1. Jun 15, 2007

lewis198

the julian day formula goes like this:

$$\begin{matrix}a & = & \left\lfloor\frac{14 - month}{12}\right\rfloor \\ \\y & = & year + 4800 - a \\ \\m & = & month + 12a - 3 \\\end{matrix}$$

For a date in the Gregorian calendar (at noon):

$$\begin{matrix}JDN & = & day + \left\lfloor\frac{153m + 2}{5}\right\rfloor + 365y + \left\lfloor\frac{y}{4}\right\rfloor - \left\lfloor\frac{y}{100}\right\rfloor + \left\lfloor\frac{y}{400}\right\rfloor - 32045\end{matrix}$$

For a date in the Julian calendar (at noon):

$$\begin{matrix}JDN & = & day + \left\lfloor\frac{153m + 2}{5}\right\rfloor + 365y + \left\lfloor\frac{y}{4}\right\rfloor - 32083\end{matrix}$$

I do not understand how each step works, so can someone please guide me through?

Last edited by a moderator: Jun 22, 2007
2. Jun 15, 2007

D H

Staff Emeritus
It looks like the latter two are formulae for some kind of modified Julian date rather than a Julian date. They also don't like right. Where did you get these? Much better formulae are at the US Naval Observatory web site and Mathworld.

3. Jun 21, 2007

heafnerj

4. Jun 22, 2007

Chronos

5. Jun 24, 2007

thanks guys.