Fr.: boucle de Barnard
A very faint nebular shell of huge size enveloping the central portion of Orion.
Fr.: boucle bleue
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.
Fr.: boucle coronale
An arc-like structure in the Sun's → corona that is found around → sunspots and in → active regions. These structures are associated with the closed magnetic field lines that connect magnetic regions on the solar surface. The loops are sometimes as high as 10,000 km with their two ends situated in photosphere regions of opposite magnetic polarity. This implies that the coronal loops are tubes of magnetic flux filled with hot plasma. They last for days or weeks but most change quite rapidly.
Fr.: boucle du Cygne
A large supernova remnant in the → constellation → Cygnus, some 80 light-years across, lying about 2,500 light-years away. The loop is expanding at over 100 km/s and is thought to be about 30 000 years old.
Fr.: boucle de rétroaction
Fr.: cycle d'hystérésis
A closed curve showing the change in magnetic induction of a ferromagnetic body to which an external field is applied as the intensity of this field is varied from +Hs to -Hs and back again, where Hs is the magnetic field intensity corresponding to saturation.
Anything shaped more or less like a loop, i.e. portion of a cord, ribbon, etc.,
folded or doubled upon itself.
Probably of Celtic origin (cf. Gael. lub "bend," Ir. lubiam), influenced by O.N. hlaup "a leap, run."
Gerdâl, from gerd "round, a circle" (Mid.Pers. girdag "disk, round," from gird/girt "round, all around," Proto-Iranian *gart- "to twist, to wreathe," cf. Skt krt "to twist threads, spin; to wind; to surround;" kata- "a twist of straw," Pali kata- "ring, bracelet," Gk. kartalos "a kind of basket," kyrtos "curved") + → -al.
Fr.: protubérance en boucle
A very bright active prominence in the form of a loop seen in Hα after a rather big flare. Also called "post-flare loops," they connect the feet where the two-ribbon flares were seen. The lifetime of loop prominences is several hours.
Fr.: Boucle du Loup
An large nonthermal radio source in the constellation → Lupus, identified as a very old supernova remnant. It is also an extended source of soft X-rays.
Fr.: Boucle de la Licorne
A faint filamentary loop of nebulosity about 1 kpc distant, the remnant of a supernova that occurred about 300,000 years ago. It contains the Rosette Nebula as well as the Cone Nebula.