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

Of or relating to a → corona.

Adj., from → corona + → -al.

A part of the → solar corona where the gas density and the temperature are higher than in its vicinity. The coronal condensations are visible on the solar limb, above → sunspot groups. Images in X-rays and those supplied by → coronagraphs in white light reveal that such condensations consist of structures in the form of nodes, underlining the corona magnetic field (M.S.: SDE).

→ coronal; → condensation.

Several phenomena occurring in the Sun's corona, such as a → helmet streamer, → polar plume, → coronal loop, → coronal hole.

→ coronal; → feature.

A component of the → interstellar medium in the Galaxy which appears as pockets of gas at temperatures of over one million degrees, but extremely low densities of 10⁴ atoms per cubic centimeter. The hot coronal gas is believed to be material blown out of violent supernova explosions. It is called "coronal gas", after a similarity with the hot gas in → solar corona.

→ coronal; → gas.

An area in the → solar corona which appears dark in X-rays and ultraviolet light. The gas density in these areas are very low, about 100 times less than that of coronal → active regions. The magnetic field lines in a coronal hole extend out into → interplanetary space rather than returning to the Sun's surface, as they do in other parts of the Sun (→ open magnetic field line). Ionized hot gas can escape easily along such a path, and this brings about high speed → solar wind streams.

→ coronal; → hole.

An → emission line in the spectrum of the → solar corona caused by highly ionized metal ions; especially those of iron, such as the red and green lines at 6375 Å and 5303 Å [Fe X] (Fe⁹⁺ ion) and [Fe XIV] (Fe¹³⁺ ion), respectively. From their discovery in 1870 until 1939, it was believed that these → forbidden lines would be due to an unknown element, called → coronium. Ultraviolet and X-ray coronal lines are also detectable in stars.

→ coronal; → line.

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.

→ coronal; → loop.

A huge eruption of material from regions of the solar corona in which the magnetic field is closed, but which suffer an extremely energetic disruption. Over the course of several hours up to 10,000 billion kg of this material is ejected into → interplanetary space with a a speed of as high as 3000 km/s. CMEs are most spectacularly observed by a white light coronagraph located outside Earth's atmosphere. Such observations from Skylab in the early 1970's were the first to reveal this phenomenon. CME's disrupt the flow of the → solar wind and can produce intense electromagnetic disturbances that can severely damage satellites and disrupt power grids on Earth. When these ejections reach the Earth, they give rise to → geomagnetic storms. The frequency varies with the → solar cycle; during solar minimum they come at a rate of about one per week, and during maximum there is an average of about two or three per day. See also → interplanetary coronal mass ejections (ICME).

→ coronal; → mass; → ejection.

Material that condenses in the Sun's corona and appears to rain down into the chromosphere, as observed at the solar limb above strong sunspots.

→ coronal; → rain.

A bright, narrow stream of particles traveling through the Sun's corona, visible in images taken with a coronagraph or during a total solar eclipse. Coronal streamers represent the most outwardly extended structures in the solar corona and result from the interaction between the solar slow wind and the large-scale magnetic field. → helmet streamer.

→ coronal; → streamer.

An → interplanetary manifestation of a → coronal mass ejection.

→ interplanetary; → coronal; → mass; → ejection.