Astronomical time

The United States Congress passed the Standard Time Act of 1918 to establish standard time and preserve and set Daylight Saving Time across the continent. This act also devised five time zones throughout the United States Eastern, Central, Mountain, Pacific, and Alaska. The (30) first time zone was set on the mean astronomical time of the seventy-... 

Scargle, J. D. (1982). Studies in astronomical time series analysis. II. Statistical aspects of spectral analysis of unevenly spaced data. Astroph. J., 263, 835-53. 

In contrast to the search for exotic events with a low probability, one can try to learn new physics with the help of high accuracy. The most promising way now is likely to look for a variation of results due to different circumstances. One possibility is a variation of fundamental constants with time. Some of these comparisons can be done over an astronomical time [37]. 

The universe is an excellent paradigm of an isolated and closed system. Ordinarily, events occurring at astronomical time scales may be ignored in the consideration of physical and chemical processes occurring in the laboratory. 

Tiedemann R., Sarnthein M., Shackleton N.J. (1994) Astronomic time scale for the Pliocene Atlantic 8lsO and dust flux records of Ocean Drilling Program Site 659. Paleoceanogr. 9, 619—38. 

The ultimate accuracy of such a clock depends upon a variety of factors. Theoretically it should be possible to obtain a permanent accuracy of 1 part in 10 billion (io1 ). At present I part in 10 million has been achieved. Such a clock can be used to improve our astronomical time standards being entirely constant and independent of the earth s movement it could be used, for example, to determine if the sidereal day is more constant than the mean solar day, as some authorities believe may be the case. Conversely it may be of great use to the radio-engineer as it could be used to control more rigidly the frequency of the waves emitted from various stations and thus make more efficient use of the available radio spectrum. This is very necessary if overlapping is to be avoided, because the present crowding has imposed severe limitations both nationally and internationally on the expanding use of radio for industry and communications. 

Local Solar Time - A system of astronomical time in which the sun crosses the true north-south meridian at 12 noon, and which differs from local time according to longitude, time zone, and equation of time. 

A similar analysis ean be applied to other reaction mechanism, such as parallel irreversible first-order reaetions A B and A—>C, a triangle of reversible first-order reactions and simple models with nonlinear dependencies. The results obtained for the temporal changes of concentrations can be direetly applied to steady-state PHI models, with the astronomic time replaced by the space time or residence time r. Similar analyses can also be done for CSTRs. 

A leap second is added to UTC every so often (usually less than once per year) to bring it into sync with the more stable astronomical time, which is based not on atomic clocks but on the rate at which the Earth rotates. 

The unit of time, the second, is abbreviated by small s (and not sec). For all measurement purposes it is the ephemeris second, the properly fked fraction of the mean solar year 1900. The SI unit is chosen to match this time-interval closely using a cesium 133 clock. This definition makes the SI time independent of the astronomical time. The cesium 133 clock is capable of an accuracy of one part in 10. An ordinary stopwatch, not even a quartz watch, is usually sufficient for thermal analysis experiments. 

There have been several definitions of the SI second. Until 1956, the definition was based on the mean solar day, or one revolution of the earth on its axis. The mean solar second was defined as 1/86,400 of the mean solar day and provided the basis for several astronomical time scales known as Urriversal Time (UT). 

UTl The most widely used astronomical time scale, UTl improves upon UTO by correcting for longitudirral shifts of the observing station due to polar motion. Since the earth s rotatiorral rate is not uniform the uncertainty of UTl is about 2 to 3 msec per day. 

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