antennas are used as elements in some → radio interferometers. Same as Yagi-Uda antenna.

See also: Named after the Japanese electrical engineer Hidetsuga Yagi (1886-1976); → antenna.

The largest → impact crater on → Ceres after → Kerwan. It is adjacent to another large crater, called → Urvara. Yalode appears to have a series of canyons running from it, in a northwestern direction.

See also: Named after Yalodé, the West African (Dahomeyan) deity of harvest.

The largest → impact crater on → Ceres after → Kerwan. It is adjacent to another large crater, called → Urvara. Yalode appears to have a series of canyons running from it, in a northwestern direction.

See also: Named after Yalodé, the West African (Dahomeyan) deity of harvest.

A phenomenon that causes a slow variation of the orbital elements of asteroids and meteoroids. It takes place because the surface thermal conductivity of these bodies is not negligible and the rotation of the body about its axis shifts the warmest region from midday to the object’s afternoon hemisphere. Consequently the temperature distribution is asymmetric with respect to the Sun direction, and the momentum carried off by the photons emitted in the infrared has a net component along the orbital velocity of the asteroid. This causes a decrease or increase of its orbital energy depending on whether the rotation is prograde or retrograde. The bodies therefore spiral either sunward or outward. The secular drift of the semi-major axis of the orbit is estimated to be of the order of 10^-4 A.U. per million years for a → near-Earth object with a diameter of 1 km. The effect is unimportant for bodies larger than a few km because of their very large mass per unit area (10⁶ g cm^-2 or more) and is especially unimportant for comets that spend little time under intense illumination close to the Sun. Compare with the → Poynting-Robertson effect, which is isotropic.
See also → YORP effect.

See also: Named after Ivan Osipovich Yarkovsky (1844-1902), a Russian-Polish civil engineer. Yarkovsky knew nothing of photons and based his reasoning on the → ether concept, but his idea survives the translation to modern physics; → effect.

A phenomenon that causes a slow variation of the orbital elements of asteroids and meteoroids. It takes place because the surface thermal conductivity of these bodies is not negligible and the rotation of the body about its axis shifts the warmest region from midday to the object’s afternoon hemisphere. Consequently the temperature distribution is asymmetric with respect to the Sun direction, and the momentum carried off by the photons emitted in the infrared has a net component along the orbital velocity of the asteroid. This causes a decrease or increase of its orbital energy depending on whether the rotation is prograde or retrograde. The bodies therefore spiral either sunward or outward. The secular drift of the semi-major axis of the orbit is estimated to be of the order of 10^-4 A.U. per million years for a → near-Earth object with a diameter of 1 km. The effect is unimportant for bodies larger than a few km because of their very large mass per unit area (10⁶ g cm^-2 or more) and is especially unimportant for comets that spend little time under intense illumination close to the Sun. Compare with the → Poynting-Robertson effect, which is isotropic.
See also → YORP effect.

See also: Named after Ivan Osipovich Yarkovsky (1844-1902), a Russian-Polish civil engineer. Yarkovsky knew nothing of photons and based his reasoning on the → ether concept, but his idea survives the translation to modern physics; → effect.

A crater about 70 km in diameter in Western Australia, considered to be the oldest recognized → meteorite impact structure on Earth. A precise age of 2 229 ± 5 million years is derived from shocked zircon and monazite crystals in the rocks. The age coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits. Numerical impact simulations indicate that a 70 km size crater created by the impact in a continental glacier could release between 8.7 × 10¹³ to 5.0 × 10¹⁵ kg of H₂O vapor instantaneously into the atmosphere. These results provide new estimates of impact-produced H₂O vapor abundances for models investigating termination of the Paleoproterozoic glaciations, and highlight the possible role of impact cratering in modifying Earth’s → climate (Erikson, T.M. et al., 2020, Nature communications, 21 January).

See also: The Yarrabubba structure is located on the Yilgarn Craton in Western Australia (lat. 27° 11’S, long. 118° 50’E), approximately 100 km southeast of the township of Meekatharra; → crater.

A crater about 70 km in diameter in Western Australia, considered to be the oldest recognized → meteorite impact structure on Earth. A precise age of 2 229 ± 5 million years is derived from shocked zircon and monazite crystals in the rocks. The age coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits. Numerical impact simulations indicate that a 70 km size crater created by the impact in a continental glacier could release between 8.7 × 10¹³ to 5.0 × 10¹⁵ kg of H₂O vapor instantaneously into the atmosphere. These results provide new estimates of impact-produced H₂O vapor abundances for models investigating termination of the Paleoproterozoic glaciations, and highlight the possible role of impact cratering in modifying Earth’s → climate (Erikson, T.M. et al., 2020, Nature communications, 21 January).

See also: The Yarrabubba structure is located on the Yilgarn Craton in Western Australia (lat. 27° 11’S, long. 118° 50’E), approximately 100 km southeast of the township of Meekatharra; → crater.