ELI5 Winter Solstice - why it marks the start of winter, not the middle of it?

If the winter solstice is the longest night of the year, why does it mark the beginning of winter? Shouldn’t it rather mark the very middle of it? Why not have new years day be on the winter solstice?  ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: 2biggij, bobbyp27, zmech, markusx06, enigmasolver and mallad To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]