Mercury and Antares about 45 minutes before sunrise tomorrow morning low in the southeastern sky. Maps created with Stellarium

Early morning risers can see the planet Mercury shining on the level with Antares, the brightest star in Scorpius the Scorpion tomorrow morning low in the southeastern sky at dawn. Depending on exactly when you go out to look, the sky will be lit with twilight, so bring binoculars just in case. The map above is drawn for around 7:15 a.m. local time. Mercury, located in the constellation Ophiuchus, will shine about a half magnitude brighter than Antares, a red supergiant star. Can you see the color difference between the two? Through a telescope, the planet looks like a very tiny version of the waxing gibbous moon.

First Europa and then Io reappear at the times shown after being eclipsed by Jupiter's shadow. Each takes several minutes to fully emerge into sunlight. The black dots are the moons in shadow; the white as seen in sunlight. Shadow outline is approximate.

Tonight Dec. 29 Jupiter’s moons are once again at center stage. Anyone with any kind of telescope will be able to watch the amazing sight of two moons materializing from empty space as they leave the planet’s shadow and reappear in sunlight. Europa and Io are hidden in Jupiter’s shadow before 6:45 p.m. Central time, but a minute or two later, Europa slowly reappears a little more than one Jupiter-diameter to the east of the planet. Faint at first, it will soon brighten as the entire moon gradually exits the dark shadow. If we could see it up close, we’d watch the shadow slips across Europa’s disk much like the Earth’s shadow during a total lunar eclipse.

The same happens to the moon Io about 40 minutes later a bit closer to the planet. Be sure to start watching both these “eclipse reappearances” 5-10 minutes BEFORE the times shown, so you can watch and appreciate the full transition from invisibility to return to normal brightness. By the time they’re finished, Jupiter will have two “new” moons compared to the hour before. I hope you get to see it. Oh, just to be sure you know where to find Jupiter in the first place, it’s that very bright “star” high in south at nightfall.