Our planet Earth flies between the sun and the outer planet Jupiter on May 8 (if you’re in the Americas or Pacific) or May 9 (for time zones in the rest of the world). That passage places Jupiter – largest world in our solar system, and a very bright planet in our sky – opposite the sun. In other words, Jupiter is now rising in the east as the sun is setting below the western horizon. Astronomers call this event an opposition of Jupiter.
Opposition marks the middle of the best time of year to see a planet. That’s because it’s when the planet is up all night and generally closest for the year (the exact date of Jupiter at its closest this year is May 10).
Your astronomical calendar for 2018 likely gives the date and time of Jupiter’s 2018 opposition as May 9 at 1 UTC. That translates to May 8 at 8 p.m. Central Daylight Time in North America (translate UTC to your time).
Rising in the east around sunset, Jupiter climbs highest in the sky at midnight. It sets in the west around sunrise. Jupiter is always bright; it’s the largest planet in our solar system. It shines more brightly than any star in the evening sky.
With the exception of the sun and moon, only Venus – the brightest planet, now in the west after sunset – outshines Jupiter. Try catching both Venus and Jupiter at nightfall now. Venus will be blazing low in the west and Jupiter, a bit fainter but still brighter than any star, will be shining in the east. Venus will set as Jupiter ascends in the eastern sky.
At this 2018 opposition, Jupiter shines in front of the constellation Libra the Scales. The closest 2nd-magnitude star to Jupiter is Zubenelgenubi, Libra’s alpha star. Dazzling Jupiter – a planet in our own solar system and much closer to us than any star – outshines Zubenelgenubi by over 100 times.
Jupiter comes to opposition about every 13 months. That’s how long Earth takes to travel once around the sun relative to Jupiter. As a result – according to our earthly calendars – Jupiter’s opposition comes about a month later each year.
Last year – in 2017 – Jupiter’s opposition date was April 7.
Next year – in 2019 – it’ll be June 10.
Astronomer Guy Ottewell has a great post at his blog this week on Jupiter’s opposition and its location in our sky this year. The charts below (used with permission) are from Guy:
There’s a NASA spacecraft orbiting Jupiter now. The Juno spacecraft’s orbit carries it low over Jupiter’s poles, providing never-before-seen glimpses of the giant planet’s polar regions. Jupiter isn’t a rocky planet like Earth. It’s more like a failed star, not massive enough or hot enough inside to spark thermonuclear fusion reactions, but some 2.5 times more massive than all the other planets in our solar system combined. Jupiter shows us nature magnified! Check out the video below, which provides an infrared view of the massive cyclones at Jupiter’s poles:
— NASA's Juno Mission (@NASAJuno) April 11, 2018
Bottom line: Look for Jupiter on the night of May 8-9, 2018, as this world comes to opposition, the point opposite the sun in our sky. You’d need some 80 Jupiters – rolled into a ball – to be hot enough inside for thermonuclear reactions … for Jupiter to shine as stars do. Yet on this May night – as Jupiter rises opposite the sun – you can imagine it beaming down on us as a tiny sun all night long.