# 2.15.2. What is the modified Julian day number?

## Description

This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by
others.

# 2.15.2. What is the modified Julian day number?

Sometimes a modified Julian day number (MJD) is used which is

2,400,000.5 less than the Julian day number. This brings the numbers

into a more manageable numeric range and makes the day numbers change

at midnight UTC rather than noon.

MJD 0 thus started on 17 Nov 1858 (Gregorian) at 00:00:00 UTC.

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