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Julian Date conversions
- Thread starter goldnhwk
- Start date
well... it's been so long since I've actually worked in QBASIC 
) so I can't remember how to do dates at all... what are you working with so far? What do you have already? There's probably a way to do it that isn't language-specific, I can probably help you if I know where you're at at the moment. <p>Liam Morley<br><a href=mailto:lmorley@wpi.edu>lmorley@wpi.edu</a><br><a href= imotic ::</a><br>
) so I can't remember how to do dates at all... what are you working with so far? What do you have already? There's probably a way to do it that isn't language-specific, I can probably help you if I know where you're at at the moment. <p>Liam Morley<br><a href=mailto:lmorley@wpi.edu>lmorley@wpi.edu</a><br><a href= imotic ::</a><br>Hmmm....I'm not sure on the Julian dates part....not remembering that calendar very well; but if you give me a description of the diff. between Julian & real-world I'm sure I could come up with a little more help for you 
<p>-Robherc<br><a href=mailto:robherc@netzero.net>robherc@netzero.net</a><br><a href= shared.freeservers.com/searchmaster.html>SearchMaster Interface...11-in-1</a><br>Wanting to learn Assembler; please e-mail me any tutorials or links for it that are useful to you 
<p>-Robherc<br><a href=mailto:robherc@netzero.net>robherc@netzero.net</a><br><a href= shared.freeservers.com/searchmaster.html>SearchMaster Interface...11-in-1</a><br>Wanting to learn Assembler; please e-mail me any tutorials or links for it that are useful to you 
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2.12. What is the Julian Period?<br>--------------------------------<br><br>The Julian period (and the Julian day number) must not be confused<br>with the Julian calendar. <br><br>The French scholar Joseph Justus Scaliger (1540-1609) was interested<br>in assigning a positive number to every year without having to worry<br>about BC/AD. He invented what is today known as the "Julian Period".<br><br>The Julian Period probably takes its name from the Julian calendar,<br>although it has been claimed that it is named after Scaliger's father,<br>the Italian scholar Julius Caesar Scaliger (1484-1558).<br><br>Scaliger's Julian period starts on 1 January 4713 BC (Julian calendar)<br>and lasts for 7980 years. AD 1998 is thus year 6711 in the Julian<br>period. After 7980 years the number starts from 1 again.<br><br>Why 4713 BC and why 7980 years? Well, in 4713 BC the Indiction, the Golden Number and the Solar<br>Number were all 1. The next times this happens is<br>15*19*28=7980 years later, in AD 3268.<br><br>Astronomers have used the Julian period to assign a unique number to<br>every day since 1 January 4713 BC. This is the so-called Julian Day<br>(JD). JD 0 designates the 24 hours from noon UTC on 1 January 4713 BC<br>to noon UTC on 2 January 4713 BC.<br><br>This means that at noon UTC on 1 January AD 2000, JD 2,451,545 will<br>start.<br><br>This can be calculated thus:<br> From 4713 BC to AD 2000 there are 6712 years.<br> In the Julian calendar, years have 365.25 days, so 6712 years<br> correspond to 6712*365.25=2,451,558 days. Subtract from this<br> the 13 days that the Gregorian calendar is ahead of the Julian<br> calendar, and you get 2,451,545.<br><br>Often fractions of Julian day numbers are used, so that 1 January AD<br>2000 at 15:00 UTC is referred to as JD 2,451,545.125.<br><br>Note that some people use the term "Julian day number" to refer to any<br>numbering of days. NASA, for example, use the term to denote the<br>number of days since 1 January of the current year.<br><br><br>2.12.1. Is there a formula for calculating the Julian day number?<br>-----------------------------------------------------------------<br><br>Try this one (the divisions are integer divisions, in which remainders<br>are discarded):<br><br> a = (14-month)/12<br> y = year+4800-a<br> m = month + 12*a - 3<br><br> For a date in the Gregorian calendar:<br> JDN = day + (153*m+2)/5 + y*365 + y/4 - y/100 + y/400 - 32045<br><br> For a date in the Julian calendar:<br> JDN = day + (153*m+2)/5 + y*365 + y/4 - 32083<br><br><br>JDN is the Julian day number that starts at noon UTC on the specified<br>date.<br><br>The algorithm works fine for AD dates. If you want to use it for BC<br>dates, you must first convert the BC year to a negative year (e.g.,<br>10 BC = -9). The algorith works correctly for all dates after 4800 BC,<br>i.e. at least for all positive Julian day numbers.<br><br><br>To convert the other way (i.e., to convert a Julian day number, JDN,<br>to a day, month, and year) these formulas can be used (again, the<br>divisions are integer divisions):<br><br> For the Gregorian calendar:<br> a = JDN + 32045<br> b = (4*(a+36524))/146097 - 1<br> c = a - (b*146097)/4<br><br> For the Julian calendar:<br> b = 0<br> c = JDN + 32083<br><br> Then, for both calendars:<br> d = (4*(c+365))/1461 - 1<br> e = c - (1461*d)/4<br> m = (5*(e-1)+2)/153<br><br> day = e - (153*m+2)/5<br> month = m + 3 - 12*(m/10)<br> year = b*100 + d - 4800 + m/10<br><br><br>2.12.2. What is the modified Julian day number?<br>-----------------------------------------------<br><br>Sometimes a modified Julian day number (MJD) is used which is<br>2,400,000.5 less than the Julian day number. This brings the numbers<br>into a more manageable numeric range and makes the day numbers change<br>at midnight UTC rather than noon.<br><br>MJD 0 thus started on 17 Nov 1858 (Gregorian) at 00:00:00 UTC.<br>
Hey <b>goldnhwk</b>, I've just happened to have gone through my old BASes and came across a few I got off the web.<br><br>And in one of them, I came across the following code (which you should be able to modify to your lit'l heart's content.)<br><br><br><FONT FACE=monospace><b>DECLARE FUNCTION DateToJulian! (Dat$)<br><br><br>FUNCTION DateToJulian! (Dat$)<br>'*******************************************************************************<br>'* converts gregorian-style mm/dd/yyyy date to julian date *<br>'*******************************************************************************<br> Month% = VAL(MID$(Dat$, 1, 2))<br> Day% = VAL(MID$(Dat$, 4, 2))<br> Year% = VAL(MID$(Dat$, 7, 4))<br><br> SELECT CASE Month%<br> CASE IS > 2<br> Month% = Month% - 3<br> CASE IS <= 2<br> Month% = Month% + 9<br> Year% = Year% - 1<br> END SELECT<br><br> A = 146097# * FIX(FIX(Year% / 100) / 4)<br> B = FIX(1461# * (Year% MOD 100) / 4)<br> C = FIX((153# * Month% + 2) / 5) + Day% + 1721119<br><br> DateToJulian = A + B + C<br><br>END FUNCTION</b></font><br><br>This may help I'm sure. Especially since you don't have to type it all in.<br><br>Just cut and paste away like me.<br>I'm MiggyD (HEY THAT RHYMES, WHAT DO YA KNOW!?!?)<br><br><i>[Note--couldn't resist the rhyming thing there.]</i> <p> <br><a href=mailto: > </a><br><a href= > </a><br>If a tree falls in the forest and there's no one around, does it make sound? Its not the sound that matters, but the silence it leaves behind.
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