It's great when a Google Doodle celebrates a topic close to our hearts, and the Doodle on 24 October 2024 was a Moon phases game to celebrate the "half Moon" phase.
Following the full Moon on 17 October – the Super Hunter's Moon – on 24 October 2024 the Moon was in its waning phase, losing illumination from the Sun night after night until reaching 'new Moon', which is when it's not illuminated at all.
- See our pick of the best space and astronomy Google Doodles
This is all part of the cycle of the lunar phases caused by the Sun-Earth-Moon system, which determines what section of the Moon is illuminated by sunlight from our perspective on Earth.
The cycle sees more and more of the lunar surface illuminated night after night – known as 'waxing' – taking the Moon from new Moon through crescent Moon, quarter Moon and gibbous Moon to full Moon.
After that cycle, the lit portion of the Moon begins to recede again night after night – known as 'waning' – taking the Moon from full Moon back through gibbous Moon, quarter Moon and crescent Moon to new Moon.
You can see this in cleverly-produced composite images that show the sequence of the Moon phases.
The 24 October Google Doodle celebrated the "Half Moon" cycle, although this isn't, astronomically speaking, entirely correct.
The Moon on 24 October 2024 was the 'third quarter Moon'.
To explain this, let's take 'new Moon' as the beginning of the lunar cycle.
When it's half-lit during the waxing stage of the cycle, it's at 'first quarter'.
Then when the Moon is full, it's halfway through the cycle of lunar phases.
And after full Moon, when it's half-lit during the waning stage of the cycle, it's 'third quarter'.
The Moon does appear to be half-lit and half-unlit, which is why these phases are known informally as a 'half Moon', but astronomers and Moongazers refer to these stages as 'quarter Moons'.
How to play the Half Moon Google Doodle
The Google Doodle game plays out a bit like a game of tic-tac-toe, where you play against the 'computer' to match different cards showing different phases of the Moon.
One way of creating a match and earning a point is to pick a card that's identical to the one already played, e.g. placing a waxing crescent to match a waxing crescent. This is a 'phase pair'.
Another way is to pick a card that matches the opposite phase to the one already played, e.g. a waxing crescent to match a waning gibbous. This is a 'full Moon pair'.
And the third way is to insert a card that fills in a missing piece of the lunar phase sequence, e.g a waxing crescent between a new Moon and a first quarter Moon. This is a 'lunar cycle'.
Win three levels against the 'computer' and you've won the game! The first level is played on a 3x3 board, then level two on a 4x3, and the levels get increasingly bigger thereafter.
You can play by going to the Rise of the Half Moon Google Doodle page.
