An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A phenomenon in which the rotation rate of a small asteroid changes under sunlight absorption. Photons from the Sun are absorbed by a small body and reradiated in infrared. In the process, two forces influence the object: one from the impact of the photons, providing a tiny push, and the other as a recoil effect when the object emits the absorbed energy. In the YORP effect the body's shape has a more effective role than albedo in altering the spin rate. For small asteroids (< 10 km), YORP can cause measurable changes in rotation rate. The effect can even speed up the rotation leading to disintegration. → Yarkovsky effect.

Short for Ivan Osipovich Yarkovsky, John A. O'Keefe, V. V. Radzievskii, and Stephen J. Paddockk, who developed the explanation; → effect.

A metric prefix denoting 10²⁴.

On the model of → yocto-.

Being in the first or early stage of existence or evolution; e.g. → young stellar object.

M.E.; O.E. geong "youthful, young," from P.Gmc. *jungas (cf. O.S., O.Fris. jung, O.N. ungr, M.Du. jonc, Du. jong, O.H.G., Ger. jung, Goth. juggs), from PIE base *yeu- "vital force, youthful vigor;" cognate with Pers. javân, as below.

Javân "young;" Mid.Pers. juwân "young, youth;" Arm. yavanak (loaned from Mid.Pers.); Av. yuuan- "youth;" cf. Skt. yuvan- "young, youth;" L. juvenis "young man;" Lith. jaunas "young;" O.C.S. junu, Rus. junyj "young;" cognate with E. young, as above.

Any star that has evolved past the → protostar stage, but has not yet arrived on the → main sequence. There is a variety of YSOs depending on their age, mass, and environment, including → Herbig stars, → T Tauri stars, and, in general, compact infrared sources embedded in molecular clouds.

→ young; → stellar; → object.

A method of producing → interference of light. Two beams of → coherent light are produced by passing light through a very small circular aperture in one screen, then through two small circular apertures very close together in a second screen. On a third screen, behind the second screen, there will be two overlapping sets of waves and, if the light is monochromatic, → interference fringes will appear on the third screen. The experiment can also be performed with a beam of electrons or atoms, showing similar interference patterns. Young's experiment provides an evidence of the → wave-particle duality, as explained by → quantum mechanics. Same as → double-slit experiment.

Named after the English scientist Thomas Young (1773-1829), who originally performed the experiment some time around 1801 in an attempt to resolve the question of whether light was composed of particles (the → corpuscular theory of light); or rather consisted of waves travelling through some → ether. The experiment proved the wave nature of light; → experiment.

A measure of elasticity of a material, defined as the ratio of tensile → stress to tensile → strain, which equals the ratio of compressive stress to compressive strain.

Named after Thomas Young, → Young's experiment.

Same as → paradox of youth.

A soft, malleable, silver-white metallic chemical element; symbol Yb. Atomic number 70; atomic weight 173.04; melting point 819°C; boiling point about 1,194°C; specific gravity about 7.0. It has several radioactive isotopes.

From Ytterby, the name of the Swedish village where the mineral ytterbite (the source of ytterbium) was originally found. It was discovered by the Swiss chemist Jean-Charles Galissard de Marignac in 1878.

A highly crystalline iron-gray metallic chemical element; symbol Y. Atomic number 39; atomic weight 88.9059; melting point about 1,522°C; boiling point 3,338°C; specific gravity about 4.45. It has several radioactive isotopes.

From ytterbite, → ytterbium, which turnd out to be containing two different elements.

The potential function that is associated with the strong, short-ranged force resulting from the exchange of massive particles between two → nucleons in the same atomic nucleus. The potential has the form of V(r) = C. (1/r) exp (-K.r), where r is the distance between the nucleons and C and K are constants, giving measures of the strength and range of the force respectively.

In honor of the Japanese physicist Hideki Yukawa (1907-1981), winner of the 1949 Nobel Prize in Physics; → potential.