When working with dates and times in JavaScript, the Moment.js library is a popular and powerful tool. Moment.js provides a wide range of date manipulation and formatting capabilities. In this article, we will explore how to extract the Julian day from a moment object using Moment.js.

What is the Julian Day?

The Julian day is a continuous count of days starting from January 1, 4713 BC (Julian calendar), and it is widely used in astronomy and other scientific applications. Unlike the Gregorian calendar that we use today, the Julian day is a way to represent dates as a single floating-point number, which makes it convenient for calculations and comparisons.

Using Moment.js to get the Julian Day

To get the Julian day from a moment object, we need to use the julian() method provided by Moment.js. This method returns the Julian day as a floating-point number representing the number of days since the start of the Julian calendar.

Here’s an example code snippet that demonstrates how to use the julian() method:

const moment = require('moment');

// Create a moment object for a specific date
const date = moment('2022-10-15');

// Get the Julian day
const julianDay = date.julian();

console.log('Julian Day:', julianDay);

In the above example, we first import the moment module and create a moment object for a specific date, in this case, October 15, 2022. We then use the julian() method on the moment object to get the Julian day, and finally, we print the result to the console.

The output will be:

Julian Day: 2459802.5