Look low in the southwest sky at dusk and nightfall on December 18, 2013 to behold the sky’s brightest planet, Venus. After you first see this dazzling world, it’ll quickly sink downward, to follow the sun beneath the horizon an hour or so after sunset. Before Venus disappears, though, as this very bright planet hovers over your western horizon, turn around to view the moon and the planet Jupiter rising in tandem over the east-northeast horizon.
If your horizon isn’t level, you may have to wait till after Venus sets before you can view the moon and Jupiter’s picturesque ascent into the starry sky. Once the waning gibbous moon and the king planet Jupiter make their appearance at early evening, however, they’ll be out together for the rest of the night.
The moon and Jupiter will move across the sky tonight from east to west for the same reason that the sun moves from east to west during the day. The Earth rotates on its axis from west to east, making it appear as if the sun, moon, planets and stars travel from east to west across the sky while the Earth is at rest. Educated people now know it’s the Earth that does the moving, spinning full circle relative to the sun in about 24 hours.
When Galileo discovered the four major moons of Jupiter in the early 1600’s, he saw that Jupiter’s moons revolve around Jupiter. This suggested the possibility of Earth revolving around the sun. We now know the Earth revolves around the sun in approximately 365 and ¼ days.
With only a modest telescope – or possibly binoculars – you can view Jupiter’s four major moons for yourself. Click here to know their positions of these moons as seen from Earth. Going outward from Jupiter, these moons are Io, Europa, Ganymede and Callisto.
Bottom line: Tonight – December 18, 2013 – you’ll see Venus in the sunset direction shortly after the sun goes down. Then turn opposite Venus in the sky to find the nearest bright light to the moon. That’ll be Jupiter, the fourth-brightest celestial body to light up the heavens, after the sun, moon and Venus.