Fr.: Delta Cephée
The prototype of classical → Cepheid variables, which is a pulsating → yellow supergiant. John Goodricke was the first in 1784 to discover its variability. The star shows a quick and sharp rise from minimum to maximum, and slowly declines to its minimum again. The changes in brightness are accompanied by and principally caused by changes in stellar temperature and also by changes in radius. δ Cephei was actually the second Cepheid variable to be discovered. The first one, Eta Aquilae, had been discovered earlier the same year by Edward Pigott. δ Cephei varies with a period of 5.366341 days (or 5 days 8 hours 37.5 minutes) from magnitude 3.48, spectral type F5 Ib in its maximum to magnitude 4.37, spectral type G2 Ib in its minimum. It lies at a distance of 1,340 → light-years.
râne-ye deltâ , ~ vâkil
Fr.: entraînement en déclinaison
Fr.: fonction delta
Same as → Dirac function.
Fr.: offset en déclinaison
Fr.: delta Orionis
Same as → Mintaka.
Delta Scuti variable
Fr.: variable δ Scuti
A member of a class of → pulsating stars with periods less than 0.3 days, → spectral types A or F, and visual light amplitudes in the range from a few thousands of a magnitude to about 0.8 mag. On the → H-R diagram, δ Scuti stars form a group which lies in an → instability strip which includes the classical → Cepheids at its brightest end and the pulsating → white dwarfs at its faintest limit. These stars can show very complex light variations since, while some of them are pulsating in one radial mode only, others may be pulsating simultaneously in several radial and non-radial modes.
Deltâ T (ΔT)
Fr.: Delta T (ΔT)
A measure of the variation in → Earth's rotation, which is the difference between → Terrestrial Time (TT) and → Universal Time (UT). TT is uniform and related to the → International Atomic Time, whereas UT, which is directly tied to the Earth's rotation, is not strictly uniform and shows small erratic fluctuations. Between 1970 and 1990, ΔT changed from +40 to +57 seconds, and was +67 seconds for 2010.
Δ, Gk. letter of alphabet indicating a difference; T for → time.
In communications, the process of recovering the original information from a modulated signal wave. → modulation.
From L. dæmon "spirit," from Gk. daimon "deity, fate, fortune."
Pari "a good genius, a fairy," from Mid.Pers. parîk "sorceress, witch;" from Av. pairikā- "sorceress, witch."
1) To make evident or establish by arguments or reasoning; prove.
From L. demonstratus, p.p. of demonstrare "to show, point out," from → de- + monstrare "to show," from monstrum "sign, portent."
Padišidan, from Sogd. padēš "to show," ultimately from Proto-Ir. *apa-dais-, from *dais- "to show," cf. Av. daēs- "to show," related to andiš, → think.
1) The → act or → circumstance
of proving or being → proved conclusively, as
by → reasoning or a show of → evidence.
Verbal noun of → demonstrate.
A person or thing that demonstrates (Dictionary.com).
The removal of mystery or confusion surrounding a topic or idea.
To rid of mystery or obscurity; clarify. The removal of mystery or confusion surrounding a topic or idea.
1) A branching treelike figure produced on or in a mineral by a foreign
From Gk. dendrites "of or pertaining to a tree," from dendron "tree," cognate with Pers. deraxt, variant dâr, → tree.
Šâxzâré, from šâxzâr, from šâxsâr "full of branches," from šâx, šâxé, → branch, + suffix -zâr denoting profusion, and abundance, as in kârzâr "a field of battle; combat" šurezâr "unfertile, salty ground; nitrous earth," xoškzâr "arid land," and so forth.
The branch of → botany dealing with trees and shrubs. Dendrology studies the distinguishing characteristics of tree species for the purpose of identification and classification into orders and other natural groups.
Deneb (α Cygni)
Deneb "tail," from Ar. dhanab ad-dajajah (
Zanab, from Ar., as above.
Denebola (β Leonis)
Širdom, Zanab-ol-asad (#)
Denebola, from Ar. dhanab al-asad (
Fr.: dénégation, démenti
1) An assertion that something said, believed, alleged, etc., is false.
1) To give a specific name to.