At 17:11 UTC, the very time of this posting, the December solstice occurred.
The word solstice comes from mid-13c., from Old French solstice (13c.), from Latin solstitium “point at which the sun seems to stand still,” especially the summer solstice, from sol “sun” (see sol) + past participle stem of sistere “to come to a stop, make stand still” (see assist (v.)).
One mis-conception about the December solstice (same for the June Solstice) is it occurs on the same day. While most of the time the winter solstice does fall on 21 December, depending on the moon the date can change a little.
The moon? Yep, the moon.
Watch the ISS spacewalks at the NASA TV link just below the banner at the top of the page.by