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

The instant of time when the object is in the West and the geometric → zenith distance is equal to 90° plus the → horizontal refraction plus the semidiameter minus the → parallax.

→ apparent; → setting.

The decrease in the intensity of light from a celestial body due to absorption and scattering by Earth's atmosphere. It increases from the zenith to the horizon and affects short wavelengths more than long wavelengths, so that objects near the horizon appear redder than they do at the zenith.

→ atmospheric; → extinction.

A continuous range of wavelengths in the Balmer spectrum of hydrogen corresponding to transitions between the energy levels n = 2 and n = ∞.

→ Balmer; → continuum.

An abrupt decrease in the intensity of the continuum at the limit of the → Balmer series of hydrogen (at about 3650 Å), caused by the energy absorbed when electrons originally in the second → energy level are ionized. Same as → Balmer jump.

→ Balmer; → discontinuity.

→ line blanketing.

→ line blanketing.

A → diffraction grating ruled appropriately so that a large proportion of the diffracted light is concentrated into a few, or even a single → order of interference.

Blazed, adj. of → blaze; → grating.

Turi, noun from tur "a net, a fishing net;" belizi adj. from beliz, → blaze.

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

→ blue; → continuum.

The action or quality of a → co-orbiting asteroid.

From co- "together," → com- + → orbit + → -ing.

From ham- "together," → com- + madâr→ orbit + -i noun suffix.

An asteroid having a → co-orbital motion.

→ co-orbiting; → asteroid.

The unpowered flight of a spacecraft or missile after propulsion cutoff or between the burnout of one stage and the ignition of the next.

Coasting, verbal adjective from → coast; → flight.

A Universe whose density is just less than or equal to the critical value and expands forever with no change in the expansion rate.

Coasting, verbal adjective from → coast; → Universe.

A → thin → layer of a → substance spread over a → surface.

Noun from → coat; → -ing.

Of an interferometric telescope made up of several mirrors, the hypothetical mirror created by the combination of the individual mirrors.

→ collect; → area.

A physical process whereby heat is imparted to (e.g. → interstellar dust grains or → molecular hydrogen) through collisions (with hot electrons, ions, etc.).

→ collisional; → heating.

A → diffraction grating ruled on a concave spherical mirror that eliminates chromatic aberration and transmits regions of the spectrum, such as the ultraviolet, which is not transmitted by glass lenses.

→ concave; → grating.

Any of the large, continuous land areas of the Earth. They are usually considered to be seven: Europe, Asia, Africa, North America, South America, Australia, and Antarctica.

Contraction of L. terra continens "continuous land," from continens, pr.p. of continere "to hold together," from → com- "together" + tenere "to hold, to keep, to maintain" from PIE root *ten- "to stretch;" → tension.

Qâré, from Ar. qârrat.

Of or of the nature of a continent.

→ continent; → -al.

The part of the → Earth's crust which underlies the → continents. Continental crust is more silica-rich and thicker than → oceanic crust, and is on average older. However, it is highly variable in all of these respects. The average thickness of the continental crust is about 40km, but beneath parts of the Andes and the Himalaya mountain ranges the crust is more than 70 km thick. Continental crust is continuously being eroded and turned into sediment. Some of this sediment ends up on the ocean floor where it can be returned to the → Earth's mantle at → subduction zones. The oldest parts of the continental crust include some rocks that are nearly 4 billion years old. New continental crust is produced by the destruction of oceanic crust at subduction zones, a process that continues today.

→ continental; → crust.

A hypothesis proposed by Alfred Wegener (1912) suggesting that the → continents are not stationary, but drift through time. Wegener's hypothesis has since been developed and included in a new theory called → plate tectonics.

→ continental; → drift.