Mercury is usually a shy and elusive catch for naked-eye skywatchers, but for the next few days it shows itself boldly if you look at the right time.
Mercury is the closest planet to the Sun — so from our point of view, it spends nearly all its time either hidden by the Sun's blinding glare or out of sight below the horizon when the Sun is gone too. But from now through the weekend, you can spot Mercury glittering at its best above the southwest horizon in twilight.
The best time to look will be from about 30 to 60 minutes after your local sunset time. Earlier than that the sky will still be very bright, and later than that Mercury will be sinking very low. But during that window, you should have no trouble if your southwestern sky is clear.
There's a legend that Copernicus himself never saw Mercury. It's almost certainly false, even given his high latitude and foggy weather (on the north coast of what is now Poland) that would have made Mercury more difficult than for most of us. But the story does highlight Mercury's elusiveness. It's in this good an evening view for just two or three weeks a year, and even then for less than an hour out of every 24.
You'll need to find an open view to the southwest. If Mercury is hidden behind buildings or trees, spot Altair higher in the west-southwest. Hold your fist out at arm's length. The area of sky you want to see is lower left of Altair by about three fists at arm's length (30°).
After Sunday January 3rd, Mercury will remain almost as high in twilight for another week, but it will fade very rapidly. It shines at magnitude –0.5 to 0.0 from December 30th through January 3rd, but dims to a mere 2nd magnitude by January 8th.
Mercury is the only bright planet these evenings, but bigger things await later at night. By midnight, Jupiter is up and blazing low in the east. And after the midnight celebrations on New Year's Eve, you'll find the Moon shining eerily below it.
Note: The sky descriptions are for the world's mid-northern latitudes: the U.S. (except Alaska) and southern Canada, southern Europe, Central Asia, China, and Japan.