Ruby – Get the Julian Day Number – jd() Method – Examples & Explanation

jd() method exists in Standard Date Library of Ruby. The purpose of this method is to generate a date object indicating the given chronological Julian day number.

In date, the syntax of jd() method is:

Date.jd(x)

x is any valid Julian date object. This parameter is required.
Note: If the x parameter is not a valid Julian date object jd() method will return an error and if it is zero, it will show the start of the calendar like -4712-01-01.

jd() method generates a new date object by indicating from a string given in a code.

The date format for Julian (JUL) is CYYDDD.
Here YY represents the year and the DDD indicates the day of the year.

# import date library
require 'date'
x = Date.jd(2457000)
puts x

Output
2014-12-08

# import date library
require 'date'
x = Date.jd(0)
puts x 

Output
-4712-01-01

Note: In the above code (0) represents the start of the Julian Calendar Date as given in the output.

To covert the Julian date to current Calendar Date see the following example.

# import date library
require 'date'
julian = "14125"
puts Date.strptime(julian, "%y%j")

Output
2014-05-05

NOTE: In the above code (14125), 14 represent the year and 125 is represents the day of the year.

# import date library
require 'date'
current_date = DateTime.now.amjd().to_f   	# Date: 2016-15-07
puts current_date

Output
57959.19037960804

NOTE: The amjd() function is used to convert the current date into Julian date and then converting the output into float is helpful to understand easy.