For millennia, every December 25, Christians have celebrated the feast of the birth of Jesus Christ. As the Catechism says (525-526):
Jesus was born in a humble stable, into a poor family. Simple shepherds were the first witnesses to this event. In this poverty heaven's glory was made manifest. …
To become a child in relation to God is the condition for entering the kingdom. For this, we must humble ourselves and become little. Even more: to become “children of God” we must be “born from above” or “born of God”. Only when Christ is formed in us will the mystery of Christmas be fulfilled in us. Christmas is the mystery of this “marvelous exchange”...
Now despite what you may have heard, it was the Roman pagans who stole the December 25 celebration from us.
Though it's true that in AD 275, the Roman Emperor Aurelian fabricated December 25 as the pagan “Birth of the Unconquered Sun” celebration at the calendar point when daylight began to lengthen, he didn't randomly chose December 25. If the Emperor had wanted to celebrate the winter solstice, he would have used December 21 as the day of this pagan festival.
That should serve as the first clue.
Paganism was on the outs in the Empire thanks to the concerted efforts of Christians so Aurelian thought like every pagan does―let's get every drunk and they'll be glad to become pagan!
Aurelian was very worried about the seemingly miraculous progress Christianity had made in this Empire and so, in a misguided effort to take the wind out of the Christians' sails, he established Sol Invictus on the very day we had always been celebrating Christ's birth.
In addition, St. Hippolytus of Rome, in his Chronicle written in AD 234, a full 39 years before Aurelian created his pagan festival, clearly explains that Jesus' birth “took place eight days before the calends of January,” that is, December 25.
Oddly, the “December 25 pagan sun festival” idea was originally proffered 300 years ago by Protestant historian Paul Ernst Jablonski. He published his conjecture without offering any proof whatsoever and today, we scramble to explain to people who would rather believe gossip rather than read a history book why they are wrong.
Thus, it's too much of a coincidence to believe Emperor Aurelian randomly chose December 25. Clearly he was trying to pull a scam on pagans and Christians alike.