Look for the moon as soon as darkness falls on Sunday, March 9, 2014. Jupiter is still the brightest planet nearby and will continue to be for several more nights. On Sunday night, the moon and Jupiter are separated by about 7 degrees on the sky’s dome, as seen from North America (a closed fist at arm’s length covers 10 degrees of sky). These two beautiful luminaries will be out until late Sunday night, when both will set in the west.
The giant planet Jupiter has more than twice the mass of all the other solar system planets, dwarf planets, asteroids and moons combined. Jupiter’s mass is 318 times that of the Earth. Little wonder why Jupiter enjoys the King Planet designation!
Three of Jupiter’s four largest moons are larger and more massive than Earth’s moon. In their outward order from Jupiter, they are Io, Europa, Ganymede and Callisto. Only Europa is a touch smaller and less massive than our own moon.
In fact, you can view these moons as pinpoints of light with a modest backyard telescope or even good binoculars. See the present position of Jupiter’s moons on this handy chart, courtesy of skyandtelescope.com.
We’ve been asked why Jupiter’s moons move so quickly around Jupiter, although all four of Jupiter’s major moons lie farther away from Jupiter than our moon’s distance from Earth. For instance, Io – Jupiter’s closest moon – has a semi-major axis of 421,800 kilometers in contrast to the semi-major axis of our moon of 384,400 kilometers. Despite Io’s greater distance from its parent planet, Io revolves around Jupiter in 1.769 days. Meanwhile, our moon takes a whopping 27.322 days to orbit Earth.
It’s Jupiter’s great mass that causes Io and Jupiter’s moons to move so quickly around Jupiter. If the Earth were as massive as Jupiter, then our moon’s orbital period would be only 1.53 days. Or if Jupiter were as lightweight as Earth, then Io’s orbital period would be 31.55 days.
Bottom line: Use the waxing gibbous moon to find Jupiter, the king of the planets, on Sunday, March 9!