DeltaT
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Contents: Description, Arguments, Usage, Examples, Sub-Functions, Related Functions, Source Supported Under Version: > 1.15
Description Find TT-UTC offset (Delta-T), given UTC Julian Date
Arguments and Return Values Parameters: Numeric array specifying the Julian Dates for which to find Delta-T. If also given a nonzero second input (and the first input has a z-dimension of 1), the function will also return the estimated uncertainty in Delta-T. Return Value: Double-precision TT-UTC offsets, in seconds
Usage Syntax: DeltaT(JD, mode) The Julian Date (JD) is a continuous count of days since noon UTC on January 1, 4713 BCE in the proleptic Julian calendar. Coordinated Universal Time (UTC) is the basis for the time system used in everyday life. In order to keep UTC consistent with the Earth's slightly variable rate of rotation, leap seconds are occasionally inserted into UTC. Terrestrial Time (TT) is a time system with no leap seconds. This function finds the difference between the two for the user-specified dates/times. For 1961 and after, this function uses a table to account for leap seconds and other adjustments. Before 1961, it estimates the correction based on historical eclipse records (from Morrison and Stephenson 2004). Therefore the returned values are perfectly accurate for 1961 to the near future, but there is some uncertainty in Delta-T before 1961 and more than a few months in the future (since leap seconds cannot be predicted very far in advance). For more information, see
When DeltaT() is entered without any arguments, it prints its description, as shown below.
Examples dv> DeltaT() Find TT-UTC offset (Delta-T), given UTC Julian Date Works for array inputs DeltaT(JD) returns double-precision TT-UTC offset, in seconds If also given a nonzero second input (and the first input has a z-dimension of 1), e.g. DeltaT(2086308,1), the function will also return the estimated uncertainty in Delta-T. For 1961 and after, uses table to account for leap seconds and other adjustments. Before 1961, estimates correction based on historical eclipse records (from Morrison and Stephenson 2004). Therefore the returned values are perfectly accurate for 1961 to the near future, but there is some uncertainty in Delta-T before 1961 and more than a few months in the future (since leap seconds cannot be predicted very far in advance). See http://www.giss.nasa.gov/tools/mars24/help/algorithm.html, http://tycho.usno.navy.mil/leapsec.html, ftp://maia.usno.navy.mil/ser7/tai-utc.dat, http://heasarc.gsfc.nasa.gov/docs/xte/abc/time_tutorial.html, http://adsabs.harvard.edu/abs/2004JHA....35..327M (M&S 2004), and http://adsabs.harvard.edu/abs/2005JHA....36..339M (addendum). S.Marshall 01-23-2010 0 dv> DeltaT(JD(2010, 1, 1)) 66.1840000000000 dv> DeltaT(JD(2000, 1, 1)) 64.1840000000000 dv> a = create(1, 17, start=1800, step=10) 1x17x1 array of int, bsq format [68 bytes] dv> double(a)//DeltaT(JD(a, 1, 1), 1) 3x17x1 array of double, bsq format [408 bytes] 1800.00000000000 14.0000000000000 1.00000000000000 1810.00000000000 13.0000000000000 1.00000000000000 1820.00000000000 12.0000000000000 1.00000000000000 1830.00000000000 8.00000000000000 0.930000007152557 1840.00000000000 6.00000000000000 0.860000014305115 1850.00000000000 7.00000000000000 0.790000021457672 1860.00000000000 8.00000000000000 0.720000028610229 1870.00000000000 2.00000000000000 0.649999976158142 1880.00000000000 -5.00000000000000 0.579999983310699 1890.00000000000 -6.00000000000000 0.509999990463257 1900.00000000000 -3.00000000000000 0.439999997615814 1910.00000000000 10.0000000000000 0.370000004768372 1920.00000000000 21.0000000000000 0.300000011920929 1930.00000000000 24.0000000000000 0.230000004172325 1940.00000000000 24.0000000000000 0.159999996423721 1950.00000000000 29.0000000000000 0.100000001490116 1960.00000000000 33.0000000000000 0.100000001490116 dv> a = create(1, 11, start=1960, step=5) 1x11x1 array of int, bsq format [44 bytes] dv> double(a)//DeltaT(JD(a, 1, 1), 1) 3x11x1 array of double, bsq format [264 bytes] 1960.00000000000 33.0000000000000 0.100000001490116 1965.00000000000 35.7247780000000 0.00000000000000 1970.00000000000 40.1853780000000 0.00000000000000 1975.00000000000 46.1840000000000 0.00000000000000 1980.00000000000 51.1840000000000 0.00000000000000 1985.00000000000 54.1840000000000 0.00000000000000 1990.00000000000 57.1840000000000 0.00000000000000 1995.00000000000 61.1840000000000 0.00000000000000 2000.00000000000 64.1840000000000 0.00000000000000 2005.00000000000 64.1840000000000 0.00000000000000 2010.00000000000 66.1840000000000 0.00000000000000 |
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Recent Library Changes Created On: 11-18-2009 |
