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Jupiter shines brightest in February

Our solar system’s largest planet hits opposition this month, making it a perfect time to watch the dance of its four brightest moons.
RELATED TOPICS: JUPITER
Jupiter on December 30
When viewed through a telescope, Jupiter reveals lots of interesting features.
Damian Peach

Now’s the time to break out the telescope for a long look at Jupiter. The king of planets is making its closest approach to Earth, showing off its subtle features and dancing moons.

Jupiter finder chart
Jupiter lies among the relatively faint background stars of Cancer the Crab at its February peak.
Astronomy: Roen Kelly

Jupiter’s return to opposition happens every 13 months and makes the gaseous giant loom its largest and brightest in our night sky. When it reaches its peak at 1 p.m. EST February 6, the planet will span 45 arcseconds (1 arcsecond equals 1/3,600 of 1°) and shine at magnitude –2.6. That places Jupiter at three times the brightness of the brightest star in the sky, Sirius. It’s easily visible by naked eye, as the only objects in the night sky that are brighter are the Moon and the planet Venus.

Opposition occurs when Jupiter lies directly opposite from the Sun as seen from Earth. That means the planet will rise at sunset and set at sunrise, placing it in the sky all night long. This alignment also puts the solar system’s largest planet highest in the sky at local midnight, where it can be seen through the least amount of Earth’s atmosphere for the best possible view. You’ll easily spot the planet about halfway between the Beehive Cluster (M44), another great binocular target in Cancer the Crab, and 1st-magnitude Regulus, the brightest star in the constellation Leo the Lion.

Jupiter winter 2015 finder chart
The solar system's largest planet will shine brilliantly during the long winter nights. It spends this period near the border between Caner and Leo.
Astronomy: Roen Kelly
At opposition, most will find their telescopes reveal Jupiter’s two dark belts, which are separated by a brighter equatorial zone. And the planet’s increase in apparent size should allow eyepiece views of cloud features in the jovian atmosphere too. Observers also will find it obvious that the planet is not perfectly circular, which is not an illusion. This is caused by the gaseous giant’s composition and rapid rotation. In fact, Jupiter spins completely in under 10 hours, which would allow a dedicated viewer to see the entire planet in just one long winter night.

Jupiter’s four brightest moons, which Galileo discovered in 1610, will also be an excellent sight. These Galilean satellites — Io, Europa, Ganymede, and Callisto (in order of increasing distance from Jupiter) — seldom line up by distance. This happens on the night of opposition. Between sunset and about 2 a.m. EST, an observer can name the moons just by noting how far east of Jupiter they lie.
Jovian moons: Io, Ganymede, and Callisto
Three jovian moons lie near one another the night of February 26/27. Between 9 p.m. and 3 a.m., four mutual events take place among them.
Astronomy: Roen Kelly
One particularly exciting series of events unfolds on the night of February 26. In a six-hour period above North American skies, there will be four interactions between the moons worth staying up for. Starting at 9:17 p.m. EST, Io will pass in front of Ganymede (an occultation). Then at 10:31 p.m., Io’s shadow will envelop Ganymede (an eclipse). At 11:28 p.m., Callisto eclipses Ganymede. And, for the night’s final event, Callisto’s shadow will engulf Io in an eclipse at 2:49 a.m.

The satellites are easy targets in small telescopes and will put on an inspiring period of dozens of these transits, eclipses, and shadows cast on the planet through August 2015.  And for those in cold climes clouded out or not willing to brave the chill, the planet will remain fantastically bright for much of the coming year.
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