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.
Tag: Astronomy
Astronomy Items
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
A Brief History of the Universe
Updated August 2026 This post gives a (brief!) history of the Universe from the Big Bang until the the present day. As I am sure you'll agree, it's a big topic; so I'll only give a outline of some of the key events and when we believed they happened. This post is one of many… Continue reading A Brief History of the Universe
Stardust
Last week I was on holiday in London. Â 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. Â Sadly, it can no longer function as… Continue reading Stardust
The Universe Past, Present and Future.
The  Universe is all existing matter and space, including all stars, planets, galaxies and the space between them. This post, which is the first in a series about cosmology discusses the origins of the Universe and its ultimate future. (All my posts on this topic can be found at https://explainingscience.org/tag/cosmology/) How large is the Universe ?… Continue reading The Universe Past, Present and Future.
Explaining Science 