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The strength of seeing is often characterized by the angular diameter of the long-exposure image of a star (seeing disk) or by the Fried parameter r 0. The diameter of the seeing disk is the full width at half maximum of its optical intensity. An exposure time of several tens of milliseconds can be considered long in this context. The Fried ...
Turbulent flow is defined as the flow in which the system's inertial forces are dominant over the viscous forces. This phenomenon is described by Reynolds number, a unit-less number used to determine when turbulent flow will occur. Conceptually, the Reynolds number is the ratio between inertial forces and viscous forces. [6]
Astrophysical fluid dynamics is a branch of modern astronomy which deals with the motion of fluids in outer space using fluid mechanics, such as those that make up the Sun and other stars. [1] The subject covers the fundamentals of fluid mechanics using various equations , such as continuity equations , the Navier–Stokes equations , and Euler ...
This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a ...
The first Friedmann equation contains a discrete parameter k = +1, 0 or −1 depending on whether the shape of the universe is a closed 3-sphere, flat (Euclidean space) or an open 3-hyperboloid, respectively. [5] If k is positive, then the universe is "closed": starting off on some paths through the universe return to the starting point. Such a ...
The scale is a five-point system, with 1 being the best seeing conditions and 5 being the worst. The actual definitions are as follows: (I.) Perfect seeing, without a quiver. (II.) Slight quivering of the image with moments of calm lasting several seconds. (III.) Moderate seeing with larger air tremors that blur the image. (IV.)
[65] [66] The average surface pressure on Mars today is close to that of the triple point of water; thus, liquid water cannot exist there. [ 67 ] [ 68 ] Planets with high-pressure atmospheres may have liquid surface water, but life forms would have difficulty with respiratory systems at high-pressure [ quantify ] atmospheres.
Open Astronomy (formerly Baltic Astronomy) is a peer-reviewed fully open access scientific journal, and currently published by De Gruyter Open.The journal was established in 1992 by the Institute of Theoretical Physics and Astronomy (Vilnius University, Lithuania) as Baltic Astronomy, obtaining its current title in 2017 when it converted to open access.