I want to convert the Julian date 273.791667 to calendar day and time

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Thishan Dharshana Karandana Gamalathge 2017-7-20

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评论： James Tursa 2017-7-20

采纳的回答： Chad Greene

I want to convert the Julian date 273.791667 to calandar day and time

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James Tursa 2017-7-20

编辑：James Tursa 2017-7-20

As a nit, that number should be referred to as "day of year" and not "Julian date". I know there are segments of the scientific community that call it a "Julian date", but that usage is confusing at best. E.g., the definition of the term from the USNO:

http://aa.usno.navy.mil/data/docs/JulianDate.php

You will find variations of this term in the literature depending on the underlying time scale (e.g., UT or TT) and 0 point, but even these are not "day of the year" types of measures.

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Chad Greene 2017-7-20

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You'll have to specify a year, but for 2017 you can get a date vector like this:

datevec(datenum(2017,0, 273.791667))

or a date string like this:

datestr(datenum(2017,0, 273.791667))

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Thishan Dharshana Karandana Gamalathge 2017-7-20

编辑：James Tursa 2017-7-20

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From a .mat file "X" with size(10x8), I am trying to calculate Z. But the following code gives an error. i cannot figure out the reason. Please help me with that. Thanks.

load X
for i=1:10
        Y(i)=X(i,1);
    UTC_start_time(i)=datevec(datenum(2010,0,Y(i,1)));
end

James Tursa 2017-7-20

datevec returns a vector. You cannot stuff a vector into a single element.

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Steven Lord 2017-7-20

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Use datetime. You can 'ConvertFrom' 'juliandate' (Number of days since noon UTC 24-Nov-4714 BCE (proleptic Gregorian calendar)) or 'modifiedjuliandate' (Number of days since midnight UTC 17-Nov-1858).

If you want to determine what the 273.791667th day of the year is, try something like this. Check the day of the year using the day function with the 'dayofyear' option:

x = datetime(2017, 1, 0) + days(273.791667)
day(x, 'dayofyear')

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Walter Roberson 2017-7-20

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If you want to specify that this was UTC, you can use

x = datetime(2017, 1, 0, 'TimeZone', 'UTC') + days(273.791667)

and if you then want to see it in local time,

x.TimeZone = 'local'

Note that this is not the same as

x = datetime(2017, 1, 0, 'TimeZone', 'local') + days(273.791667)

In order for the timezone conversion to be done properly, you need to set to UTC first and then change the timezone; if you just set the timezone directly like in this second example then MATLAB will assume that you mean that the given date/time information is being stated relative to your timezone.

Thishan Dharshana Karandana Gamalathge 2017-7-20