In 2012, Jupiter – largest planet in our solar system – will come nearest to Earth on December 1, at 15 hours UT (9 a.m. Central Standard Time). Then Jupiter will be only 378 million miles (609 million kilometers) away from us – still very, very distant – but closer than it will be again until the year 2021.
Why is Jupiter especially close in early December 2012? Jupiter comes closest to Earth once each year, when our planet flies between Jupiter and the sun. Earth will fly between the sun and Jupiter next on December 3 at 2 UT. That is 8 p.m. Central Standard Time on December 2. We’ll go between the sun and Jupiter in early December, and that movement of Earth will place Jupiter opposite the sun in our sky – in other words, rising in the east as the sun is setting in the west.
When it is opposite the sun, astronomers say that Jupiter is in opposition to the sun. Jupiter comes to opposition once every 13 months or so, because Earth takes a year to orbit the sun, in contrast to Jupiter’s 12-year orbit. Our orbit is closer to the sun than Jupiter’s. Plus we move faster in orbit than Jupiter does. Earth travels at a speed of about 18 miles per second in orbit, in contrast to about 8 miles per second for Jupiter.
Why are some oppositions of Jupiter closer than others? It’s because Jupiter’s orbit, like Earth’s orbit, isn’t round. It’s very nearly round, but not perfectly so. Jupiter passed its perihelion – or closest point to the sun – in March 2011. Since then, the giant planet has been getting farther from the sun in its 12-year orbit, and it will continue to get farther from the sun each year until its aphelion – or farthest point from the sun – in 2017.
In 2011, when Jupiter swung in closest to the sun at perihelion, it was nearly 50 million miles closer to the sun than it will be at aphelion – its most distant point. We’re swinging between the sun and Jupiter in early December. Jupiter is farther from the sun than it was at opposition last year, but it’s closer to the sun than it will be a year from now. Thus when we fly between the sun and Jupiter on December 2-3, 2012, Jupiter will be closer to us than it will be next year … or in the years following.
In the coming years, Jupiter will be moving farther from the sun in its orbit, and so it’ll be progressively farther from Earth at each year’s opposition.
When will Jupiter be farthest from Earth in the coming year? Jupiter’s greatest distance from us in the coming 12 months will come when Jupiter passes directly behind the sun from Earth in June 19, 2013. Let’s see … closest in early December 2012 … farthest a bit more than six months later in June 2013. You might see that Jupiter’s distance from us, as well as its location in our sky, is being driven primarily by Earth’s year-long orbit around the sun.
Bottom line: Jupiter will be closer to Earth on December 1, 2012 than it will be again until the year 2021. It is closest around the time of its yearly opposition, which comes on December 2-3, 2012. Jupiter will remain close and bright throughout December and January 2013. Although it’ll dim slightly throughout December and January, more people will notice Jupiter in these months than in December, because Jupiter will appear in the east already as the sun is setting in the west.