“This is close enough to midnight that the Full Moon will be on the next day in Coordinated Universal Time (UTC), so many calendars will show the Full Moon on December 30, 2020.
“The Moon will appear full for about three days around this time, from Monday evening through Thursday morning.”
In astronomical terms, a Full Moon only lasts for a brief moment, when the Moon finds itself 180 degrees from the Sun.
When viewed from London in the UK, this will happen at about 3.28am GMT on Wednesday.
After that, the Moon will set in the northwest at about 8.36am GMT and rise again in the northeast by about 4.10pm GMT.