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

An → isophotal radius of a galaxy, where the → surface brightness in the B band falls to 25 mag arcsec^-2.

After the French-born American astronomer Gérard de Vaucouleurs (1918-1995); → radius.

1) Deprived of life.
2) No longer producing or functioning. → dead pixel.

M.E. deed, O.E. dead "dead;" cf. O.S. dod, Dan. død, Swed. död, Du. dood, O.H.G. tot, Ger. tot; PIE *dhou-toz-, from base *dheu- "to die."

Mordé "dead," p.p. of mordan, mir- "to die," → death.

Of a → CCD detector, a pixel that is not sufficiently active.

→ dead; → pixel.

The time by which something must be finished or submitted; the latest time for finishing something (Dictionary.com).

Historically, during the American Civil War, the term referred to a physical line or boundary beyond which prisoners were shot; → dead; → line.

Ruzband, literally "day lock, that which blocks date," from ruz, → day, + band, → bond; cf. Ger. Stichtag, Anmeldeschluss, Einsendeschluss and Fr. date de clôture.

1) To lower in dignity or estimation; bring into contempt.
2) To lower in character or quality; debase.
3) Chemistry: Of a compound, especially an organic hydrocarbon, to break down (Dictionary.com).

→ de-; → grade.

The electromagnetic radiation produced by an oscillating → electric dipole or → magnetic dipole.

→ dipole; → radiation.

A localized source on the celestial sphere that can be observationally separated at radio wavelengths from its background emission.

→ discrete; → radio; → source.

In atomic physics, the broadening of an emission or absorption line due to the Doppler effect. Random motions of molecules or atoms of the gas that is emitting or absorbing the radiant energy shift the apparent wavelength of each emitter, and the cumulative effect of indivisual shifts is to broaden the line.

→ Doppler effect; → broadening.

The Swordfish. A constellation in the southern hemisphere near → Reticulum and → Pictor. It contains most of the → Large Magellanic Cloud which laps over to some extent into the neighboring constellation → Mensa. The south → ecliptic pole also lies within this constellation. Abbreviation: Dor, Genitive: Doradus.

Dorado, from Sp., from L.L. deaurutus, p.p. of deaurare "to gild," from → de- + aurium "gold." Dorado (Coryphaena hippurus) is a surface-dwelling fish found in off-shore tropical and subtropical waters worldwide. It is distinguished by dazzling golden colors on the sides.

Mâhi "fish," from Mid.Pers. mâhik, Av. masya-, cf. Skt. matsya-, Pali maccha-.
Zarrin "golden," from zarr "gold," Mid.Pers. zarr, Av. zaranya-, zarənu- "gold," O.Pers. daraniya- "gold," Skt. hiranya- "gold;" also Av. zaray-, zairi- "yellow, green," Mod.Pers. zard "yellow," Skt. hari- "yellow, green," Gk. Khloe lit. "young green shoot," L. helvus "yellowish, bay," Rus. zeltyj "yellow," P.Gmc. *gelwaz, Du. geel, Ger. gelb, E. yellow.

A → galaxy that emits radio energy from two regions located on opposite sides of the galaxy.

→ double; → lobe; → radio; → source.

1) A downward slope, especially of a road.
2) To assign to a lower status; to minimize the importance of (Dictionary.com).

→ down; → grade.

1) To transfer data from any other computer to one's computer.
2) The act of downloading.

→ down; → load.

Bârgereftan, literally "to take load," from bâr, → load, + gereftan "to take," → receiver; bârgiri, verbal noun of bârgereftan.

A → braneworld theory in which the → space-time is locally embedded in a five dimensional space, the → bulk, and has as a key aspect leakage of gravitational energy into the bulk. More specifically, the → graviton is pinned to a four-dimensional braneworld by intrinsic curvature terms induced by quantum matter fluctuations. But as it propagates over large distances, the graviton eventually evaporates off the brane into an infinite volume, five-dimensional Minkowski bulk. Therefore, the DGP braneworld theory is a model in a class of theories in which gravity deviates from conventional → General Relativity not at short distances, but rather at long distances. This means that at those distances General Relativity cannot correctly describe gravitational interactions. This model has various cosmologically interesting features. Particularly in the model with five dimensional bulk, the → accelerating expansion of the Universe at late epoch is realized without introducing the → cosmological constant (see, e.g., A. Lue, 2002, arxiv.0208169, T. Tanaka, 2003, arXiv.0305031).

G. Dvali, G. Gabadadze and M. Porrati, 2000, Phys. Lett. 485B, 208.

The distance from the Earth's center to its surface, about 6,371 km.

→ earth; → radius.

Of a galaxy, the distance from its center within which half of the total luminosity is included.

→ effective; → radius.

In gravitational lens phenomenon, the critical distance from the → lensing object for which the light ray from the source is deflected to the observer, provided that the source, the lens, and the observer are exactly aligned. Consider a massive object (the lens) situated exactly on the line of sight from Earth to a background source. The light rays from the source passing the lens at different distances are bent toward the lens. Since the bending angle for a light ray increases with decreasing distance from the lens, there is a critical distance such that the ray will be deflected just enough to hit the Earth. This distance is called the Einstein radius. By rotational symmetry about the Earth-source axis, an observer on Earth with perfect resolution would see the source lensed into an annulus, called Einstein ring, centered on its position. The size of an Einstein ring is given by the Einstein radius: θ_E = (4GM/c²)^0.5 (d_LS/(d_L.d_S)^0.5, where G is the → gravitational constant, M is the mass of the lens, c is the → speed of light, d_L is the angular diameter distance to the lens, d_S is the angular diameter distance to the source, and d_LS is the angular diameter distance between the lens and the source. The equation can be simplified to: θ_E = (0''.9) (M/10¹¹Msun)^0.5 (D/Gpc)^-0.5. Hence, for a dense cluster with mass M ~ 10 × 10¹⁵ Msun at a distance of 1 Gigaparsec (1 Gpc) this radius is about 100 arcsec. For a gravitational → microlensing event (with masses of order 1 Msun) at galactic distances (say D ~ 3 kpc), the typical Einstein radius would be of order milli-arcseconds.

→ Einstein; → radius.

→ EPR paradox.

A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Phys. Rev. 41, 777 (15 May 1935); → paradox.

Radiation propagating in the form of an advancing wave in electric and magnetic fields. It includes radio waves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

→ electromagnetic; → radiation.

The classical size of the electron given by r_e = e²/m_ec² = 2.81794 × 10^-13 cm, where e and m_e are the → electron charge and → electron mass, respectively, and c is the → speed of light.

→ electron; → radius.

The eighth of → Saturn's known → satellites, discovered by Herschel in 1789. It is about 500 km in diameter and orbits Saturn at a mean distance of 238,000 km with a period of 1.37 days. Enceladus has the highest → albedo (> 0.9) of any body in the → Solar System. Its surface is dominated by clean ice. Geophysical data from the → Cassini-Huygens spacecraft imply the presence of a global → ocean below an ice shell with an average thickness of 20-25 km, thinning to just 1-5 km over the south polar region. There, → jets of → water vapor and icy grains are launched through fissures in the → ice. The composition of the ejected material measured by Cassini includes salts and silica dust. In order to explain these observations, an abnormally high heat power is required, about 100 times more than is expected to be generated by the natural → decay of → radioactive elements in rocks in its core, as well as a means of focusing activity at the south pole. According to simulations, the core is made of unconsolidated, easily deformable, porous rock that water can easily permeate. The → tidal friction from Saturn is thought to be at the origin of the eruptions deforming the icy shell by push-pull motions as the moon follows an elliptical path around the giant planet. But the energy produced by tidal friction in the ice, by itself, would be too weak to counterbalance the heat loss seen from the ocean; the globe would freeze within 30 million years. More than 10 GW of heat can be generated by tidal friction inside the rocky core. Water transport in the tidally heated permeable core results in hot narrow upwellings with temperatures exceeding 90 °C, characterized by powerful (1-5 GW) hotspots at the seafloor, particularly at the south pole. The release of heat in narrow regions favors intense interaction between water and rock, and the transport of hydrothermal products from the core to the plume sources (Choblet et al., 2017, Nature Astronomy, doi:10.1038/s41550-017-0289-8)

In Gk. mythology Enceladus was a Titan who battled Athene in their war against the gods. When he fled the battlefield, Athene crushed him beneath the Sicilian Mount Etna.

Enkelâdos, from the original Gk. pronunciation of the name.