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

The broad continuum feature dominating the optical-ultraviolet spectra of AGNs. Most current models attribute the big blue bump to thermal emission from an optically thick accretion disk.

→ big; → blue; bump, → bump Cepheid.

The hue of that portion of the visible spectrum lying between green and indigo, evoked in the human observer by radiant energy with wavelengths of approximately 420 to 490 nanometers.

From O.Fr. bleu, P.Gmc. *blæwaz, from PIE base *bhle-was "light-colored, blue, blond, yellow."

Âbi "color of water," from âb "water," Mid.Pers. âb, O.Pers./Av. âp-, Skt. âp-, PIE *âp-; → Aquarius.

An small → irregular galaxy undergoing → violent star formation activity. These objects appear blue by reason of containing clusters of hot, → massive stars which ionize the surrounding interstellar gas. They are chemically unevolved since their → metallicity is only 1/3 to 1/30 of the solar value. Same as → H II galaxy.

→ blue; → compact; → dwarf; → galaxy.

The → continuum emission of an astronomical source with wavelengths between about 492 and 455 nm.

→ blue; → continuum.

A giant star with spectral type O or B.

→ blue; → giant.

Qul, → giant; âbi, → blue.

A star belonging to a variety of stars located above the → horizontal branch and blueward of the → red giant branch in the → Hertzsprung-Russell diagram of the → halo population.

→ blue; → halo; → star.

Setâregân plural of setâré, → star, âbi, → blue, hâlé, → halo.

Same as → blue horizontal branch star.

→ blue; → horizontal; → branch; → star.

A rare class of → horizontal branch (HB) stars that so far have been found in only very few Galactic → globular clusters. These stars are such called because they form a blue hook at the hot end of the HB in → far ultraviolet (FUV) → color-magnitude diagrams. The physical mechanism that produces blue hook populations is still uncertain. At least two scenarios have been proposed.
In the first scenario these stars are explained as a consequence of extreme → mass loss during the → red giant branch phase and late helium flashing while descending the → white dwarf cooling track. Due to the thin residual hydrogen envelope, helium is mixed into the envelope and hydrogen is mixed into the core during the late → helium flash. As a result, the stars are hotter and UV-fainter than canonical → extreme horizontal branch stars (EHB).
By contrast, in the He self-enrichment scenario the EHB and blue hook stars are produced via the normal evolution of He-enriched sub-populations in globular clusters. These sub-populations might have formed from the ejecta of intermediate-mass → asymptotic giant branch (AGB) stars of the first generation of stars. For the same age and → metallicity, He-enriched HB stars have smaller masses than normal HB stars, resulting in bluer → zero age horizontal branch star (ZAHB) locations. They are also brighter in the FUV, but this effect is reversed for very hot He-enriched HB stars with → effective temperatures larger than 19000 K.
See Dieball A., et al., 2013, arXiv:0901.1309v1, and for blue hook stars in ω Cen cluster, M. Tailo et al., 2015, Nature 523, 318.

→ blue; → hook; → star.

A member of a population of blue stars appearing on the → horizontal branch in the → Hertzsprung-Russell diagram of the Galactic → halo populations and → globular clusters. Belonging to → spectral types B3 to A0, they have evolved past the → red giant stage and are burning helium in their core.

→ blue; → horizontal; → branch, → star.

A transient optical phenomenon in the → stratosphere that emerges from the tops of → thunderstorm clouds at tremendous speeds. As their name implies, blue jets are optical ejections from the top of the electrically active core regions of thunderstorms. Following their emergence, they typically propagate upward in narrow cones at vertical speeds of roughly 100 km/s, fanning out and disappearing at heights of about 40-50 km. See also → sprite; → elve.

→ blue; → jet.

Leakage phenomenon in a filter, causing an unwanted response to the blue or green light.

→ blue; leak, from M.Du. leken "to drip, to leak," or from O.N. leka, cognate of O.E. leccan "to moisten," from P.Gmc. *lek- "deficiency" (cf. O.H.G. lecchen "to become dry," Ger. lechzen "to be parched with thirst").

Našt "leak," origin unknown; âbi, → blue.

An evolutionary behavior of certain stars, particularly massive stars, which return to the blue stage after becoming a red supergiant. The phenomenon appears as a blueward loop on the theoretical evolutionary tracks.

→ blue; → loop.

Gerdâl, → loop, âbi, → blue.

The second full moon in a calendar month. For a blue moon to occur, the first of the full moons must appear at or near the beginning of the month so that the second will fall within the same month. Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month. This happens every two and a half years, on average.

The folkloric term blue Moon for the calendrical event is new, and apparently goes back to the Maine Farmers' Almanac for 1937. But its original meaning in that work was the third full Moon in a season when there were four full Moons in that season. Some have related the term to the much older English expression moon is blue, which goes back to a couplet from 1528, interpreting it as "something that occurs rarely." However in that poem the expression had a meaning of "something that was absurd." Alternatively, the term blue Moon may have been borrowed from the Chinese lunar calendar particularly in its usage among American Chinese community. In fact in that calendar when there are two full Moons in a month they use the term "blue Moon" and add a thirteenth intercalary month. → blue; → moon.

The portion of the → visible spectrum lying between 455 and 492 nm.

→ blue; → region.

A phenomenon which results from → Rayleigh scattering of sunlight by → atmospheric molecules. → Nitrogen and → oxygen molecules that compose about 78% and 21% of the air, respectively, are small compared to the light → wavelengths, and thus more effective at scattering shorter wavelengths of light (blue and violet). The → selective scattering by these → molecules is responsible for producing the blue skies on a clear sunny day. The sky over the horizon appears much paler in color, because the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Hence, less blue light reaches the observer's eyes.

→ blue; → sky.

Any of stars, often found in → globular clusters and old → open clusters, that lie on the blueward extension of the → main sequence beyond the → turnoff point. Blue stragglers have an anomalously blue color and high luminosity in comparison with other cluster members. The most probable ways in which they could form are: → mass transfer or → coalescence in → close binary systems, encounters or collisions in overcrowded cores of globular clusters.

→ blue; → straggler.

An evolved star of spectral type O, B, or A; e.g. → Rigel, → Deneb.

→ blue; → supergiant.

The → line wing with wavelengths shorter than that of the emission or absorption peak.

→ blue; → wing.

The edible, usually blueish berry of various shrubs belonging to the genus Vaccinium, of the heath family (TheFreeDictionary).

→ blue; → berry.

A galaxy having a very small size (< 1 kpc), very low stellar mass (typically 10^6.5 to 10^7.5  Msun), very low gas → metallicity (3 to 10% solar → metallicity, and very high → ionization. Blueberry galaxies, compared to star forming → dwarf galaxies, have similar stellar mass and luminosity, but much stronger → [O III] doublet (λλ4959+5007) line strength and gas ionization. Because Blueberry galaxies are selected by the strong [O III] → emission lines, they represent the star-forming → dwarf galaxies with the highest emission line strength and gas ionization. On the other hand, compared to → Green Pea galaxies at → redshifts z ~ 0.2-0.3 and typical high-z→ Lyman alpha emitting galaxies (LAEs) found in the current narrow-band surveys, Blueberry galaxies have similarly strong emission lines but about 10-100 times smaller stellar mass, → star formation rate, and luminosity. So Blueberry galaxies represent the faint-end of → Green Pea galaxies and → Lyman alpha emitting galaxies (Yang et al, 2017, arxiv/1706.02819, and references therein).

→ blueberry; → galaxy.