Ut Universal Time

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Universal Time ( UTC ) to Your Local Time and Worldwide Time Conversions, Conversion Time Chart between Universal Time and Local Time.

  • Time difference between your local time and UTC is: -7 hour (s) (-420 minutes). latin ante meridiem, meaning before midday, PM or P.M. latin post meridiem, meaning after midday. Letter 'Z' in military time indicates ZULU Time Zone which is equivalent to UTC.
  • Universal Time Coordinated / Universal Coordinated Time: Successor to: Greenwich Mean Time (GMT) Military name: “Zulu” Military Time: Longitude: 0° (Prime Meridian) At sea: Longitudes between 7.5° West and 7.5° East: Note: United Kingdom is one hour ahead of UTC / GMT during summer.

Universal time (UT) is simply the number of hours, minutes, and seconds which have elapsed since midnight (when theSun is at a longitude of 180°) in the Greenwich time zone.

Since the Earth's rotation is irregular at the 0.1 second level, a local approximation to universal time not correctedfor polar motion is often used. This is called UT0, and also referred to as Greenwich mean time, abbreviated GMT. InUT0, 24 universal hours are defined to be a mean solar day.

Ut Universal Time

The following table gives the conversions between universal time (UT) and standard anddaylight saving time in the United States.

standard time zonehours to add to UTdaylight saving time zonehours to add to UT
Eastern standard time (EST)-5Eastern daylight time (EDT)-4
Central standard time (CST)-6Central daylight time (CDT)-5
Mountain standard time (MST)-7Mountain daylight time (MDT)-6
Pacific standard time (PST)-8Pacific daylight time (PDT)-7

The actual universal time (denoted UT or UT1) is tied to the rotation of the Earth. Because the Earth'srotation rate is rather irregular and unpredictable at the 0.1 s level, Universal Time can only be deduced fromobservations of star transits. Once known, UT can be compared with known ephemeris time, and the difference can be derived. UT is always kept within 0.9 seconds of coordinated universal time (what WWV andother time broadcast services provide) by the insertion or deletion of leap seconds, usually at23:59:59 UTC on either June 30 or December 31. The following table gives for 1990-2000 (AstronomicalAlmanac, p. K9), where indicates an extrapolated value.

YearYear
1990.056.862000.0
1991.057.572001.0
1992.058.312002.0
1993.059.122003.0
1994.059.982004.0
1995.060.78
1996.061.63
1997.062.29
1998.062.97
1999.0

Barycentric Dynamical Time, Coordinated Universal Time, Daylight Saving Time, Ephemeris Time, Greenwich Mean Time, International Atomic Time, Standard Time, Time



Duffett-Smith, P. 'Converting the Local Time to UT,' 'Converting UT to Local Civil Time,' '`Sidereal Time,' 'Conversion of UT to GST,' and 'Conversion of GST to UT.' §9-13 in Practical Astronomy with Your Calculator, 3rd ed. Cambridge, England: Cambridge University Press, pp. 12-19, 1992.

Jones, T. Splitting the Second: The Story of Atomic Time. Bristol, England: Institute of Physics Publishing, 2000.

Montenbruck, O. and Pfleger, T. 'Universal Time and Ephemeris Time.' §3.4 in Astronomy on the Personal Computer, 4th ed. Berlin: Springer-Verlag, pp. 41-44, 2000.

United States Government Printing Office. The Astronomical Almanac for the Year 2000. Washington, DC: Navy Dept., Naval Observatory, Nautical Almanac Office, p. K9, 2000.



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Universal Time: UTC, UT1

Coordinated Universal Time UTC is the basis of civil timekeeping.Most time zones differ from UTC by an integer numberof hours, though a few (e.g. parts of Canada and Australia) differby n+0.5 hours. The UTC second is the same as the SI second,as for TAI. In the long term, UTC keeps in step with theSun. It does so even though the Earth's rotation is slightlyvariable (due to large scale movements of water and atmosphereamong other things) by occasionally introducing a See full list on utctime.netleapsecond.

Universal Time UT, or more specifically UT1,is in effect the mean solar time. It is continuous(i.e. there are no leap seconds) but has a variablerate because of the Earth's non-uniform rotation period. It isneeded for computing the sidereal time, an essential part ofpointing a telescope at a celestial source. To obtain UT1, youhave to look up the value of UT1-UTC for the date concernedin tables published by the International Earth RotationService; this quantity, kept in the range by means of UTC leapseconds, is then added to the UTC. The quantity UT1-UTC,which typically changes by 1 or 2 ms per day,can only be obtained by observation, though seasonal trendsare known and the IERS listings are able to predict some way intothe future with adequate accuracy for pointing telescopes.

UTC leap seconds are introduced as necessary,usually at the end of December or June.On the average the solar day is slightly longerthan the nominal 86,400 SI seconds and so leap seconds are always positive;however, provision exists for negative leap seconds if needed.The form of a leap second can be seen from thefollowing description of the end of June 1994:

Figure 1:Relationship Between Celestial Coordinates
date rather than a time. Though the routines will accepta fractional part and will almost always function correctly, on a daywhich ends with a leapsecond incorrect results would be obtained during the leap seconditself because by then the MJD would have moved into the next day.



Universal Time Utc Now

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Ut Universal Time


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TimeSLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
25 January 2000
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