The celebration of Christmas varies, with most Christians observing it on December 25, while Orthodox Christians celebrate on January 7 due to differences from the Julian to Gregorian calendars. These calendar changes, initiated by Pope Gregory XIII in 1582, addressed drift issues in previous systems, affecting seasonal alignment and date consistency in Christian practices.
Author: Steve Hurley
Hi I am Steve Hurley. Although I work in the IT industry. I studied for a PhD in astronomy in the 1980s. My real passion is explaining scientific concepts to a non-scientific audience. My blog (explainingscience.org) covers various scientific topics, but primarily astronomy. It is written in a style that it is easily understandable to the non scientist.
Publications and videos
For links to my books and videos please visit www.explainingscience.org
The Shortest Day
Updated and revised 11 December 2025 As I write this post, it's completely dark outside and it's only 5 o'clock in the afternoon. Today is 4 December, and most people I come across think that it will continue to get dark earlier and earlier in the afternoons until 21 December, the shortest day of the year… Continue reading The Shortest Day
The Universe’s History: From Big Bang to Today
Updated 20 November 2025 his post covers a brief history of the Universe from the Big Bang until the the present day. This, as I am sure you'll agree, is a pretty big topic so I'll only give a outline of some of the key events and when we believed they happened. This post is… Continue reading The Universe’s History: From Big Bang to Today
Philae has landed
Like millions over people I was cheered to see that the probe Philae landed successfully on the 67P/Churyumov-Gerasimenko comet after a 6.4 billion km ten year journey. In a mission this complex there will inevitably be a few hiccups and the biggest one so far has been that the probe has been unable to secure itself to… Continue reading Philae has landed
Stardust
Last week I was on holiday in London. While I was there, I spent an afternoon at the Royal Greenwich Observatory, which is set on top of a hill in East London. It was commissioned in 1675, making it one of the oldest astronomical observatories in the world. Sadly, it can no longer function as… Continue reading Stardust
Explaining Science 