Robin's Blog

Free Julian Day calendar poster download

I often find myself using Julian days as a simple method to represent dates in my code. It’s nice and easy, because every day is simply an integer (the number of days since the beginning of the year) and any time during the day can be represented as a floating point number (the fraction of that day which has elapsed at that point).√ā¬†Furthermore, lots of satellite imagery is provided with the dates specified as Julian days – for example, MODIS data filenames include the year and then the Julian day.

It’s fairly easy to convert a standard date (eg. 24th March) to the Julian day in most programming languages (there will either be a library function to do it, or it’s fairly simple to write one yourself) – but it’s not that easy to do in your head. So, I have created a Julian Day calendar poster:

Julian Day Calendar ThumbnailIt’s a very simple table that lets you choose the month and day, and get the Julian Day number. Just make sure you remember the note at the top – add one to the number (after February) if it’s a leap year!

It’s available for download below:

Julian Day Calendar – PNG

Julian Day Calendar – PDF

Categorised as: Academic, GIS, Remote Sensing


  1. Diana Day says:

    Very cool!! Just googling my son’s name! Thank you for this :):)

  2. […] Free Julian Day calendar poster download […]

  3. Doug Brooks says:

    Excellent!! A must have for every real estate agent!!

  4. Dave the nerd says:

    These are not Julian days – google it. These are days of the year (DOY). Common misconception, but incorrect.

  5. Robin Wilson says:

    Yes, you’re right. Unfortunately in my field (satellite imaging) 99% of people (including organisations that should know better) refer to them as Julian Days, so that’s what I’ve done. I will add a clarification note to the entry.

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