The Orthodox church of Russia is still using the old Julian calendar, which means that December 25th for us is January 7th for them. For that reason even in late January you see lots of Christmas trees, Christmas markets and light installations all over Moscow.
A Christmas tree at Tretyakovskaya Art Gallery
Light installations at Sokolniki Park
Kitschy animals at Sokolniki Park
Summer will come
The cold is not that bad if you wear the right clothes.
The Christmas Market on the Red Square
So when you're in Moscow in January, be prepared for Christmas!