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Tidal-current and tidal-range power
Published in John Twidell, Renewable Energy Resources, 2021
To calculate tidal periods, we must carefully define a ‘day’ (see Fig. 12.4). At a point A on the Earth, a solar day is the interval between when the Sun crosses the meridional plane at A on a specified day and when it does so on the subsequent day. This period actually varies through the year owing to the irregularities of the Earth's orbit, and so the common unit of time, the mean solar day tS, is defined to be the interval averaged over a whole year. Its value is defined as exactly 24 hours, i.e. tS=24.0000h×60minh×60smin=86400s
Definitions and Terminology
Published in Frank Vignola, Joseph Michalsky, Thomas Stoffel, Solar and Infrared Radiation Measurements, 2019
Frank Vignola, Joseph Michalsky, Thomas Stoffel
Before these celestial coordinates can be related to a more convenient local coordinate system, a time adjustment factor known as the equation of time (EoT) needs to be discussed. Refer again to Figure 2.2. Let’s assume that the Earth orbits the Sun in a perfect circle. The Earth rotates counterclockwise on its axis at a virtually constant rate because of the conservation of angular momentum. A solar day is defined by the time it takes for the Sun to appear at the same point in the sky. This is the time to complete one rotation plus a little more; this extra rotation is because the Earth rotates counterclockwise with respect to the North Pole and also moves counterclockwise 1/365.25th of the way around its orbit meaning that the Sun appears to have moved in the heavens from the previous day by this much. One day equals 24 hours or 1,440 minutes, and 1/365.25th of 1,440 minutes is just under 4 minutes. Note that a sidereal day is defined by the time it takes the Earth to complete one rotation, and it is about 4 minutes shorter than a solar day of 1,440 minutes.
Analysis of building structures and valorization of cultural heritage in Jeddah (KSA)
Published in Koen Van Balen, Els Verstrynge, Structural Analysis of Historical Constructions: Anamnesis, Diagnosis, Therapy, Controls, 2016
C. Jäger-Klein, W. Stumpf, G. Styhler-Aydin, G. Radinger
The city of Jeddah is located just south of the Tropic of Cancer at latitude 21 32 North, 39 10 East on the Red Sea coast of Saudi-Arabia. The length of the solar day varies between 13h 25min in summer (June 21st) and 10h 51min in winter (December 21st). Midday solar irradiation angles attain 90 in July and 45 in December. The local climate is characterized by an annual global irradiation value of 2168 kWh/m2 with highest levels reached in May (227 W/m2 month) and lowest
Rotational modes of Poincaré Earth models
Published in Geophysical & Astrophysical Fluid Dynamics, 2021
With research in Earth Rotation, (ii) above, we refer to the line of research primarily concerned with the Earth's wobble and nutation (e.g. Hough 1895, Poincaré 1910, Jeffreys and Vicente 1957, Molodensky 1961, Smith 1974, 1977, Sasao et al.1980, Wahr 1981, Mathews et al.1991, Rogister 2001, Mathews et al.2002, Rochester and Crossley 2009, Rochester et al.2014, Dehant and Mathews 2015, Seyed-Mahmoud et al.2017). Wobble and nutation refer to the same phenomenon according as whether it is observed (computed) in a terrestrial (rotating) frame or a celestial (fixed) frame. Accordingly, the frequency, , of a wobble mode is related to that of the associated nutation mode, , as where Ω is the Earth's rotation rate and m is the azimuthal wavenumber. Here we would also like to clarify a point about a solar day and a sidereal day (sd). In Earth rotation, the length of day is usually measured as sd rather than a solar day. A solar day is, of course, the time that takes the Earth to make a full revolution with respect to the sun. A sidereal day, on the other hand, is the time that takes the Earth to make a full rotation with respect to another fixed star. Since the Earth orbits the sun in a prograde (same direction as the Earth's spin) sense, a sd, approximately 23 hours 56 minutes and 4 seconds, is slightly shorter than a solar day.