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

The primary color between green and orange in the visible spectrum; an effect of light with a wavelength between 5700 and 5900 Å. → yellow giant; → yellow supergiant.

M.E. yelou; O.E. geolo, geolu; P.Gmc. *gelwaz (cf. O.S., O.H.G. gelo, M.Du. ghele, Du. geel, Ger. gelb, Swed. gul "yellow"); cognate with Pers. zar "yellow," as below.

Zard "yellow," related to zarr "gold;" Mid.Pers. zard "yellow," zarr "gold;" O.Pers. daraniya- "gold;" Av. zaray-, zairi- "yellow, green," zaranya-, zarənu- "gold;" cf. Skt. hari- "yellow, green," hiranya- "gold;" Gk. chloros "light green," chloe "green shoot;" L. helvus "yellowish, bay;" Rus. zeltyj "yellow;" P.Gmc. *gelwaz, as above.

A star that appears in the upper-middle part of the → H-R diagram, to the left of the → red giants. Yellow giants are low-mass evolved stars that are burning their helium, on their path to the → planetary nebula stage. Most yellow giants behave as variable stars, usually because their outer layers pulsate. Periods of these pulsations are usually days or weeks. The Sun after leaving the red giant stage will become a pulsating yellow giant for some 100 million years.

→ yellow; → giant.

An evolved, → very massive star of spectral type F or G with a very high luminosity (~10⁵ times solar) lying near the empirical upper luminosity boundary in the → H-R diagram (→ Humphreys-Davidson limit). Yellow hypergiants have high → mass loss rates (10^-5-10^-3 solar masses per year) and are in a short, transitional evolutionary stage. Their evolutionary state is thought to correspond to post-red supergiants rapidly evolving in blueward loops in the H-R diagram. In their post-RSG blueward evolution these stars enter a temperature range (6000-9000 K), called → yellow void, with increased dynamical instability. Their link to other advanced evolutionary phases of massive stars such as → Luminous Blue Variables and → Wolf-Rayet stars is still an open issue in stellar evolution theory. The most famous yellow hypergiant is → Rho Cassiopeiae.

→ yellow; → hypergiant.

A supergiant star of type F and G whose effective temperature is between 4800 and 7500 K. Yellow supergiants are extremely rare, because they represent a very short-lived phase, typically a few tens of thousands of year, in the evolution of → massive stars.

→ yellow; → supergiant.

A temperature range (6000-9000 K) in the → H-R diagram occupied by → yellow hypergiants in their post-RSG blueward evolution, where high → mass loss episodes occur.

→ yellow; → void.

The final product obtained from the processing of uranium ores. It is a coarse powder, a mixture of uranium oxides, with about 80% U₃O₈. It has a pungent odor and melts at approximately 2878 °C. The yellowcake produced by most modern mills is actually brown or black, not yellow; the name comes from the color of the concentrates produced by early mining operations due to impurities from ammonium diuranate. Yellowcake must be converted into → uranium hexafluoride (UF₆) before it can be enriched, the process that makes the sort of uranium used by nuclear power plants or bomb-makers (→ uranium enrichment). The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.

→ yellow; cake, M.E., from O.Norse kaka "cake," from which also derive M.Du. koke, Du. koek, Ger. Kuchen.